ASE 1 - Engine Repair
ASE 1 - Engine Repair
Module 7
General Engine Diagnosis
Acknowledgements
General Motors, the IAGMASEP Association Board of Directors, and Raytheon Professional
Services, GM's training partner for GM's Service Technical College wish to thank all of the
people who contributed to the GM ASEP/BSEP curriculum development project 2002-3. This
project would not have been possible without the tireless efforts of many people. We
acknowledge:
•
The IAGMASEP Association members for agreeing to tackle this large project to create
the curriculum for the GM ASEP/BSEP schools.
•
The IAGMASEP Curriculum team for leading the members to a single vision and
implementation.
•
Direct contributors within Raytheon Professional Services for their support of translating
a good idea into reality. Specifically, we thank:
– Chris Mason and Vince Williams, for their leadership, guidance, and support.
– Media and Graphics department under Mary McClain and in particular, Cheryl
Squicciarini, Diana Pajewski, Lesley McCowey, Jeremy Pawelek, & Nancy
DeSantis.
– For his help on the Engine Repair curriculum volume, Subject Matter Expert,
Stephen Scrivner, for his wealth of knowledge.
Finally, we wish to recognize the individual instructors and staffs of the GM ASEP/BSEP
Colleges for their contribution for reformatting existing General Motors training material, adding
critical technical content and the sharing of their expertise in the GM product. Separate
committees worked on each of the eight curriculum areas. For the work on this volume, we
thank the members of the Engine Repair committee:
– Rick Frazier, Owens Community College
– Victor Ginoba, Northern Virginia Community College
– Marty Kamimoto, Fresno City College
– Tony Kossman, Hudson Valley Community College
– Mike Parker, New Hampshire Community Technical College
– Rory Perrodin, Longview Community College
Contents
Module 7 – General Engine Diagnosis
Acknowledgements .......................................................................................... 2
Introduction ...................................................................................................... 5
Objectives ........................................................................................................ 5
Lesson 1: Oil/Fluid Leak Diagnosis ................................................................................. 8
Introduction ..................................................................................................................... 8
Objective ......................................................................................................................... 8
Fluid Leaks ..................................................................................................................... 8
Lesson 2: Engine Mechanical Noises ........................................................................... 14
Introduction ................................................................................................................... 14
Objective ....................................................................................................................... 14
Primary Abnormal Engine Noises ................................................................................. 14
Lower Engine Noise ...................................................................................................... 16
Internal Components..................................................................................................... 20
Inspections for the Various Components ...................................................................... 22
Lower Engine Noise ...................................................................................................... 30
Internal Causes of Lower Engine Knock ....................................................................... 33
Lesson 3: Base Engine Misfire Test .............................................................................. 37
Introduction ................................................................................................................... 37
Objective ....................................................................................................................... 37
Base Engine Misfire Procedure .................................................................................... 37
OBD System Check ...................................................................................................... 39
DTC P0300 Engine Misfire Diagnosis Chart ................................................................. 41
Misfire Counter Check (Single) ..................................................................................... 43
Test Lamp J 26792 / ST 125 Spark Testing .................................................................. 44
Injector Coil Test ........................................................................................................... 44
Base Engine Misfire Table ............................................................................................ 45
Lesson 4: Static Compression Test ............................................................................... 46
Introduction ................................................................................................................... 46
Objective ....................................................................................................................... 46
Static Compression Test ............................................................................................... 46
Lesson 5: Running Compression Test .......................................................................... 48
Introduction ................................................................................................................... 48
Objective ....................................................................................................................... 48
How to Perform a Running Compression Test .............................................................. 48
Lesson 6: Cylinder Leakage Test .................................................................................. 50
Introduction ................................................................................................................... 50
Objective ....................................................................................................................... 50
Cylinder Leakage Test - Testing Procedure .................................................................. 50
Lesson 7: Restricted Exhaust Test ................................................................................ 53
Introduction ................................................................................................................... 53
Objective ....................................................................................................................... 53
Restricted Exhaust Diagnostic Chart ............................................................................ 53
Lesson 8: Vacuum Test ................................................................................................. 55
Introduction ................................................................................................................... 55
Objective ....................................................................................................................... 55
Vacuum Test Diagnosis Chart ....................................................................................... 57
Lesson 9: Oil Pressure Test .......................................................................................... 58
Introduction ................................................................................................................... 58
Objective ....................................................................................................................... 58
Engine Oil Functions ..................................................................................................... 58
Lesson 10: Engine Speed-Related Vibrations .............................................................. 62
Introduction ................................................................................................................... 62
Objective ....................................................................................................................... 62
Isolating Vibrations ........................................................................................................ 62
Exercise 7-1 .................................................................................................................. 66
Introduction
Student Workbook
After completing this unit, the technician will demonstrate an
understanding of general engine diagnosis. The technician will also
demonstrate the skills required to troubleshoot general engine
diagnosis and general engine customer concerns.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objectives
NATEF Area A1
A. General Engine Diagnosis; Removal and Reinstallation (R & R)
1. Identify and interpret engine concern; determine necessary
action.
2. Research applicable vehicle and service information, such as
internal engine operation, vehicle service history, service
precautions, and technical service bulletins.
3. Locate and interpret vehicle and major component identification
numbers (VIN, vehicle certification labels, and calibration
decals).
4. Inspect engine assembly for fuel, oil, coolant, and other leaks;
determine necessary action.
5. Diagnose engine noises and vibrations; determine necessary
action.
6. Diagnose the cause of excessive oil consumption, unusual
engine exhaust color, odor, and sound; determine necessary
action.
7. Perform engine vacuum tests; determine necessary action.
8. Perform cylinder power balance tests; determine necessary
action.
9. Perform cylinder compression tests; determine necessary
action.
10. Perform cylinder leakage tests; determine necessary action.
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7-5
Engine Repair
Student Workbook
D. Lubrication and Cooling Systems Diagnosis and Repair
1. Perform oil pressure tests; determine necessary action.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
STC Tasks:
A. Engine Mechanical Diagnosis and Testing
1. Describe the process for conducting a compression test
2. Describe the process for conducting an engine vacuum test
3. Describe the cylinder leakage test
4. Describe the fluid leak diagnosis process
5. Describe the oil pressure test procedure
6. Describe camshaft timing and related diagnostics
8. Describe engine mechanical diagnostic procedures
9. Verify driver's complaint, perform visual inspection and/or road test
vehicle; determine needed action
10.Research applicable vehicle information, such as engine
management system operation, vehicle service history, service
precautions, and technical service bulletins.
11. Diagnose the cause of unusual engine noise and/or vibration
problems; determine needed action
12. Diagnose the cause of unusual exhaust color, odor, and sound
13. Perform engine manifold vacuum or pressure tests
14. Perform cylinder power balance test
15. Perform cylinder cranking compression test
16. Perform cylinder leakage test
18. Verify correct camshaft timing
19. Verify proper engine operating temperature, check coolant level
and condition
22. Diagnose the cause of excessive oil consumption
23. Diagnose the cause of excessive coolant consumption
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2002 General Motors Corporation
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7-6
I. Verify customer concerns, make quick checks and perform a system
diagnostic check related to engine mechanical system faults.
1. Describe how to perform a system diagnostic check.
J. Perform engine valve timing component service procedures.
1. Remove and install the engine valve timing components.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
L. Perform engine diagnostic procedures.
1. Perform engine vacuum gauge diagnostic check.
2. Perform an engine external oil leak diagnostic check.
O. Perform an engine compression test.
1. Perform an engine compression test.
R. Perform an engine cylinder leakage test.
1. Perform an engine cylinder leakage test.
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2002 General Motors Corporation
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7-7
Lesson 1: Oil/Fluid Leak Diagnosis
Introduction
After completing this unit, the technician will demonstrate an
understanding of oil leak diagnosis. The technician will also demonstrate
the skills required to troubleshoot oil leak diagnosis and address customer
concerns.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
Describe the procedures to check for oil leaks and identify possible
sources of oil leaks.
Notice:
It is important to correctly identify the source of an oil leak. A power
steering fluid leak or spillage can travel across the valley area of the
engine and run out the weep hole, which is located at the back of the
block. Failure to correctly identify the source of an oil leak can lead to the
incorrect or unnecessary replacement of components.
Fluid Leaks
Although oil is one of the main fluids in the engine compartment, there are
several other types of fluid that can be mistaken for an oil leak. Many
times as fluid migrates through the engine compartment, it will pick up
debris and may not be easy to identify.
Engine Compartment Fluids
•
Coolant
•
Power steering fluid
•
A/C PAG oil
•
Transmission fluid
•
Front axle lube
•
Electrolyte
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2002 General Motors Corporation
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7-8
Any of these fluids can migrate from the leak point and travel down the
engine. You can repair most fluid leaks by first visually locating the leak,
repairing or replacing the component, or by resealing the gasket surface.
Once the leak is identified, determine the cause of the leak. Repair the
cause of the leak as well as the leak itself.
Student Workbook
To determine if the leaking fluid is engine oil, transmission fluid, power
steering fluid, brake fluid, or some other fluid, use the visual inspection
method.
