chapter
chapter
11
DIESEL ENGINE OPERATION
AND DIAGNOSIS
LEARNING OBJECTIVES: After studying this chapter, the reader should be able to: • State the characteristics of
diesel engines. • Describe the fuel tank, lift pump, injection pump, and engine-driven vacuum pump. • Explain the HEUI
system. • Discuss the purpose of glow plugs, diesel fuel heaters, diesel injector nozzles, and accelerator pedal position
sensors. • Explain the purpose of diesel engine turbochargers. • Discuss the purpose of the exhaust gas recirculation system,
selective catalytic reduction, and diesel oxidation catalysts. • Explain diesel particulate matter, and discuss the function of diesel
exhaust particulate filters. • Discuss diesel exhaust smoke diagnosis. • Discuss compression testing, glow plug resistance
balance test, injector pop testing, and diesel emission testing.
KEY TERMS: Diesel exhaust fluid (DEF) 119 • Diesel exhaust particulate filter (DPF) 117 • Diesel oxidation catalyst (DOC) 116
• Differential pressure sensor (DPS) 118 • Direct injection (DI) 107 • Glow plug 112 • Heat of compression 105 • High-pressure common rail (HPCR) 110 • Hydraulic electronic unit injection (HEUI) 110 • Indirect injection (IDI) 107
• Injection pump 105 • Lift pump 108 • Pop tester 122 • Particulate matter (PM) 116 • Opacity 122
• Regeneration 117 • Selective catalytic reduction (SCR) 119 • Soot 116 • Urea 119 • Water-fuel separator 108
Diesel Engines
Fundamentals In 1892, a German engineer named Rudolf
Diesel perfected the compression ignition engine that bears his
name. The diesel engine uses heat created by compression to
ignite the fuel, so it requires no spark ignition system.
The diesel engine requires compression ratios of 16:1
and higher. Incoming air is compressed until its temperature
reaches about 1,000°F (540°C). This is called heat of compression. As the piston reaches the top of its compression
stroke, fuel is injected into the cylinder, where it is ignited by
the hot air. ● See Figure 11–1.
As the fuel burns, it expands and produces power.
Because of the very high compression and torque output of
a diesel engine, it is made heavier and stronger than the same
size gasoline-powered engine.
A diesel engine uses a fuel system with a precision injection
pump and individual fuel injectors. The pump delivers fuel to the
injectors at a high pressure and at timed intervals. Each injector
sprays fuel into the combustion chamber at the precise moment
required for efficient combustion. ● See Figure 11–2.
Advantages and Disadvantages A diesel engine
has several advantages compared to a similar size gasolinepowered engine, including:
1. More torque output
2. Greater fuel economy
3. Long service life
A diesel engine has several disadvantages compared to a
similar size gasoline-powered engine, including:
1. Engine noise, especially when cold and/or at idle speed
2. Exhaust smell
3. Cold weather startability
INJECTOR
EXHAUST
VALVE
AIR
INTAKE
VALVE
FIGURE 11–1 Diesel combustion occurs when fuel is
injected into the hot, highly compressed air in the cylinder.
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TO INJECTORS
HIGH PRESSURE
SENSOR
FUEL RETURN
COMMON RAIL
FUEL FILTER/
WATER
SEPARATOR
FUEL TANK
ECU
INJECTOR
RETURN FUEL
COOLER
HIGH PRESSURE
PUMP
INTAKE LIFT PUMP
FIGURE 11–2 A Typical high-pressure common rail (HPCR) type diesel fuel system.
SYSTEM OR
COMPONENT
DIESEL ENGINE
GASOLINE ENGINE
Block
Cast iron and heavy
(● See Figure
11–3.)
Cast iron or aluminum and as light as
possible
Cylinder head
Cast iron or
aluminum
Cast iron or
aluminum
Compression ratio
17:1–25:1
8:1–12:1
Peak engine speed
2000–2500 RPM
5000–8000 RPM
Pistons
Aluminum with
combustion pockets and heavy-duty
connecting
rods (● See
Figure 11–4.)
Aluminum, usually
flat top or with valve
relief but no
combustion pockets
CHART 11–1
Comparison between a typical gasoline and a diesel engine.
4. Vacuum pump that is needed to supply the vacuum needs
of the heat, ventilation, and air-conditioning system
5. Heavier than a gasoline engine
6. Fuel availability
7. Extra cost compared to a gasoline engine
Construction Diesel engines must be constructed
heavier than gasoline engines because of the tremendous
pressures that are created in the cylinders during operation. ●
SEE CHART 11–1. The torque output of a diesel engine is often
double or more than the same size gasoline-powered engines.