Module 7 - General
Engine Diagnosis
ASE 1 - Engine
Repair
Visual Inspection Method
1. Bring the vehicle to normal operating temperature.
2. Park the vehicle over a large sheet of paper, or other clean surface.
3. Wait several minutes, and then check for drippings.
4. Identify the type of fluid, and the approximate location of the leak.
5. Visually inspect the suspected area. Use a small mirror to assist in
looking at hard to see areas.
6. Check for leaks at sealing surfaces, fittings, or from cracked or
damaged components.
7. If you cannot locate the leak, do the following:
a. Completely clean the entire engine and surrounding components.
b. Operate the vehicle for several miles at normal operation
temperature and at varying speeds.
c. Park the vehicle over a large sheet of paper, or other clean surface.
d. Wait several minutes, and then check for drippings.
e. Identify the type of fluid, and the approximate location of the leak.
f. Visually inspect the suspected area. Use a small mirror to assist in
looking at hard to see areas.
g. See possible causes for leaks.
If you still cannot locate the leak, use the powder method or the black light
and dye method.
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7-9
Powder Method
Student Workbook
1. Completely clean the entire engine and surrounding components.
2. Apply an aerosol-type powder (baby powder, foot powder, etc.) to the
suspected area.
ASE 1 - Engine
Repair
3. Operate the vehicle for several miles at normal operation temperature
and at varying speeds.
Module 7 - General
Engine Diagnosis
4. Identify the type of fluid, and the approximate location of the leak, from
the discolorations in the powder surface.
5. Visually inspect the suspected area. Use a small mirror to assist in
looking at hard to see areas.
6. See possible causes for leaks.
To identify the source of the leak, it's often necessary to use leak dye to
identify the leak point and thus the type of fluid.
Black Light and Dye Method
1. A dye and light kit is available for finding leaks. Use the J 28428-E
or equivalent. Refer to the manufacturer's instructions when using
the tool.
2. Visually inspect the suspected area. Use a small mirror to assist in
looking at hard to see areas.
3. See possible causes for leaks.
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7-10
Leak Checking Procedure
•
•
The leak dye and black light is one of the best methods for isolating
leaks.
Prior to dye installation, check for presence of dye in engine
compartment using black light.
•
Dyes for many of the fluids in an engine compartment are all the same
color. If they were previously used, there may still be traces, so clean
them off to prevent misdiagnosis.
•
Next, pour the dye into crankcase and start engine to allow dye to
circulate through engine oil passages.
•
The engine should run for several minutes to allow the dye to migrate
to the leak point.
•
Then use black light to search for dye. Use goggles since they
enhance the dye.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-1, Leak Checking
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2002 General Motors Corporation
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7-11
Notice:
Student Workbook
Remember, small leaks may require additional time to become visible.
Leak may only occur as the engine cools down.
Important:
Do not get dye on the vehicle finish since it can damage the paint.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Possible Causes for Leaks
Check for the following conditions:
•
Higher than recommended fluid levels
•
Higher than recommended fluid pressures
•
Plugged or malfunctioning fluid filters or pressure bypass valves
•
Plugged or malfunctioning engine ventilation system
•
Improperly tightened or damaged fasteners
•
Cracked or porous components
•
Improper sealants or gaskets where required
•
Improper sealant or gasket installation
•
Damaged or worn gaskets or seals
•
Damaged or worn sealing surfaces
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7-12
Loss of Coolant
Student Workbook
1. Check for an incorrect or faulty surge tank cap.
2. Ensure that the cooling system is full.
3. Pressure test the cooling system.
4. While the cooling system is pressurized, inspect for any external
coolant leaks.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
5. Repair or replace the leaking component(s) as necessary.
6. Check the heater core for leakage
7. Start the engine and inspect.
8. Check for excessive white smoke from the exhaust and/or rough
engine idle.
9. Road test the vehicle and allow the engine to reach full operating
temperature.
10. Make sure the engine does not overheat.
11. Remove the oil level indicator stick and inspect.
Important:
Ensure that the cause of the creamy or milky substance is not caused by
short drive cycles or a faulty thermostat. Either of these conditions will
cause creamy or milky deposits to form in the engine oil because the
engine cannot reach full operating temperature in order to dissipate the
condensation/moisture.
12. Make sure the engine reached full operating temperature during all of
the vehicle drive cycles. The probable cause of the coolant loss is an
engine internal coolant leak. If the spark plug electrodes or the
porcelain surrounding the spark plug electrodes exhibit signs of
coolant, replace the applicable cylinder head(s) or cylinder head
gasket(s).
13. Ensure that the cooling system is full. (Refer to Draining and Filling
Cooling System).
14. Operate the system in order to verify the repair.
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2002 General Motors Corporation
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7-13
Lesson 2: Engine Mechanical Noises
Introduction
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine mechanical concerns.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
•
Identify the primary types of engine mechanical noise.
•
Explain what engine noises sound like.
•
Explain how engine noise can be affected by load.
•
Identify the type of engine faults that can cause the various engine
noises.
•
Explain how engine noise can cause a misfire DTC.
There are four steps to diagnosing engine noise. You must determine the
following conditions:
•
Type of noise.
•
Determine the exact operating condition under which the noise exists.
•
At what rate, and at what location in the engine.
•
Compare sounds in other engines to make sure you are not trying to
correct a normal condition.
Primary Abnormal Engine Noises
There are two broad categories that the service information uses to
classify noise.
•
Upper engine or valve train noise: generally associated with tick.
•
Lower engine noise: generally associated with knock
In order to make the best use of the service information you must be able
to classify an engine noise in one of these two categories.
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2002 General Motors Corporation
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7-14
Upper Engine (Valve Train) Noise
Student Workbook
Valve train noise is generally associated with a ticking noise. Although not
all valve train noises make the same type of ticking noise, their occurrence
will be related to the speed of the camshaft.
ASE 1 - Engine
Repair
Valve train noise is related to engine speed:
•
The camshaft drives valve train components.
•
The camshaft rotates at half the speed of the crankshaft; therefore,
valve train noises will be at 1/2 engine speed.
•
Engine speed is based on the crankshaft speed.
•
For example, if the engine speed is 600 RPM, the cam speed will be
300 RPM. The valve train noise will occur 5 times per second.
Module 7 - General
Engine Diagnosis
General Sources of Valve Train Noise
•
Camshaft(s)
•
Lifters/Stationary Hydraulic Lash Adjusters (SHLA)
•
Pushrods
•
Rocker arms
•
Valve components
•
Guides
•
Carbon build up on valves
•
Timing chain
•
Balance shaft
Noises related to these items will increase in frequency as the engine
RPM increases. For example, as the engine RPM increases they will
occur more often, but still at half engine RPM.
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2002 General Motors Corporation
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7-15
Lower Engine Noise
General Sources
Lower engine noise is generally associated with a knocking noise, and
occurs once per engine revolution. At 600 RPM, a lower engine noise will
occur 10 times per second.
Lower Engine Knocking Sources
•
Piston slap
•
Main/rod bearing knock
•
Piston pin knock
•
Flywheel (loose or broken)
•
Carbon in the combustion chamber
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Noises related to these items will increase in frequency as the engine
RPM increases, and are directly related to engine RPM. However, some
knock noises will be more pronounced when the cylinder is under
pressure during the compression and power strokes. Engine noises can
change with engine load or temperature.
How Load Affects Engine Noises
•
Engine load can change the intensity of the noise.
•
The noise may only occur or be more noticeable under a heavy load
•
For example, a bearing with excessive clearance may not create a
noise at idle, but will knock when in gear.
How Temperature Affects Engine Noises
•
Some noises may only occur when the engine is either cold or at
operating temperature.
•
Some clearance-related noises will decrease in intensity when the
engine warms-up and the engine components expand, taking up the
clearance.
•
Lubrication concerns may only appear when the engine is at operating
temperature.
•
Carbon in the cylinder will generally only cause noise when the engine
is cold and it goes away when the engine warms-up.
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2002 General Motors Corporation
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7-16
Top Engine Cleaner
•
Student Workbook
Used to clean carbon deposits from internal engine components.
Does not require engine disassembly.
•
Start the engine and allow it to reach operating temp.
ASE 1 - Engine
Repair
•
With engine idling, disconnect PCV hose from PCV valve and slowly
spray top engine cleaner into hose.
Module 7 - General
Engine Diagnosis
•
Raise engine speed to approx. 2000 rpm and when white smoke is
coming out of exhaust, shut off engine.
•
Let cleaner work for at least 20 minutes.
•
Start engine and increase speed to 2000 RPM until exhaust is no
longer white. This will remove the cleaner.
•
Remember to change oil; cleaner could contaminate it.
•
If the noise was result of carbon, this should remove it. If the noise is
still present, perform additional diagnostics.
Figure 7-2, Top Engine Cleaner
Notice:
There has been a lot of concern about carbon build-up recently and there
are bulletins related to this topic. Make sure you check for bulletins before
performing service. Most times, the bulletins have procedures that were
created as a result of working and testing on vehicles with the concern.
Upper Engine Faults
As with any diagnosis, do the easiest things first. Here are examples of
some external engine faults that could create what may sound like an
upper engine noise.
The first area is accessories. They can create a variety of noises, but if
there is an engine noise, take a few minutes to make sure it's not related
to the accessories.
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7-17
Accessories
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-3, Accessory Drive Belt
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7-18
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-4, Generator
Figure 7-5, Power Steering Pump
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2002 General Motors Corporation
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7-19
In addition to the accessory system there are several other areas that
should be checked that are external to the engine.
Student Workbook
Loose spark plug:
ASE 1 - Engine
Repair
•
Changing pressure inside the cylinder pushes and pulls the spark
plug against the threads of the cylinder head.
•
This causes a metal-to-metal clicking noise.
•
A loose spark plug may be caused by damaged threads, requiring
thread repair.
•
Remember, spark plug threads in aluminum cylinder heads are
frequently damaged when removing them with the engine hot.
Module 7 - General
Engine Diagnosis
Exhaust leak:
•
Unmuffled exhaust pulses can escape through leaks.
•
This can cause a ticking noise.
Internal Components
Primary Areas for Upper Engine Noises
•
Upper valve train
•
Timing chains
The upper valve train is any component that is being driven by the
camshaft or camshafts. To help isolate the source of the noise, use
chassis ears or a stethoscope.
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2002 General Motors Corporation
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7-20
Valve Train Noise Isolation
•
Use the wooden handle of a hammer and place it on the rocker arms.
•
Requires engine to run with valve covers removed. So, make sure oil
does not drip on any hot surfaces, and keep body parts and clothing
away from moving components.
•
Using the wooden handle against the rocker arms removes the
clearance in the valve train. If there is noise caused by excessive
clearance it should go away when placing tension on rocker arm.
•
You'll have to do this to each rocker arm to determine which valve train
component is creating the noise.
•
Check both sides of rocker arm. First take the clearance out of valve
side then out of the camshaft side.
•
If valve train noise goes away or is reduced when handle is placed on
valve side, check valve clearance, rocker arm and valve components
for damage.
•
If noise reduces or goes away when the handle is placed on camshaft
side, check rocker arm, pushrod, lifter and camshaft for damage.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-6, Valve Train Noise Isolation
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2002 General Motors Corporation
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7-21
Inspections for the Various Components
Checking Valve Clearance
•
Start by checking the valve clearance:
– If there is excessive clearance, determine what is causing it. This
may include checking the camshaft lobes.
– If the clearance is OK, start checking for indications of insufficient
lubrication.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
– If the lubrication isn't the cause, check for carbon on the valves and
for valve damage.
– If the valve clearance is incorrect, inspect for several things,
starting with the easier checks.
Figure 7-7, Checking Valve Clearance
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7-22
RockerArm
•
Student Workbook
Loose and/or worn rocker arm and attachments:
– Inspect for damage at the arm, stud, nut or bolt.
– Check the torque to make certain it was torqued to specification.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-8, Rocker Arm Inspection
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2002 General Motors Corporation
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7-23
Valve Lifter
•
Student Workbook
Worn or dirty valve lifters or Stationary Hydraulic Lash Adjusters
(SHLAs):
– Inspect for lifter plungers that will not move and debris in the
general area of the lifter.
•
Bent or damaged push rods:
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
– Inspect for damage at the push rod ends.
Figure 7-10, Valve Lifter Inspection
Inspecting for a Bent Push Rod
•
Roll push rod on a flat surface to detect bent condition.
•
If it doesn't roll smoothly it's bent.
•
A bent push rod is often an indication of a stuck component (like a
valve) or an engine over speed condition.
Figure 7-11, Push Rod Inspection
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7-24
Valve Retainer (Exhaust Only)
•
Worn and/or damaged valve retainers:
•
Inspect for wear, cracks and metal spalling.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Valve Spring
Inspection points:
•
Broken valve springs:
•
Inspect for cracks; these can weaken the spring.
•
Inspect for damaged retainers, these can mis-position the valve, or in
the worst case, allow valve-to-piston contact.
While inspecting components, check for evidence of insufficient
lubrication. This can cause components to prematurely wear and create
clearance concerns.
Inspection for a lubrication concern:
•
Inspect for overheating conditions.
•
Discoloration and metal spalling.
•
If a lubrication concern is suspected, check oil circuits and oil pump
operation.
Valve Guide
Inspection points:
•
Inspect for cracks, internal wear and metal scoring.
•
Check to see if the valve can be opened by rotating the crankshaft.
•
Remember, a stuck valve generally causes damage somewhere else
in the valve train. Something has to give.
Overhead Valve
•
Rock the valve back and forth to determine if the valve guide or stem is
worn.
•
To prevent the valve from dropping into the cylinder with the valve
spring and retainer removed, apply air pressure to the cylinder. Use
the appropriate tools specified in service information.
•
Then rock the valve to determine if there is excessive clearance
between the valve guide and stem.
If there is a valve or guide concern, most likely the cylinder head will have
to be removed for further diagnosis. The only way around this is to use a
Boroscope.
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2002 General Motors Corporation
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7-25
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-11, Overhead Valve Inspections
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2002 General Motors Corporation
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7-26
Valve
Student Workbook
Inspection points:
•
Worn valve stems:
– Inspect for cracks, breaks, overheating, pitting and metal spalling.
– Bent (roll the stem on a flat surface).
•
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Carbon on the valve can also cause noise.
– Remember, carbon related noise generally goes away when the
engine heats up.
– If you suspect carbon, use the top engine cleaner before
disassembling the engine.
Boroscope Operation
•
The tool is basically a small video camera that can be inserted through
the spark plug hole or just about any other engine hole for inspections.
•
It has a light on the end for illumination.
•
An eye piece allows you to see and guide the Boroscope.
•
You can see inside the engine without disassembly.
If there is a Boroscope in your shop, this can be a very useful tool to get
inside the cylinder and the head for inspections. This tool can be ordered
through GM Tool and Equipment.
Figure 7-12, Boroscope
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2002 General Motors Corporation
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7-27
Detonation
Student Workbook
•
Detonation can also cause an upper engine ticking noise.
•
It can cause or be caused by mechanical faults.
•
OBD II has been designed to detect misfire conditions like detonation.
•
Some detonation concerns could be caused by fuel.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Camshafts
A worn or damaged camshaft can cause excessive clearance in the valve
train. There are procedures in the service information called "Camshaft
and Bearings Cleaning and Inspection" which will lead you through the
checks for the camshaft.
Types of inspections:
•
Check lobes for wear and signs of lube starvation.
•
Increased clearance between the camshaft lobes and lifters can create
a clicking noise as camshaft turns.
•
Also check bearings and retainers.
Balance Shaft
The balance shaft can cause a detonation/rattle noise that is most
noticeable under a slight load.
Inspection points:
•
Damaged bearings, broken balance shaft or worn balance shaft
sprocket teeth.
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2002 General Motors Corporation
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7-28
Timing Chain
Student Workbook
Inspection points related to the timing chain:
Worn or broken timing chain and/or sprocket teeth:
•
Check for chain slack, missing teeth, cracks and damaged chain.
•
Timing chain contacting cover.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
– A loose timing chain can contact the cover and create a noise.
•
If excessively loose, the noise can be similar to a lower engine rodbearing knock.
•
Worn timing chain tensioners, shoes and guides:
– Look for tensioner that does not move freely and check for wear
into components.
Figure 7-13, Timing Chain
©
2002 General Motors Corporation
All Rights Reserved
7-29
Lower Engine Noise
External Malfunctions
Student Workbook
ASE 1 - Engine
Repair
Crankshaft Balancer
Inspection points:
Loose or damaged crankshaft balancer:
•
Check bolt torque
•
May cause low oil pressure on some engines
•
Keyway sheering
Module 7 - General
Engine Diagnosis
Inspection points for deterioration:
•
Broken balancer can react incorrectly to the power pulses and rattle.
Loose or damaged engine flywheel:
•
Inspect for loose bolts to crankshaft and cracks.
•
Both can cause a knock noise most noticeable at idle or no load.
•
A cracked flywheel can be mistaken for a rod or main bearing noise.
•
A damaged flywheel can create a knock noise during engine torque
changes on deceleration
Figure 7-14, Flywheel Inspection
©
2002 General Motors Corporation
All Rights Reserved
7-30
Torque Converter
Student Workbook
Inspection points:
•
Loose torque converter bolts:
– Inspect for loose or missing bolts or nuts.
– Check for abnormal elongated holes in the flywheel.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
– Loose bolts will allow the engine power pulses to knock the
flywheel against the converter bolts.
– The noise is most noticeable at idle or no load.
Figure 7-15, Torque Converter/Flywheel Inspection
A loose or cracked flywheel will produce an irregular thud or click. To test
for a loose or cracked flywheel, operate the vehicle at approximately
20 mph and shut off the engine. If a thud is heard, the flywheel may be
loose or damaged. This type of thud is loudest on deceleration.
Loose torque converter-to-flywheel or flywheel-to-crankshaft bolts will
sound similar to bearing knock. This condition produces several raps
during quick acceleration on a free running engine. Depending on the idle
smoothness, when the transaxle is in gear, the noise may or may not
appear.
Check the torque converter-to-flywheel and flywheel-to-crankshaft bolts
before attempting to investigate any bearing related knock.