106 FIGURE 11–3 A Cummins diesel engine as found in a Dodge
(Ram) pickup truck. A high-pressure pump (up to 30,000 PSI)
is used to supply diesel fuel to this common rail, which has
tubes running to each injector. Note the thick cylinder walls
and heavy-duty construction.
Air-Fuel Ratios In a diesel engine, air is not controlled
by a throttle as in a gasoline engine. Instead, the amount of fuel
injected is varied to control power and speed. The air-fuel mixture
of a diesel engine can vary from as lean as 85:1 at idle to as rich
as 20:1 at full load. This higher air-fuel ratio and the increased
compression pressures make the diesel more fuel efficient than a
gasoline engine, in part because diesel engines do not suffer from
throttling losses. Throttling losses involve the power needed in a
gasoline engine to draw air past a closed or partially closed throttle.
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PRECHAMBER
FUEL
INJECTOR
INTAKE
VALVE
PISTON
GLOW
PLUG
FIGURE 11–4 A rod/piston assembly from a 5.9 liter
Cummins diesel engine used in a Ram pickup truck.
FIGURE 11–5 An indirect injection diesel engine uses a
prechamber and a glow plug.
In a gasoline engine, the speed and power are controlled by
the throttle valve, which controls the amount of air entering the
engine. Adding more fuel to the cylinders of a gasoline engine
without adding more air (oxygen) will not increase the speed or
power of the engine. In a diesel engine, speed and power are not
controlled by the amount of air entering the cylinders because
the engine air intake is always wide open. Therefore, the engine
always has enough oxygen to burn the fuel in the cylinder and
will increase speed (and power) when additional fuel is supplied.
INTAKE
VALVE
CYLINDER HEAD
PISTON
Note: Many newer diesel engines are equipped with a
throttle valve. This valve is used by the emission control
system and is not designed to control the speed of the
engine.
Indirect and Direct Injection In an indirect
injection (abbreviated IDI) diesel engine, fuel is injected into a
small prechamber, which is connected to the cylinder by a narrow
opening. The initial combustion takes place in this prechamber.
This has the effect of slowing the rate of combustion, which
tends to reduce noise. ● See Figure 11–5.
All indirect injection diesel engines require the use of a
glow plug which is an electrical heater that helps start the combustion process.
In a direct injection (abbreviated DI) diesel engine, fuel
is injected directly into the cylinder. The piston incorporates a
depression where initial combustion takes place. Direct injection diesel engines are generally more efficient than indirect
injection engines, but have a tendency to produce greater
amounts of noise. ● See Figure 11–6.
While some direct injection diesel engines use glow plugs
to help cold starting and to reduce emissions, many direct
injection diesel engines do not use glow plugs.
Diesel Fuel Ignition Ignition occurs in a diesel engine
by injecting fuel into the air charge, which has been heated by
FUEL
INJECTOR
FIGURE 11–6 A direct injection diesel engine injects the fuel
directly into the combustion chamber. Many designs do not
use a glow plug.
compression to a temperature greater than the ignition point of the
fuel or about 1,000°F (538°C). The chemical reaction of burning
the fuel creates heat, which causes the gases to expand, forcing
the piston to rotate the crankshaft. A four-stroke diesel engine
requires two rotations of the crankshaft to complete one cycle.
◼◼
◼◼
◼◼
On the intake stroke, the piston passes top dead center
(TDC), the intake valve(s) opens, and filtered air enters
the cylinder, while the exhaust valve(s) remains open for
a few degrees to allow all of the exhaust gases to escape
from the previous combustion event.
On the compression stroke, after the piston passes BDC,
the intake valve(s) closes and the piston travels up to
TDC (completion of the first crankshaft rotation).
On the power stroke, the piston nears TDC on the
compression stroke and diesel fuel is injected into the
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cylinder by the injectors. The ignition of the fuel does not
start immediately but the heat of compression starts the
combustion phases in the cylinder. During this power
stroke, the piston passes TDC and the expanding gases
force the piston down, rotating the crankshaft.
◼◼
On the exhaust stroke, as the piston passes BDC, the
exhaust valve(s) opens and the exhaust gases start to
flow out of the cylinder. This continues as the piston travels up to TDC, pumping the spent gases out of the cylinder. At TDC, the second crankshaft rotation is complete.
Three Phases
of Combustion
There are three distinct phases or parts to the combustion in a
diesel engine.
1. Ignition delay. Near the end of the compression stroke,
fuel injection begins, but ignition does not begin immediately. This period is called ignition delay.
2. Rapid combustion. This phase of combustion occurs
when the fuel first starts to burn, creating a sudden rise in
cylinder pressure. It is this sudden and rapid rise in combustion chamber pressure that causes the characteristic
diesel engine knock.