©
2002 General Motors Corporation
All Rights Reserved
7-31
Notice:
Student Workbook
Be sure the converter-to-flywheel bolts are not too long. Converter bolts
that are too long may dimple the torque converter clutch apply surface
causing a shudder condition.
ASE 1 - Engine
Repair
Pan Damage
Module 7 - General
Engine Diagnosis
Also check the oil pan for external damage. If the pan is damaged, this
could indicate other concerns inside the pan, which could restrict
lubrication.
Pan Damage Can Cause:
•
Pan contact with the suction screen.
•
Pickup tube damage.
•
Oil pump damage.
•
Engine block damage.
Also check the oil filter. Some aftermarket filters do not have the correct
specifications and can restrict flow and allow drain back.
Detonation and Fuel
Fuel can be related to engine noises:
•
Wrong grade or contaminated fuel can cause detonation and knock
noises.
•
Higher octane than needed has also caused carbon concerns since
the high-octane fuel is designed to burn slower.
•
The benefit of high octane is that it reduces ping in high compression
engines.
•
However, if the engine is generally operated for only short trips and is
not allowed to reach operating temperature, the slow burning fuel can
cause carbon build up.
•
Since the engine is not given an opportunity to burn off the carbon, it
builds up to a point where it can cause noise and must be removed.
©
2002 General Motors Corporation
All Rights Reserved
7-32
Internal Causes of Lower Engine Knock
Piston Malfunctions
Checks that can help isolate piston noises:
Excessive piston-to-cylinder bore clearance:
•
This can cause a condition known as piston slap.
•
Usually caused by undersized or improperly shaped piston or an
oversized bore.
•
Most noticeable when the engine is cold, decreases or stops as the
engine warms up.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-16, Piston-to-Cylinder Bore Clearance Measurement
©
2002 General Motors Corporation
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7-33
Excessive piston pin-to-bore clearance:
•
Excessive clearance is generally not affected by load.
•
Excessive clearance can cause a double knock during idle.
•
Piston pins must be centered in the connecting rod pin bore during
assembly.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-17, Excessive Piston Pin-to-Bore Clearance
©
2002 General Motors Corporation
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7-34
Excessive connecting rod bearing clearance:
•
•
Student Workbook
Excessive clearance is generally load sensitive; intensity increases
with load.
The metal-to-metal contact caused by loose components will create a
knock during power pulses.
In addition to these checks, there are several things you should look for
when the knock is related to a piston.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-18, Connecting
Rod Bearing Clearance
Measurement
Additional piston component inspections:
•
Cracked, burnt or scored pistons.
•
Carbon between piston and wall.
– Generally creates a ticking noise.
– The noise will usually go away when the engine reaches normal
operating temperature.
– Top engine cleaner used to remove carbon.
•
Many pistons must be installed with the mark or dimple on the top of
the piston facing the front of the engine.
– Always follow installation procedures in the service information.
If you suspect that a piston has been installed incorrectly, either
disassemble the engine or use a Boroscope.
©
2002 General Motors Corporation
All Rights Reserved
7-35
Crankshaft Bearing Clearance
Student Workbook
Characteristics of crankshaft bearing knock:
This knock noise generally cannot be isolated to a particular cylinder.
It can vary in intensity or may disappear at times, depending on engine
load.
The bearing clearance checking procedure can be used to determine if
there is excessive clearance. This procedure is also used for selecting
bearings.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-19, Main Bearing Clearance Management
Noise at Startup that Goes Away
•
Oil filter
•
Damaged/faulty oil filter bypass valve
•
Incorrect viscosity oil
•
Worn crankshaft thrust bearing
•
High valve lifter/SHLA leak down
Remember, piston slap and carbon can also cause a noise at startup that
goes away shortly thereafter.
Misfire
There is a difference between a true misfire and a mechanical fault that
can cause the PCM to detect a misfire:
•
Mechanical faults can produce a misfire DTC.
•
A misfire is lack of combustion in the cylinder.
•
On most newer engines, the PCM will store a misfire DTC.
©
2002 General Motors Corporation
All Rights Reserved
7-36
Lesson 3: Base Engine Misfire Test
Introduction
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose base engine misfires.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
•
Identify the cause of an engine misfire.
Base Engine Misfire Procedure
Engine performance diagnosis procedures are covered in Engine Controls
and should be consulted for diagnosis of any Driveability, Emissions, or
Malfunctioning Indicator Lamp (MIL) concerns. The following diagnosis
covers common concerns and possible causes. When the proper
diagnosis is made, the concern should be corrected by adjustment, repair
or replacement as required. Refer to the appropriate section of the service
manual for each specific procedure.
This diagnostic procedure will assist in engine misfire diagnosis due to a
mechanical concern such as a faulty camshaft, worn or damaged bearings
or bent pushrod. This procedure will not isolate a crossed injector wire,
faulty injector or any other driveability component failure that may cause a
misfire.
The Powertrain On-Board Diagnostic System checks must be performed
first. When using this procedure to make a Base Engine Misfire diagnosis,
begin with the preliminary information below and then proceed to the
specific category.
Preliminary
1. Perform DTC P0300 before proceeding with Base Engine Misfire
Diagnosis information. DTC P0300 will assist in determining which
cylinder or cylinders are misfiring.
2. Perform a visual inspection for the following:
•
A loose or improperly installed engine flywheel or crankshaft
balancer.
•
Worn, damaged, or misaligned accessory drive system
components.
3. Listen to the engine for any abnormal internal engine noises.
©
2002 General Motors Corporation
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7-37
4. Inspect the engine for acceptable oil pressure. Refer to Oil Pressure
Diagnosis and Testing.
Student Workbook
5. Verify if the engine has excessive oil consumption. Refer to Oil
Consumption Diagnosis.
ASE 1 - Engine
Repair
6. Verify if the engine has coolant consumption.
Module 7 - General
Engine Diagnosis
7. Perform a compression test on the engine. Refer to Engine
Compression Test.
Intake Manifold Leaks
An intake manifold that has a vacuum leak may cause a misfire. Inspect
for the following:
•
Improperly installed or damaged vacuum hoses.
•
Loose throttle body.
•
Faulty or improperly installed intake manifold and/or gaskets.
•
Loose Exhaust Gas Recirculation (EGR) Valve pipe or damaged or
missing O-ring seal.
•
Cracked or damaged intake manifold; Inspect the areas between the
intake runners.
•
Improperly installed Manifold Absolute Pressure (MAP) sensor. The
sealing grommet of the MAP sensor should not be torn or damaged.
•
Improperly installed throttle body or damaged gasket.
•
Warped intake manifold.
•
Warped or damaged cylinder head sealing surface.
©
2002 General Motors Corporation
All Rights Reserved
7-38
OBD System Check
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
©
2002 General Motors Corporation
All Rights Reserved
7-39
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
•
Steps 1 & 2: Checks ability of scan tool to power up & communicate.
•
Step 3: Checks engine start/idle.
•
Step 4: Checks for stored DTCs.
•
Step 5: Captures stored Powertrain DTC information.
•
Step 6: Does scan tool display U-type codes?
•
Step 7: Does scan tool display DTC P0601, P0602, P0604 or P0606?
•
Step 8: Does scan tool display DTC P0562, P0563, P1637 or P1638?
Figure 7-20, Tech 2 with DTC P0300
©
2002 General Motors Corporation
All Rights Reserved
7-40
DTC P0300 Engine Misfire Diagnosis Chart
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
©
2002 General Motors Corporation
All Rights Reserved
7-41
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
©
2002 General Motors Corporation
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7-42
Misfire Counter Check (Single)
•
Misfire counter for cylinder #3 is increasing, while the other counters
are stable.
•
Cylinder #3 is misfiring since the counters are increasing.
•
Also, we suspect the #1 misfire counter is increasing since it is the
next cylinder in the firing order.
•
This can often occur, since the non-misfiring cylinder cannot increase
the RPM rapidly enough to compensate for the lag created by the
previous cylinder.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-21, Misfire Counter Check
©
2002 General Motors Corporation
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7-43
Test Lamp J 26792 / ST 125 Spark Testing
J 26792/ST 125 Spark Tester results:
•
Spark tester showed spark at the cylinder
•
The spark plug appeared to be visually OK
•
The misfire did not move when we swapped spark plugs
•
At Step 6 we will use the injector test lamp
•
With ignition OFF, remove the connector for the #3 cylinder and install
the test lamp
•
For this vehicle, we will use J 34730-405
•
Start the engine and see what happens
•
At Step 7 we will be using the J 26792/ST 125 to check spark on #3
cylinder
•
Now, install J 26792/ST 125 spark tester; make sure it is connected to
a good ground
•
Start the engine
•
It appears OK, so let's move to Step 9 and look at the spark plug
•
Spark plugs appear okay
•
Let's move to Step 10 and swap the spark plugs
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
J 26792/ST 125 Spark Tester results:
•
Spark tester showed spark at the cylinder
•
The spark plug appeared to be visually OK
•
The misfire did not move when we swapped spark plugs
Injector Coil Test
A "No" answer at Step 10 sends you to perform the fuel injector coil test.
Results of Injector Coil test:
•
The results we have are within specifications
•
The chart then directs us to Symptoms
•
However, P0300 chart said that if injector coil test procedure checks to
be OK, refer to Base Engine Misfire Diagnosis
The results are within specification, so we move on to the base engine
misfire.
©
2002 General Motors Corporation
All Rights Reserved
7-44
Base Engine Misfire Table
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
We performed Steps 1-6 of the Preliminary Checks and no issues
were found.
We move on to Step 7, performing a static compression test.
©
2002 General Motors Corporation
All Rights Reserved
7-45
Lesson 4: Static Compression Test
Introduction
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine mechanical concerns utilizing the static
compression test.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
•
Identify the condition of the engine's piston rings, valves and head
gasket(s).
Static Compression Test
To prepare for an engine compression test:
1. Charge the battery if the battery is not fully charged.
2. Disable the ignition system.
3. Disable the fuel injection system.
4. Remove all the spark plugs.
5. Block the throttle plate wide open.
6. Start with the compression gauge at zero and crank the engine through
four compression strokes (four puffs).
7. Make the compression check for each cylinder. Record the reading.
8. If a cylinder has low compression, inject approximately 15 ml (one
tablespoon) of engine oil into the combustion chamber through the
spark plug hole. Recheck the compression and record the reading.
9. The minimum compression in any one cylinder should not be less than
70 percent of the highest cylinder. No cylinder should read less than
690 kPa (100 psi). For example, if the highest pressure in any one
cylinder were 1035 kPa (150 psi), the lowest allowable pressure for
any other cylinder would be 725 kPa (105 psi) (1035 x 70% = 725)
(150 x 70% = 105).
©
2002 General Motors Corporation
All Rights Reserved
7-46
•
Normal — Compression builds up quickly and evenly to the specified
compression for each cylinder.
Student Workbook
•
Piston Rings Leaking — Compression is low on the first stroke.
Compression then builds up with the following strokes but does not
reach normal. Compression improves considerably when you add oil.
ASE 1 - Engine
Repair
•
Valves Leaking — Compression is low on the first stroke. Compression
usually does not build up on the following strokes. Compression does
not improve much when you add oil.
•
If two adjacent cylinders have lower than normal compression and
injecting oil into the cylinders does not increase the compression, the
cause may be a head gasket leaking between the cylinders.
©
2002 General Motors Corporation
All Rights Reserved
Module 7 - General
Engine Diagnosis
7-47
Lesson 5: Running Compression Test
Introduction
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine mechanical concerns utilizing the running
compression test.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
Identify the engine's ability to fill and evacuate the cylinder to produce the
proper engine output during idle and loaded conditions.
How to Perform a Running Compression Test
1. Start with a normal ("static") compression test. To eliminate rings,
valves, holes in pistons, that sort of thing. A normal cylinder balance
test is also helpful (so you know which, if any, cylinder is presenting a
problem). Engine should be warm.
2. Put all spark plugs but one back in. Ground that plug wire to prevent
module damage. Disconnect that injector on a port fuel system.
3. Put your compression tester into the empty hole. The test can be done
without a Schrader valve, but most people recommended leaving the
valve in the gauge and "burping" the gauge every 5-6 "puffs."
4. Start the engine and take a reading. Write it down.
5. Now snap the throttle for a "snap acceleration" reading. Reading should
rise. Write it down.
Notice:
Don't use the gas pedal for this snap acceleration. The idea is to manually
open then close throttle as fast as possible without speeding up the
engine. This forces the engine to take a "gulp" of air.
6. Now, write down your readings for at least the bad cylinder (if there is a
single bad cylinder) and maybe 2-3 good ones.
©
2002 General Motors Corporation
All Rights Reserved
7-48
Make a chart like this:
Student Workbook
CYL
STATIC COMPR
IDLE - RUNNING
COMPR - SNAP
Cyl 1
150
75
125
Cyl 2
175
80
130
Cyl 3
160
75
120
Cyl 4
160
80
125
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
7. Analysis:
Running compression at idle should be 50-75 psi (about half cranking
compression). Snap throttle compression should be about 80% of
cranking compression.
Sample 1 - Restricted Exhaust
CYL
STATIC COMPR
IDLE - RUNNING
COMPR - SNAP
Cyl 1
150
75
180
If snap measurements are higher than 80% of cranking measurements,
look for restricted exhaust on that cylinder - such as worn exhaust cam
lobe, or collapsed lifter. Or, if these are all high, look for a clogged catalytic
converter.
©
2002 General Motors Corporation
All Rights Reserved
7-49
Lesson 6: Cylinder Leakage Test
Introduction
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine mechanical concerns utilizing the cylinder
leakage test.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
The cylinder leakage test may be used in conjunction with the engine
compression test to isolate the cause of leaking cylinders.
Cylinder Leakage Test - Testing Procedure
Tools Required - J 35667-A Cylinder Leakdown Tester
With the use of air pressure, a cylinder leakage test will aid in the
diagnosis. Use the cylinder leakage test in conjunction with the engine
compression test in order to isolate the cause of leaking cylinders.
Caution:
Before servicing any electrical component, the
ignition key must be in the OFF or LOCK position
and all electrical loads must be OFF, unless
instructed otherwise in these procedures. If a tool
or equipment could easily come in contact with a
live exposed electrical terminal, also disconnect
the negative battery cable. Failure to follow these
precautions may cause personal injury and/or
damage to the vehicle or its components.
©
2002 General Motors Corporation
All Rights Reserved
7-50
1. Disconnect the negative battery cable.
2. Remove the spark plugs. Refer to Spark Plug Replacement in Engine
Controls.
Student Workbook
3. Install the J 35667-A
ASE 1 - Engine
Repair
4. Measure each cylinder on the compression stroke, with both valves
closed.
Module 7 - General
Engine Diagnosis
Notice:
Hold the crankshaft balancer bolt in order to prevent piston movement.
5. Apply air pressure, using the J 35667-A. Refer to the manufacturer's
instructions.
6. Record the cylinder leakage readings for each cylinder.
Notice:
Normal cylinder leakage is from 12 to 18 percent. Make a note of any
cylinder with more leakage than the other cylinders. Any cylinder with 30
percent leakage or more requires service.
7. Inspect the 4 primary areas in order to properly diagnose a leaking
cylinder.
8. If air is heard from the intake or exhaust system, perform the following
procedure:
Remove the valve rocker arm cover of the suspect cylinder head.
Ensure that both valves are closed. Inspect the cylinder head for a
broken valve spring. Remove and inspect the suspect cylinder head.
Refer to Cylinder Head Cleaning and Inspection.
9. If air is heard from the crankcase system at the crankcase (oil filler
tube), perform the following procedure:
Remove the piston from the suspect cylinder. Inspect the piston and
connecting rod assembly. Refer to Piston, Connecting Rod, and
Bearings Cleaning and Inspection. Inspect the engine block. Refer to
Engine Block Cleaning and Inspection.
©
2002 General Motors Corporation
All Rights Reserved
7-51
10. If bubbles are found in the radiator, perform the following procedure:
Remove and inspect both cylinder heads. Refer to Cylinder Head
Cleaning and Inspection. Inspect the engine block. Refer to Engine
Block Cleaning and Inspection.
11. Remove the J 35667-A.
12. Install the spark plugs. Refer to Spark Plug Replacement in Engine
Controls.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
13. Connect the negative battery cable. Refer to Battery Negative Cable
Disconnect/Connect Procedure in Engine Electrical.
Figure 7-22, Cylinder Leakdown Tester
©
2002 General Motors Corporation
All Rights Reserved
7-52
Lesson 7: Restricted Exhaust Test
Student Workbook
Introduction
ASE 1 - Engine
Repair
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine mechanical concerns utilizing the
restricted exhaust test.
Module 7 - General
Engine Diagnosis
Objective
Identify an engine mechanical concern related to a restricted exhaust
system.
Restricted Exhaust Diagnostic Chart
©
2002 General Motors Corporation
All Rights Reserved
7-53
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
©
2002 General Motors Corporation
All Rights Reserved
7-54
Lesson 8: Vacuum Test
Introduction
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine mechanical concerns utilizing the vacuum
test.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
Describe the procedure to check engine vacuum and identify the
source(s) of incorrect vacuum readings.
Vacuum Test
The intake stroke of the piston creates a vacuum in the manifold. Vacuum
is any pressure lower than the atmospheric pressure. Monitoring the
manifold vacuum is a good indicator of the engine's ability to run
efficiently. Typical engine vacuum is a steady reading between 15 and 22
inches of mercury with the engine at normal operating temperatures, idle,
and in drive.
Vacuum Test Limitations
The amount of vacuum formed in the manifold depends on several things.
•
First, the cylinders must be sealed. If a cylinder has high leakage, it
will not produce sufficient vacuum to draw in the air/fuel mixture.
•
If the manifold is not sealed, vacuum will be lower than normal.
•
Vacuum hoses and accessories may leak, causing lower manifold
vacuum.
•
When the throttle plate is open and atmospheric pressure enters the
manifold, vacuum is lower.
•
If the engine has higher compression, it will have 1 to 2 inches of
mercury higher vacuum.
•
For every 1,000 feet of altitude above sea level, vacuum will be
lowered by 1 inch of mercury.