3. Controlled combustion. After the rapid combustion
occurs, the rest of the fuel in the combustion chamber
begins to burn and injection continues. This process
occurs in an area near the injector that contains fuel surrounded by air. This fuel burns as it mixes with the air.
Fuel Tank and Lift Pump
Parts Involved A fuel tank used on a vehicle equipped
with a diesel engine differs from the one used with a gasoline
engine in the following ways.
◼◼
◼◼
The filler neck is larger for diesel fuel. The nozzle size
is 15/16 inch (24 mm) instead of 13/16 inch (21 mm) for
gasoline filler necks. Truck stop diesel nozzles for large
over-the-road trucks are usually larger, 1.25 inch or
1.5 inch (32 mm or 38 mm) to allow for faster fueling of
large-capacity fuel tanks.
There are no evaporative emission control devices or a
charcoal (carbon) canister. Diesel fuel is not as volatile
as gasoline and, therefore, diesel vehicles do not have
evaporative emission control devices.
The diesel fuel is usually drawn from the fuel tank by a
separate pump, called a lift pump and delivers the fuel to the
injection pump. Between the fuel tank and the lift pump is a
water-fuel separator. Water is heavier than diesel fuel and
sinks to the bottom of the separator. Part of normal routine
108 FIGURE 11–7 A fuel temperature sensor is being tested
using an ice bath.
maintenance on a vehicle equipped with a diesel engine is to
drain the water from the water-fuel separator. A float is often
used inside the separator, which is connected to a warning
light on the dash that lights if the water reaches a level where
it needs to be drained. The water separator is often part of the
fuel filter assembly. Both the fuel filter and the water separator
are common maintenance items.
Note: Water can cause corrosive damage and wear to
diesel engine parts because it is not a good lubricant.
Water cannot be atomized by a diesel fuel injector nozzle and will often “blow out” the nozzle tip.
Many diesel engines also use a fuel temperature sensor. The computer uses this information to adjust fuel delivery
based on the density of the fuel. ● See Figure 11–7.
Injection Pump
Need for High-Pressure Fuel Pump A diesel
engine injection pump is used to increase the pressure of
the diesel fuel from very low values from the lift pump to the
extremely high pressures needed for injection.
◼◼
◼◼
The lift pump is a low-pressure, high-volume pump.
The high-pressure injection pump is a high-pressure, lowvolume pump.
Injection pumps are usually driven by a gear off the camshaft at the front of the engine. As the injection pump shaft
rotates, the diesel fuel is fed from a fill port to a high-pressure
chamber. If a distributor-type injection pump is used, the fuel
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is forced out of the injection port to the correct injector nozzle
through the high-pressure line. ● See Figure 11–8.
Note: Because of the very tight tolerances in a diesel
engine, the smallest amount of dirt can cause excessive
damage to the engine and to the fuel-injection system.
FUEL
INJECTOR LINES
FUEL
FILTER
FIGURE 11–8 A typical distributor-type diesel injection pump
showing the pump, lines, and fuel filter.
Distributor Injection Pump A distributor diesel
injection pump is a high-pressure pump assembly with lines
leading to each individual injector. The high-pressure lines
between the distributor and the injectors must be the exact
same length to ensure proper injection timing. The highpressure fuel causes the injectors to open. Due to the internal
friction of the lines, there is a slight delay before fuel pressure
opens the injector nozzle. The injection pump itself creates
the injection advance needed for engine speeds above idle
often by using a stepper motor attached to the advance
piston, and the fuel is then discharged into the lines. ● See
Figure 11–9.
FUEL INJECTION PUMP
INJECTION
TIMING
STEPPER
MOTOR
RETURN
LINE
EACH OF THE HIGH
PRESSURE LINES
MUST BE OF
EQUAL LENGTH
PIVOT
ADVANCE
PISTON
FUEL
FILTER
ADVANCE
FUEL
LEVEL
SENSOR
RETARD
LIFT
PUMP
INJECTOR
FUEL TANK
FIGURE 11–9 A schematic of Stanadyne diesel fuel–injection pump assembly showing all of the related components.
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COMMON RAIL
(LEFT BANK)
PRESSURE
LIMITING VALVE
RAIL PRESSURE
COMMON RAIL
SENSOR
(RIGHT BANK)
HIGH PRESSURE PUMP
SENSORS ACTUATORS
FUEL INJECTOR
FILTER
WITH WATER
SEPARATOR
AND INTEGRATED
HAND PUMP
ELECTRONIC
CONTROL
MODULE
TANK
HIGH PRESSURE
LOW PRESSURE
FIGURE 11–10 Overview of a computer-controlled high-pressure common rail V-8 diesel engine.