•
A high lift cam or considerable valve overlap will produce a slightly
lower, erratic needle reading on the gauge.
•
Vacuum changes with load, so operating accessories when monitoring
vacuum will change the readings.
©
2002 General Motors Corporation
All Rights Reserved
7-55
Vacuum Test Results
•
Student Workbook
A needle that fluctuates or drops between 1 and 2 inches of mercury at
idle indicates a burned or leaking valve or a spark plug in one of the
cylinders that is not firing.
•
An irregular needle drop between 1 and 2 inches of mercury indicates
a sticking valve, intermittent spark plug misfire, or rich or lean air/fuel
mixture.
•
If the vacuum gauge indicates normal at idle speed, but has excessive
vibrations at higher RPM, the cause is most likely weak valve springs
or valves sticking in their guides.
•
If the vacuum needle has an excessive vibration at idle speed, but
steadies at higher RPM, check for worn valve guides.
•
If the vacuum gauge needle has an excessive vibration at all RPM, the
problem is a leaky head gasket.
•
If the needle oscillates slowly, or drifts, between 3 and 9 inches of
mercury lower than normal, check for an intake system leak.
•
If the vacuum is normal at idle speed, but drops to near zero and rises
to lower than normal, the problem is a restriction in the exhaust
system.
©
2002 General Motors Corporation
All Rights Reserved
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
7-56
Vacuum Test Diagnosis Chart
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
©
2002 General Motors Corporation
All Rights Reserved
7-57
Lesson 9: Oil Pressure Test
Introduction
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine oil pressure concerns.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Objective
Describe the procedure to check oil pressure and identify the sources of
low oil pressure.
Engine Oil Functions
•
Provides lubrication to moving parts to prevent damage and
overheating.
•
Supplies operating pressure to components like valve lifters and the
camshaft position actuator on the 4200 engine.
•
Cools moving components.
•
Provides sealing and cleaning.
Because the oil performs various functions, sufficient flow must be
provided by the oil system to make certain that sufficient oil is delivered to
engine components.
There are several checks that must be performed to determine if the oil
and the oil system are performing the necessary functions.
Initial Engine Oil Checks
Check the level:
•
If the level is too low, the lubrication system may not be able to provide
sufficient flow.
•
If the fluid is too high, it can be an indicator of contamination (fuel,
water or coolant).
Check the condition:
•
Oil properties degrade over time.
•
Combustion gases escaping past the piston rings can contaminate
the oil.
©
2002 General Motors Corporation
All Rights Reserved
7-58
Check vehicle oil gauge (if equipped):
•
A good initial check of oil is to look at the vehicle oil pressure gauge.
•
However, the gauge may not be as sensitive as a mechanical gauge
connected directly to the system.
There are two important points that you should remember about
engine oil:
•
At 6 psi, the oil pressure light turns on.
•
Normal oil consumption is 1 quart per 2000 miles.
•
During the break-in period, this can be higher.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Oil Pressure Test
•
Before connecting the gauge, perform a few preliminary inspections:
– Check for oil pan damage and look for oil leaks.
– Observe and note abnormal noises.
•
Install the gauge and check pressure using service procedures
– Some applications require special tools
•
Compare gauge readings to specifications
– Check oil pressure cold and hot.
Remember, you can check both the upper end and the lower end for
diagnostic purposes.
Oil Pressure Checking
•
Service procedures generally select pressure tap near oil pump outlet
to provide initial pressure produced by pump.
•
Tells you if pump is operating within specifications, but not what is
happening in other parts of engine.
•
If pump is producing insufficient pressure at this tap, look for
restrictions or leakage in the lower engine circuit.
•
Can also check the pressure further up oil circuit on many engines
when valve train is producing noise but oil pressure near the pump is
correct
•
If there is restriction or leak in the upper valve train circuits, valve train
will have insufficient lubrication. Pressure check this portion of the
circuit for lower pressure. Closely inspect valve train components for
damage.
©
2002 General Motors Corporation
All Rights Reserved
7-59
Oil pressure concerns can be a major cause of engine noises. If the
pressure is low at all times, severe engine damage can occur. However,
some oil pressure conditions can cause a condition where the engine
creates a noise at startup and then goes away shortly after.
There is a table in the service information that will help you identify some
of the root causes of this condition.
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-23, Oil Pressure Checking
Oil Pump with Suction Screen
•
Worn oil pump or debris in the pump
– Creating a restriction or inefficient oil pump operation.
•
Loose oil pump-to-engine bolts
•
Loose, plugged or damaged oil pump screen.
•
Missing or damaged oil pump screen o-ring seal.
•
Damage or leak in the oil pump screen suction tube.
– Allowing air to enter the pump intake
©
2002 General Motors Corporation
All Rights Reserved
7-60
Pressure Regulator Valve
•
Student Workbook
Malfunctioning oil pump pressure regulator valve
– Allowing a bypass and low pressure
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-24, Pressure Regulator Valve Inspection
Oil Gallery Plugs
•
Missing or incorrectly installed oil gallery plug.
•
Cracked, porous or restricted oil galleries.
•
These could be external leaks.
Figure 7-25, Oil Gallery Plugs Inspection
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2002 General Motors Corporation
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7-61
Lesson 10: Engine Speed-Related Vibrations
Student Workbook
Introduction
ASE 1 - Engine
Repair
After completing this unit, the technician will be able to apply concepts and
procedures to diagnose engine speed-related vibrations.
Module 7 - General
Engine Diagnosis
Objective
Describe Engine Speed-Related Vibration Firing Frequencies.
Isolating Vibrations
•
Duplicate the vibration while the vehicle is on an inspection-type hoist
(either a front-end rack or similar hoist that supports the vehicle at curb
height).
•
While the vibration is present, find the area(s) of the vehicle that are
excited or responding to the vibration.
•
Look closely for witness marks due to a rubbing component.
•
Once an area of the vehicle has been pinpointed, the component
should be isolated and the vibration re-evaluated.
•
Firing frequency is a term used to describe the pulses that an engine
creates as it fires each cylinder.
Figure 7-26, Engine Order Vibration Chart
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2002 General Motors Corporation
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7-62
Speed-Related Vibrations
Student Workbook
Vibration concerns can be categorized into two groups:
•
Vehicle Speed
•
Engine RPM
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
The Slow Acceleration Test is used to identify engine or speed-related
concerns.
•
The Neutral Coast-Down Test and Downshift Test should be performed
to help determine which category the vibration belongs.
The Neutral Coast-Down test is used to identify concerns related to
vehicle speed.
•
Eliminates the engine and torque converter as a vibration cause.
•
Concentrates the repair on the tires and wheels, or on the propshaft
and rear (driving) axle based on symptoms.
Figure 7-27, Speed-Related Vibrations
©
2002 General Motors Corporation
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7-63
Notice:
Student Workbook
If the concern is vehicle-speed related only; that it appears at the same
mph regardless of the engine speed, the Neutral Run-Up Test and Brake
Torque Test probably will not apply.
ASE 1 - Engine
Repair
Notice:
Module 7 - General
Engine Diagnosis
The Neutral Run-Up Test and Brake Torque Test are used for engine
speed-related vibrations.
Engine Speed-Related Vibrations
The Downshift Test and Neutral Run-Up Test are used to identify engine
speed related concerns.
Brake Torque Test
Identifies engine-speed-related vibrations not revealed by the Neutral
Run-Up Test.
This test also works for vibrations that are sensitive to engine load or
torque.
•
If the vibration returns at the same rpm, the engine and torque
converter are the most probable causes
•
In some cases, a vibration may be sensitive to torque or engine load
•
These vibrations can be the most difficult to diagnose, and may require
additional testing
The Brake Torque Test identifies engine speed-related vibrations, not
revealed by the Neutral Run-Up Test.
Neutral Run-Up Test
Identifies engine speed-related vibrations.
Use this test whenever customer expresses a concern about vibration at
idle, or as a follow-up to Downshift Test.
©
2002 General Motors Corporation
All Rights Reserved
7-64
Brake Torque Test
Student Workbook
Identifies engine-speed-related vibrations not revealed by the Neutral
Run-Up Test.
This test also works for vibrations that are sensitive to engine load or
torque.
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
Figure 7-28, Engine Speed-Related Vibrations
Do not accelerate against the brakes for longer
than 15 seconds.
Care should be taken not to overheat the engine
or transmission.
Depending on the vehicle design, the engine will
only rev to a certain point under these conditions.
Also, care should be taken during diagnosis
because some disburbances may be created
during brake torque that normally does NOT exist.
©
2002 General Motors Corporation
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7-65
Exercise 7-1
Student Workbook
Read each question carefully and choose the correct response.
1. A compression test is performed on an engine. Technician A states that
the lowest cylinder should NOT be les than 70% of the highest
reading. Technician B states that you should consult service
information for the correct pressure specifications. Which technician is
correct? (3)
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
a. Technician A
b. Technician B
c. Both technicians are correct
d. Neither technician is correct.