Note: The lines expand during an injection event. This
is how timing checks are performed. The pulsing of the
injector line is picked up by a probe used to detect the
injection event similar to a timing light used to detect a
spark on a gasoline engine.
electronic unit injection system, or HEUI system. The
components used include:
◼◼
High-pressure engine oil pump and reservoir
◼◼
Pressure regulator for the engine oil
◼◼
High-Pressure Common Rail Newer diesel engines
use a fuel delivery system referred to as a high-pressure
common rail (HPCR) design. Diesel fuel under high pressure,
over 20,000 PSI (138,000 kPa), is applied to the injectors,
which are opened by a solenoid controlled by the computer.
Because the injectors are computer controlled, the combustion
process can be precisely controlled to provide maximum
engine efficiency with the lowest possible noise and exhaust
emissions. ● See Figure 11–10.
Heui System
Principles of Operation Ford 7.3, 6.0, and 6.4
liter (and Navistar) diesels use a system called a hydraulic
110 Passages in the cylinder head for flow of fuel to the
injectors
Operation The engine oil is pressurized to provide an
opening pressure strong enough to overcome the fuel pressure
when the solenoid is commanded to open by the PCM. The
system functions as follows:
◼◼
◼◼
Fuel is drawn from the tank by the tandem fuel pump,
which circulates fuel at low pressure through the fuel
filter/water separator/fuel heater bowl and then fuel is
directed back to the fuel pump where fuel is pumped at
high pressure into the cylinder head fuel galleries.
The injectors, which are hydraulically actuated by engine
oil pressure from the high-pressure oil pump, are then
fired by the powertrain control module (PCM). The control system for the fuel injectors is the PCM, and the
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Tech Tip
Change Oil Regularly in a Ford Diesel Engine
O-RING
GROOVE
Ford 7.3, 6.0, and 6.4 liter diesel engines pump unfiltered oil from the sump to the high-pressure oil pump
and then to the injectors. This means not changing oil
regularly can contribute to accumulation of dirt in the
engine and will subject the fuel injectors to wear and
potential damage as particles suspended in the oil
get forced into the injectors.
◼◼
FIGURE 11–11 A HEUI injector from a Ford PowerStroke
diesel engine. The O-ring grooves indicate the location of the
O-rings that seal the fuel section of the injector from coolant
and from the engine oil.
◼◼
injectors are fired based on sensor inputs received by the
PCM. ● See Figure 11–11.
HEUI injectors rely on O-rings to keep fuel and oil from
mixing or escaping, causing performance problems or engine
damage. HEUI injectors use five O-rings. The three external
O-rings should be replaced with updated O-rings if they fail.
The two internal O-rings are not replaceable and if these fail,
the injector(s) must be replaced. The most common symptoms
of injector O-ring trouble include:
◼◼
Oil getting in the fuel
◼◼
The fuel filter element turning black
◼◼
Long cranking times before starting
◼◼
Sluggish performance
◼◼
Reduction in power
◼◼
◼◼
Injector body. This is the inner part of the nozzle and
contains the injector needle valve and spring, and threads
into the outer heat shield.
Diesel injector needle valve. This precision machined
valve and the tip of the needle seal against the injector
body when it is closed. When the valve is open, diesel
fuel is sprayed into the combustion chamber. This passage is controlled by a computer-controlled solenoid
on diesel engines equipped with computer-controlled
injection.
Injector pressure chamber. The pressure chamber is a
machined cavity in the injector body around the tip of the
injector needle. Injection pump pressure forces fuel into
this chamber, forcing the needle valve open.
Diesel Injector Nozzle Operation The electric
solenoid attached to the injector nozzle is computer controlled
and opens to allow fuel to flow into the injector pressure
chamber. ● See Figure 11–12.
The fuel flows down through a fuel passage in the injector body and into the pressure chamber. The high fuel pressure in the pressure chamber forces the needle valve upward,
Increased oil consumption (This often accompanies
O-ring problems or any fault that lets fuel in the oil.)
Diesel Injector Nozzles
Parts Involved Diesel injector nozzles are springloaded closed valves that spray fuel directly into the combustion
chamber or precombustion chamber when the injector is
opened. Injector nozzles are threaded or clamped into the
cylinder head, one for each cylinder, and are replaceable as an
assembly.
The tip of the injector nozzle has many holes to deliver an
atomized spray of diesel fuel into the cylinder. Parts of a diesel
injector nozzle include:
◼◼
Heat shield. This is the outer shell of the injector nozzle
and may have external threads where it seals in the cylinder head.
FIGURE 11–12 Typical computer-controlled diesel engine
fuel injectors.
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VALVE SPRING
ELECTROMAGNETIC
COIL
PILOT NEEDLE
compressing the needle valve return spring and forcing the
needle valve open. When the needle valve opens, diesel fuel
is discharged into the combustion chamber in a hollow cone
spray pattern.
Any fuel that leaks past the needle valve returns to the fuel
tank through a return passage and line. ● See Figure 11–13.
RETURN SPRING
FUEL
RETURN LINE
BALL
DRAIN ORIFICE
HIGH-PRESSURE
CONNECTION
SERVO-PISTON
NOZZLE SPRING
PRESSURE PIN
NOZZLE NEEDLE
INJECTION
NOZZLE
FIGURE 11–13 A Duramax injector showing all the internal
parts.
Tech Tip
Never Allow a Diesel Engine to Run Out of Fuel
If a gasoline-powered vehicle runs out of gasoline,
it is an inconvenience and a possible additional expense to get some gasoline. However, if a vehicle
equipped with a diesel engine runs out of fuel, it can
be a major concern.
Besides adding diesel fuel to the tank, the other
problem is getting all of the air out of the pump, lines,
and injectors so the engine will operate correctly.
The procedure usually involves cranking the
engine long enough to get liquid diesel fuel back into
the system, but at the same time keeping cranking
time short enough to avoid overheating the starter.
Consult service information for the exact service procedure if the diesel engine is run out of fuel.
Note: Some diesel engines, such as the
General Motors Duramax V-8, are equipped
with a priming pump located under the hood
on top of the fuel filter. Pushing down and
releasing the priming pump with a vent valve
open will purge any trapped air from the system. Always follow the vehicle manufacturer’s
instructions.
112 Glow PLugs
Purpose and Function Glow plugs are always used
in diesel engines equipped with a precombustion chamber and
may be used in direct injection diesel engines to aid starting.
A glow plug is a heating element that uses 12 volts from the
battery and aids in the starting of a cold engine by providing
heat to help the fuel to ignite. ● See Figure 11–14.
As the temperature of the glow plug increases, the resistance of the heating element inside increases, thereby reducing
the current in amperes needed by the glow plugs.
Operation Most glow plugs used in newer vehicles are
controlled by the Powertrain Control Module, which monitors
coolant temperature and intake air temperature. The glow
plugs are turned on or pulsed on or off depending on the
temperature of the engine. The PCM will also keep the glow
plug turned on after the engine starts, to reduce white exhaust
smoke (unburned fuel) and to improve idle quality after starting.
● See Figure 11–15.
The “wait to start” lamp (if equipped) will light when the
engine and the outside temperatures are low to allow time for
the glow plugs to get hot.
FIGURE 11–14 A glow plug assortment showing the various
types and sizes of glow plugs used. Always use the specified
glow plugs.
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GLOW
PLUG
RELAY
CONTROL
ENGINE
CONTROL
MODULE
(ECM)
HOT AT ALL TIMES
BATTERY
FUSE
175 A
3
HOT IN RUN AND START
FUSE
HOLDER
FUEL HEATER
FUSE
15 A
POWER
DISTRIBUTION
FUSIBLE
LINK
FUSE
BLOCK–
UNDERHOOD
FUSIBLE
LINK
3
GLOW
PLUG
RELAY
INTAKE
AIR (IA)
HEATER
RELAY
FUSIBLE
LINK
FUSIBLE
LINK
GLOW
PLUG 2
GLOW
PLUG 4
GLOW
PLUG 6
GLOW
PLUG 8
GLOW
PLUG 1
GLOW
PLUG 3
GLOW
PLUG 5
GLOW
PLUG 7
G101
GLOW
PLUG/INTAKE
HEATER RELAY
ASSEMBLY
52
C1
GLOW
PLUG
SIGNAL
INTAKE
AIR (IA)
HEATER
78
IA HEATER
RELAY
CONTROL
29
C1
INTAKE
HEATER
DIAG 1
62
C2
INTAKE
HEATER
DIAG 2
ENGINE
CONTROL
MODULE
FIGURE 11–15 A schematic of a typical glow plug circuit. Notice that the glow plug relay and intake air heater relay are both
computer controlled.
Heated Inlet Air Some diesel engines, such as the
Ram Cummins and the General Motors 6.6 liter Duramax V-8,
use an electrical heater wire to warm the intake air to help in
cold weather starting and running. ● See Figure 11–16.
Engine-Driven Vacuum Pump
FIGURE 11–16 A wire-wound electric heater is used to warm
the intake air on some diesel engines.