2. For a properly running engine, a good vacuum reading should be
______________.
a. 10-14 inches of mercury
b. Steady needle, 17-20 inches of water
c. Steady needle, 17-20 inches of mercury
d. Fluctuating gauge between 15-17 inches of water
3. A diagram shows a vacuum hose connected to “ported vacuum.” This
means the hose should be connected _____________.
a. To the vacuum reservoir tank
b. To the intake manifold
c. Below the throttle plate
d. Above the throttle plate
4. All of the following engine mechanical conditions can be diagnosed
with a leakage test EXCEPT:
a. Burned exhaust valve
b. Cracked or warped head
c. Worn cam lobes
d. Worn piston rings
©
2002 General Motors Corporation
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7-66
5. During a cylinder leakage test you find air coming out around the
cylinder head valve cover. All of the following could be the cause
EXCEPT:
a. Blown head gasket
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
b. Cracked block
c. Warped head
d. Worn piston rings
6. A leakage test on cylinder 3 shows air coming from cylinder 5, and vice
versa. These results mean which of the following?
a. Leakage head gasket
b. Hole in piston 3
c. Leaky exhaust valve
d. Leaky intake valve
7. A customer is concerned because oil is leaking from the middle of their
vehicle engine compartment. The source of the leak cannot be
determined visually. How should the source of the leak be pinpointed?
a. Overfill all the fluids
b. Inspect seals
c. Replace all the seals
d. Use fluorescent dye
8. Which of the following devices is used with dye to help find leaks?
a. Fluorescent light
b. Infrared camera
c. Ultraviolet light
d. Neon light
9. When using the black light and dye method to perform oil leak
detection, the dye will appear _______ under the light.
a. Red
b. Yellow
c. Blue
d. Black
©
2002 General Motors Corporation
All Rights Reserved
7-67
10. The purpose of the oil pump is to ______________.
Student Workbook
a. clean the oil
ASE 1 - Engine
Repair
b. cool the oil
c. pressurize the oil
d. control oil pressure
Module 7 - General
Engine Diagnosis
11. Which of the following is NOT a cause of low or no oil pressure?
a. Improper oil viscosity
b. Low oil level
c. Low cylinder compression
d. Slow idle speed
12. Which of the following can NOT be the cause of low engine oil
pressure?
a. Loose crankshaft balancer bolt
b. Loose oil pump mounting bolts
c. Missing pickup o-ring
d. Broken valve lifters
13. On a V-type engine with dual overhead cams, compression is found to
be low on all cylinders in one bank only. The most likely cause would
be _____________.
a. jumped timing chain
b. incorrect ignition timing
c. leaking head gasket
d. broken crank gear
14. If camshaft timing were incorrect, all of the following might be the result
EXCEPT ___________.
a. no start
b. lack of power
c. possible damage to valves or pistons (depending on the
application)
d. worn camshaft lobes
©
2002 General Motors Corporation
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7-68
15. When verifying camshaft timing, the timing marks should be at which
of the following positions?
a. All at 12 o’clock
b. Pointing at each other
c. Lined up according to service information
d. Ignored, as they are only for use in ignition timing
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
16. Valve train noises occur at _______ speed of the engine.
a. 1/4
b. 1/2
c. 3/4
d. the same
17. When checking the Camshaft position actuator movement,
approximately how much movement should there be?
a. 5-8 mm
b. 10-11 mm
c. 14-15 mm
d. 17-18 mm
18. A customer brings in a 1996 Oldsmobile Aurora with a 4.0L V8. The
customer is concerned because oil is leaking from the middle of the
engine compartment. Which of the following processes should be used
to solve the concern?
a. System verification process
b. Strategy-based diagnostics
c. Testing based diagnostics
d. Strategy verification process
19. A customer brings in a 1996 Oldsmobile Aurora with a 4.0L V8. The
customer is concerned because oil is leaking from he middle of the
engine compartment. Which of the following is the first step?
a. Check bulletins
b. Verify the customer concern
c. Check vehicle history
d. Start OBD system check
©
2002 General Motors Corporation
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7-69
20. A customer brings in a vehicle with an intermittent misfire concern. The
MIL is illuminated. Which of the following is the first step in diagnosing
this concern using a strategy based diagnostic process?
a. Verify concern
b. Check service diagnostics
c. Verify bulletins
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
d. Conduct preliminary checks
21. A customer brings in a 1999 Cadillac Eldorado with a 4.6L V8 VIN Y
ROP Code LD8, concerned because it misfires at all times. The MIL is
illuminated. All of the following are quick checks EXCEPT:
a. Checking for loose or missing plug wire
b. Looking for damaged coil
c. Listening for engine noises
d. Checking for vehicle history
22.After performing an engine vacuum and a compression test, the test
results are reviewed and oil is added to cylinders 3 and 5. If the
compression remains the same, which of the following tests is
performed next?
a. Compression test
b. Cylinder leakage test
c. Fuel pressure test
d. Oil pressure test
23. A compression test shows that one cylinder is too low. A cylinder
leakage test shows that there is too much leakage. During the test, air
could be heard coming from the tailpipe. Which of the following could
be the cause?
a. Broken piston ring
b. Blown head gasket
c. Leaking exhaust gasket
d. Leaking exhaust valve
©
2002 General Motors Corporation
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7-70
24. An irregular thud or click loudest on deceleration is most likely related
to the ____________.
a. main bearings
Student Workbook
ASE 1 - Engine
Repair
b. flywheel
c. valve train
d. harmonic balancer
Module 7 - General
Engine Diagnosis
25. In engine noise diagnosis, noises synchronized to one-half the engine
speed are normally associated with the __________.
a. main bearings
b. connecting rod bearings
c. pistons
d. valve train
26. A high frequency light-knocking sound occurring at the same intensity
regardless of engine load is related to the _______________.
a. flywheel
b. connecting rod bearings
c. main bearings
d. timing chain and sprocket
27. Top engine cleaner is the recommended GM cleaner for which of the
following conditions:
a. Leaking oil seals
b. Carbon build up
c. Coolant system leaks
d. Defective head gasket
28. When removing carbon build up, the top engine cleaner should be
allowed to work inside the engine for at least ________ minutes,
before starting the engine to remove the cleaner:
a. 5
b. 10
c. 15
d. 20
©
2002 General Motors Corporation
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7-71
29.The injector test lamp tests which of the following:
Student Workbook
a. The mechanical side of the injector
b. The fuel pump
c. The PCM and harness
d. The fuel pressure regulator
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
30. A customer is concerned about a knocking noise in the front of their
vehicle on start up. The first step of the SBD process is __________.
a. verify the concern
b. preliminary checks
c. check vehicle history
d. check bulletins
31. In reference to low or no oil pressure, Technician A says that it could
be caused by worn main bearings. Technician B says that worn rings
will cause the same. Which technician is correct?
a. Technician A
b. Technician B
c. Both technicians are correct
d. Neither technician is correct
32. During which of the following engine operating conditions will carbon
build up cause a noise concern?
a. Cold engine operation
b. Engine overheating condition
c. Normal operating conditions
d. All engine operating conditions
33. Which of the following noises would usually be associated with a
balance shaft concern?
a. Rattle noise
b. Whine
c. Knock
d. Growl
©
2002 General Motors Corporation
All Rights Reserved
7-72
34. A damaged flywheel will usually create a knocking noise during which
of the following conditions:
a. acceleration
Student Workbook
ASE 1 - Engine
Repair
b. deceleration
Module 7 - General
Engine Diagnosis
c. idle
d. part throttle cruise
35. Which of the following is a cause of low oil pressure?
a. Too much oil
b. Broken piston oil ring
c. Plugged oil pump pickup screen
d. Oil pan leak
36. A technician is measuring engine vacuum on an engine. The readings
are 20 inches of vacuum at idle and 10 inches of vacuum at 2000
RPM. This would indicate _______________.
a. late valve timing
b. restricted exhaust
c. restriction in air intake system
d. a vacuum leak at the intake manifold
37. A plugged catalytic converter will cause a vacuum gauge to _______.
a. read a steady 16 inches at idle
b. fluctuate between 16 and 21 inches at idle
c. read a steady 25 inches at idle
d. read a gradual loss of vacuum
38. When checking engine vacuum, idle has 15 inches and when
increasing RPM’s, vacuum steadily drops off and engine stalls. This
means the _____________.
a. catalytic converter is restricted
b. muffler has been replaced with test pipe
c. vacuum reading is normal
d. engine timing is retarded
©
2002 General Motors Corporation
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7-73
39. A vacuum test shows low, but steady vacuum. Which of the following is
the least likely cause?
a. Weak valve springs
b. Leakage around piston rings
c. Late ignition timing
d. Vacuum leak
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
40. For most engines, normal engine vacuum at idle should be _______
inches Hg.
a. 25-29
b. 15-22
c. 7-12
d. 5-7
41. When performing an engine vacuum test, the test shows the needle
fluctuating between 12 and 17 inches Hg. Which of the following tests
should be performed next?
a. Compression test
b. Engine vacuum test
c. Fuel pressure test
d. Leakage test
42. For every _______ feet of altitude above sea level, vacuum will be
lowered by 1 in-Hg.
a. 500
b. 1,000
c. 5,000
d. 10,000
43. While doing a cylinder leakage test, the technician finds air escaping
out the dipstick tube. The most likely cause would be ____________.