Because a diesel engine is unthrottled, it creates very little vacuum
in the intake manifold. Several engine and vehicle components
operate using vacuum, such as the exhaust gas recirculation
(EGR) valve and the heating and ventilation blend and air doors.
Most diesels used in cars and light trucks are equipped with an
engine-driven vacuum pump to supply the vacuum for these
components.
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?
Frequently Asked Question
How Can You Tell If Gasoline Has Been Added
to the Diesel Fuel by Mistake?
If gasoline has been accidentally added to diesel fuel
and is burned in a diesel engine, the result can be
very damaging to the engine. The gasoline can ignite
faster than diesel fuel, which would tend to increase
the temperature of combustion. This high temperature can harm injectors and glow plugs, as well as
pistons, head gaskets, and other major diesel engine
components. If contaminated fuel is suspected, first
smell the fuel at the filler neck. If the fuel smells like
gasoline, then the tank should be drained and refilled
with diesel fuel. If the smell test does not indicate a
gasoline or any rancid smell, then test a sample for
proper specific gravity.
APP SENSOR
5 V
AP
P#
4 V
2
3 V
APP #
3
2 V
1 V
0
1
P#
AP
25%
50%
75%
100%
PERCENTAGE THROTTLE OPENING
FIGURE 11–17 A typical accelerator pedal position (APP)
sensor uses three different sensors in one package with each
creating a different voltage as the accelerator is moved.
Note: Diesel fuel designed for on-road use
should be green and the price includes a
road use tax. Red diesel fuel should only be
found in off-road or farm equipment and is
not taxed.
Diesel Fuel Heaters
Diesel fuel heaters help prevent power loss and stalling in cold
weather. The heater is placed in the fuel line between the tank
and the primary filter. Some fuel heaters are thermostatically
controlled, which allows fuel to bypass the heater once it has
reached operating temperature.
Accelerator Pedal
Position Sensor
Some light-truck diesel engines are equipped with an electronic throttle to control the amount of fuel injected into the
engine. Because a diesel engine does not use a throttle in the
air intake, the only way to control engine speed is by controlling the amount of fuel being injected into the cylinders. Instead
of a mechanical link from the accelerator pedal to the diesel
injection pump, a throttle-by-wire system uses an accelerator
pedal position (APP) sensor. To ensure safety, it consists of
three separate sensors that change in voltage as the accelerator pedal is depressed. ● See Figure 11–17.
The computer checks for errors by comparing the voltage
output of each of the three sensors inside the APP and compares
them to what they should be if there are no faults. If an error is
detected, the engine and vehicle speed are often reduced.
114 FIGURE 11–18 A Cummins diesel turbocharger is used to
increase the power and torque of the engine.
Diesel Engine
Turbochargers
Turbocharged Diesels A turbocharger greatly
increases engine power by pumping additional compressed air
into the combustion chambers. This allows a greater quantity
of fuel to be burned in the cylinders resulting in greater power
output. In a turbocharger, the turbine wheel spins as exhaust gas
flows out of the engine and drives the turbine blades. The turbine
spins the compressor wheel at the opposite end of the turbine
shaft, pumping air into the intake system. ● See Figure 11–18.
Air Charge Cooler The air charge cooler is installed
in the air flow between the turbocharger discharge and the
inlet air of the engine and is also called an intercooler. It is
needed because the air is heated when compressed by the
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FIGURE 11–19 An air charge cooler is
used to cool the compressed air.
CHARGE
AIR COOLER
AMBIENT
AIR INTAKE
EXHAUST
STROKE
COMPRESSOR
TURBINE
EXHAUST
turbocharger. Cooler air entering the engine means more
power can be produced by the engine. ● See Figure 11–19.
RACK
CAM
Variable Turbocharger A variable turbocharger is
used on many diesel engines for boost control. Boost pressure
is controlled independent of engine speed and a wastegate
is not needed. The adjustable vanes mount to a unison ring
that allows the vanes to move. As the position of the unison
ring rotates, the vanes change angle. The vanes are opened
to minimize flow at the turbine and exhaust back pressure
at low engine speeds. To increase turbine speed, the vanes
are closed. The velocity of the exhaust gases increases, as
does the speed of the turbine. The unison ring is connected
to a cam that is positioned by a rack-and-pinion gear. The
turbocharger’s vane position actuator solenoid connects to a
hydraulic piston, which moves the rack to rotate the pinion gear
and cam. ● See Figure 11–20.
The turbocharger vane position control solenoid valve is
used to advance the unison ring’s relationship to the turbine
and thereby articulate the vanes. This solenoid actuates a
spool valve that applies oil pressure to either side of a piston.
Oil flow has three modes: apply, hold, and release.
◼◼
Apply moves the vanes toward a closed position.
◼◼
Hold maintains the vanes in a fixed position.
◼◼
Release moves the vanes toward the open position.
The turbocharger vane position actuation is controlled by
the ECM, which can change turbine boost efficiency independent of engine speed. The ECM provides a control signal to the
valve solenoid along with a low-side reference. A pulse-widthmodulated signal from the ECM moves the valve to the desired
position.
HYDRAULIC
PISTON
UNISON
RING
TURBINE
ADJUSTABLE
VANES
FIGURE 11–20 A variable vane turbocharger allows the
boost to be controlled without the need of a wastegate.
Exhaust Gas
Recirculation
The EGR system recycles some exhaust gas back into the
intake stream to cool combustion, which reduces oxides of
nitrogen (NOx) emissions. The EGR system includes:
◼◼
◼◼
◼◼
Plumbing that carries some exhaust gas from the turbocharger exhaust inlet to the intake ports
EGR control valve
Stainless steel cooling element used to cool the exhaust
gases ( ● See Figure 11–21.)
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FINE BEACH SAND
(90 µm in. DIAMETER)
HUMAN HAIR
(–70 µm in. DIAMETER)
FIGURE 11–21 A cutaway showing the exhaust cooler. The
cooler the exhaust is, the more effective it is in controlling NOx
emissions.
PM10
(<10 µm in. DIAMETER)
PM2.5
(<2.5 µm in. DIAMETER)
FIGURE 11–22 Relative size of particulate matter to a human
hair.
The EGR valve is PCM controlled and often uses a DC
stepper motor and worm gear to move the valve stem open.
The gear is not attached to the valve and can only force it open.
Return spring force closes the valve. The EGR valve and sensor
assembly is a five-wire design. The PCM uses the position sensor to verify that valve action is as commanded.
?
What Is the Big Deal for the Need to Control
Very Small Soot Particles?
For many years soot or particulate matter (PM) was
thought to be less of a health concern than exhaust
emissions from gasoline engines. It was felt that the
soot could simply fall to the ground without causing
any noticeable harm to people or the environment.
However, it was discovered that the small soot particulates when breathed in are not expelled from the
lungs like larger particles but instead get trapped in
the deep areas of the lungs where they accumulate.
Diesel Particulate
Matter
Particulate Matter Standards Particulate
matter (PM), also called soot, refers to tiny particles of solid or
semisolid material suspended in the atmosphere. This includes
particles between 0.1 and 50 microns in diameter. The heavier
particles, larger than 50 microns, typically tend to settle out
quickly due to gravity. Particulates are generally categorized
as follows:
◼◼
◼◼
◼◼
Total suspended particulate (TSP). Refers to all particles between 0.1 and 50 microns. Up until 1987, the
Environmental Protection Agency (EPA) standard for particulates was based on levels of TSP.
PM10. Refers to particulate matter of 10 microns or less
(approximately 1/6 the diameter of a human hair). EPA
has a standard for particles based on levels of PM10.
PM2.5. Refers to particulate matter of 2.5 microns or less
(approximately 1/20 the diameter of a human hair), also
called “fine” particles. In July 1997, the EPA approved a
standard for PM2.5. ● See Figure 11–22.
Soot Categories In general, soot particles produced
by diesel combustion fall into the following categories.
116 Frequently Asked Question
◼◼
◼◼
Fine. Less than 2.5 microns
Ultrafine. Less than 0.1 micron, and make up 80% to
95% of soot
Diesel Oxidation
Catalyst
Purpose and Function Diesel oxidation catalysts
(DOC) are used in all light-duty diesel engines, since 2007. They
consist of a flow-through honeycomb-style substrate structure
that is wash coated with a layer of catalyst materials, similar
to those used in a gasoline engine catalytic converter. These
materials include the precious metals platinum and palladium,
as well as other base metal catalysts.
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PM
H2O
NO2
CO2
SOOT
BUILDUP
HC
PM
CO
FIGURE 11–23 Chemical reaction within the DOC.
Catalysts chemically react with exhaust gas to convert harmful nitrogen oxide into nitrogen dioxide, and to oxidize absorbed
hydrocarbons. The chemical reaction acts as a combustor for the
unburned fuel that is characteristic of diesel compression ignition. The main function of the DOC is to start a regeneration event
by converting the fuel-rich exhaust gases to heat.
The DOC also reduces:
◼◼
Carbon monoxide (CO)
◼◼
Hydrocarbons (HC)
◼◼
Odor-causing compounds such as aldehydes and sulfur
●
See Figure 11–23.