a. worn piston rings
b. burned intake valve
c. blown head gasket
d. burned exhaust valve
©
2002 General Motors Corporation
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7-74
44. A car runs rough and backfires through the throttle body. Compression
is checked and one cylinder is low. The most likely cause of the
problem is a/an:
a. faulty intake valve
b. burned exhaust valve
c. EGR valve failure
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
d. blown head gasket
45. During a compression test, you get a reading of 80 PSI dry and
140 PSI wet on the #4 cylinder. All other cylinders are about 145 PSI
wet and dry. Which of these readings most likely indicate a/an:
a. blown head gasket between cylinder #3 and cylinder #4
b. bad intake valve on cylinder #4
c. bad exhaust valve on cylinder #4
d. worn piston ring on cylinder #4
46. During an engine compression test, how many compression strokes
are needed to obtain an accurate reading on the gauge?
a. Four
b. Three
c. Two
d. One
47. An engine compression test indicates compression is low on the first
stroke, and does NOT build up, even with the addition of oil. Which of
the following parts could be the cause of this concern?
a. Valve stem seals
b. Piston rings
c. Valves
d. Intake manifold
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2002 General Motors Corporation
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7-75
48. An engine compression test indicates compression is low on the first
stroke, but builds with successive strokes, especially when oil is
added. Which of the following parts is most likely the cause of this
concern?
a. Valve stem seals
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
b. Piston rings
c. Valves
d. Head gasket
49. When performing an engine compression test, if the compression is
low on the first stroke, does NOT build on successive strokes, and
does NOT increase with oil added, the most likely problem is/are the:
a. Valves
b. Piston rings
c. Intake manifold
d. Valve stem seals
50. During a cylinder leakage test, you notice air escaping past the throttle
plate. This means there is a leak at the __________.
a. Piston rings
b. Intake valve
c. Intake manifold gasket
d. Head gasket
51. During the leakage test, listen for air leakage in all of the following
locations EXCEPT the:
a. Throttle body
b. Tailpipe
c. Crankcase or valve cover
d. Transmission
©
2002 General Motors Corporation
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7-76
52. Which of the following is the MOST likely symptom of a leaky valve
when performing a cylinder leak down test?
a. Hissing in crankcase
b. Bubbles in radiator
c. Hissing in intake or exhaust
d. Hissing at the spark plug hole
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
53. When doing a compression test, all cylinders are found to be low.
Which of the following would be the most likely cause?
a. Advanced ignition timing
b. Burned intake valves
c. Late valve timing
d. Carbon build up in the cylinder
54. A leak in the hose on the bottom radiator tank to the water pump will
allow coolant to leak and:
a. Air to enter
b. The thermostat to fail
c. Increase pressure in cap
d. The hose to fail
55. Technician A says that too high an oil level could cause seepage and
foaming. Technician B says it could cause low crankcase pressure.
Which technician is correct?
a. Technician A
b. Technician B
c. Both technicians are correct
d. Neither technican is correct
56. A common cause for excessive oil burning is a/an ____________.
a. stuck piston rings
b. leaking crankshaft seal
c. clogged engine air cleaner
d. external leak
©
2002 General Motors Corporation
All Rights Reserved
7-77
57. You are performing a cylinder leakage test. Bubbles in the radiator
would indicate ______________________.
a. defective piston rings
b. burned intake valve
c. a leaking intake manifold gasket
d. a blown head gasket
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
58. The primary cause of an overheating problem is ________________.
a. thermostats
b. loss of coolant
c. defective water pumps
d. incorrect coolant mixture
59. When using an outside micrometer with a Vernier scale, the most
precise measurement is obtained from the Vernier. To read the scale,
identify the Vernier number that is most perfectly _____________.
a. aligned with any scale mark on the barrel
b. aligned with the Vernier pointer on the thimble
c. aligned with any scale mark on the thimble
d. between any two scale marks on the thimble
60. Which of the following must be reset on the torque angle meter before
tightening each fastener?
a. Angle zero pad
b. Reset angle pad
c. Operate/set alarm pad
d. Torque/angle pad
61. Which of the following tools is used to measure crankshaft endplay?
a. Torque angle meter
b. Dial indicator
c. Micrometer
d. Telescoping gauge
©
2002 General Motors Corporation
All Rights Reserved
7-78
62. One of the reasons that piston rings wear a deeper groove at the top of
the cylinder than at the bottom is that the ______________.
a. connecting rod angle is greater
b. combustion pressure is higher at the top
c. heat softens the upper wall
d. cooling system is less effective there
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
63. The thrust surfaces of a cylinder are _____________ to the piston pin.
a. parallel
b. vertical
c. horizontal
d. perpendicular
64. When removing valve springs, which of the following should be done to
prevent the valve from dropping into the cylinder?
a. Grasp valve with valve stem key
b. Compress valve locks using valve lock compressor
c. Insert valve stem retaining pin
d. Apply air pressure to the cylinder
65. Which of the following is a thread-locking compound and is applied to
the insert OD threads?
a. General Motors P/N 1052864
b. Loctite® 277
c. General Motors Cleaner P/N 12346139
d. WD-40®
66. Engine blocks may be distorted if head bolts are tightened without the
use of a _________ wrench.
a. box
b. rachet
c. socket
d. torque
©
2002 General Motors Corporation
All Rights Reserved
7-79
67. With the camshaft and crankshaft gears aligned correctly, the piston on
Number 1 cylinder is located ______________.
a. on valve overlap
b. BDC on exhaust stroke
c. TDC on compression stroke
d. BDC on power stroke
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
68. Push rods should be checked for ______________.
a. straightness
b. adjustment
c. clearance
d. rotatability
69. Excessive valve guide clearance can be corrected by all of the
following EXCEPT ______________.
a. by knurlizing
b. with valve guide installation
c. with an oversized valve stem
d. with an undersized valve stem
70. The crankshaft is held in the engine block by the ______________.
a. rod caps
b. main bearing caps
c. main bearing journals
d. harmonic balance
71. Two types of rear main-bearing oil seal materials are _____________.
a. neoprene and leather
b. neoprene and rope
c. #2 Permatex and RTV
d. rubber and anaerobic
©
2002 General Motors Corporation
All Rights Reserved
7-80
72. In which groove(s) is the oil ring located?
Student Workbook
a. Bottom
ASE 1 - Engine
Repair
b. Middle
c. Top
Module 7 - General
Engine Diagnosis
d. All grooves
73. Which one of the following cleaning methods uses live microbes to
clean components?
a. Bio-remediating
b. Sand blasting
c. Acid bath
d. Sonic vibration
74. If a bio-remediating aqueous parts washer is NOT used for more than
two weeks, it may be necessary to change the filter pad in order to
_________.
a. provide a fresh supply of microbes
b. remove excess oil and grease
c. provide fresh supply of rust inhibitor
d. prevent sediment from clogging the circulating pump
75. An engine failure has caused metal contamination of the oil. Which of
the following must be replaced?
a. Regulating valve
b. Oil cooler
c. Relief valve
d. Nothing needs to be replaced
76. The proper way to clean a cylinder head is to use _________.
a. aluminum oxide disks
b. solvent
c. a plastic scraper
d. air pressure
©
2002 General Motors Corporation
All Rights Reserved
7-81
77. A common difficulty when diagnosing a problem reported by a
customer is the ______________.
Student Workbook
a. customer’s misconception of results to be expected from the
services to be performed
ASE 1 - Engine
Repair
b. communication of the malfunction from the customer to the service
manager
Module 7 - General
Engine Diagnosis
c. customer’s insistence for the use of nonfactory replacement parts
d. service manager’s inability to quickly recognize the malfunction
78. The engine vacuum reading is low but steady. Which of the following is
the most likely cause of this problem?
a. A sticky valve
b. Leaky fuel injectors
c. Retarded timing
d. Fouled spark plugs
79. A technician is measuring engine vacuum. The needle is normal at idle
but fluctuates rapidly as engine speed is increased. This would
indicate ___________________.
a. improper valve timing
b. blown head gasket
c. weak valve spring
d. burned or warped valve
80. When doing a vacuum test on an engine, the needle occasionally
makes a sharp, fast drop. This would be caused by a/an ________.
a. improper valve timing
b. vacuum leak
c. weak valve spring
d. sticking valve
©
2002 General Motors Corporation
All Rights Reserved
7-82
82. Which of the following will assist in determining which cylinders are
misfiring?
a. DTC P0201 - P0208
b. DTC P0301 - P0308
c. DTC P0401 - P0408
d. DTC P0501 - P0508
Student Workbook
ASE 1 - Engine
Repair
Module 7 - General
Engine Diagnosis
83. When cleaning the external battery case terminals, use __________.
a. a solution of water and baking powder
b. clean mineral spirits
c. a solution of water and baking soda
d. clean water
84. When replacing electrical components, _______________.
a. disconnect the battery ground cable
b. disable the ignition system
c. use only insulated wrenches
d. isolate the alternator to prevent damage
85. All of the following will clear DTCs EXCEPT _____________.
a. disconnect the battery
b. Tech 2
c. grounding the Data Link Connector (DLC)
d. 40 consecutive warm-up cycles
©
2002 General Motors Corporation
All Rights Reserved
7-83
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