Diesel Exhaust
Particulate Filter
Purpose and Function Diesel exhaust particulate
filters (DPFs) are used in all light-duty diesel vehicles, since
2007, to meet the exhaust emissions standards. The heated
exhaust gas from the DOC flows into the DPF, which captures
diesel exhaust gas particulates (soot) to prevent them from
being released into the atmosphere. ● See Figure 11–24.
This is done by forcing the exhaust through a porous cell which
DOC
DPF
FIGURE 11–24 Aftertreatment of diesel exhaust is handled
by the DOC and DPF.
FIGURE 11–25 The soot is trapped in the passages of the DPF.
The exhaust has to flow through the sides of the trap and exit.
has a silicon carbide substrate with honeycomb-cell-type
channels that trap the soot. The main difference between the
DPF and a typical catalyst filter is that the entrance to every
other cell channel in the DPF substrate is blocked at one end.
So instead of flowing directly through the channels, the exhaust
gas is forced through the porous walls of the blocked channels
and exits through the adjacent open-ended channels. This type
of filter is also referred to as a “wall-flow” filter.
Operation Soot particulates in the gas remain trapped on
the DPF channel walls where, over time, the trapped particulate
matter will begin to clog the filter. The filter must therefore be
purged periodically to remove accumulated soot particles.
The process of purging soot from the DPF is described as
regeneration. When the temperature of the exhaust gas is
increased, the heat incinerates the soot particles trapped in the
filter and is effectively renewed. ● See Figure 11–25.
Exhaust Gas Temperature Sensors The
following two exhaust gas temperature sensors are used to
help the PCM control the DPF.
◼◼
◼◼
EGT sensor 1 is positioned between the DOC and
the DPF where it can measure the temperature of the
exhaust gas entering the DPF.
EGT sensor 2 measures the temperature of the exhaust
gas stream immediately after it exits the DPF.
The Powertrain Control Module monitors the signals
from the EGT sensors as part of its calibrations to control DPF
regeneration. Proper exhaust gas temperatures at the inlet of
the DPF are crucial for proper operation and for starting the
regeneration process. Too high a temperature at the DPF will
cause the DPF substrate to melt or crack. Regeneration will be
terminated at temperatures above 1,470°F (800°C). With too
low a temperature, self-regeneration will not fully complete the
soot-burning process. ● See Figure 11–26.
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EGT
SENSOR 1
EGT
SENSOR 2
FIGURE 11–26 EGT 1 and EGT 2 are used by the PCM to
help control after treatment system operation.
Dpf Differential Pressure Sensor The DPF
differential pressure sensor (DPS) has two pressure sample
lines.
◼◼
One line is attached before the DPF.
◼◼
The other is located after the DPF.
The exact location of the DPS varies by vehicle model
type such as medium duty, pickup, or van. By measuring the
exhaust supply (upstream) pressure from the DOC, and the
post DPF (downstream) pressure, the PCM can determine
differential pressure, also called “delta” pressure, across the
DPF. Data from the DPF differential pressure sensor is used
by the PCM to calibrate for controlling DPF exhaust system
operation.
Diesel Particulate Filter Regeneration The
primary reason for soot removal is to prevent the buildup of
exhaust back pressure. Excessive back pressure increases fuel
consumption, reduces power output, and can potentially cause
engine damage. Several factors can trigger the diesel PCM to
perform regeneration, including:
CLEANED
AREA
R
E
G
E
N
E
R
A
T
I
O
N
SOOT
CLEANED
AREA
FIGURE 11–27 Regeneration burns the soot and renews the
DPF.
application and operating circumstances. The two main
regeneration types are as follows:
◼◼
◼◼
Passive regeneration. During normal vehicle operation when driving conditions produce sufficient load and
exhaust temperatures, passive DPF regeneration may
occur. This passive regeneration occurs without input
from the PCM or the driver. A passive regeneration may
typically occur while the vehicle is being driven at highway speed or towing a trailer.
Active regeneration. Active regeneration is commanded
by the PCM when it determines that the DPF requires it
to remove excess soot buildup and conditions for filter
regeneration have been met. The vehicle needs to be
◼◼
Distance since last DPF regeneration
?
◼◼
Fuel used since last DPF regeneration
Engine run time since last DPF regeneration
Will the Postinjection Pulses Reduce Fuel
◼◼
◼◼
Exhaust differential pressure across the DPF
DPF Regeneration Process A number of engine
components are required to function together for the
regeneration process to be performed:
1. PCM controls that impact DPF regeneration include late
post-injections, engine speed, and adjusting fuel pressure.
Frequently Asked Question
Economy?
Maybe. Due to the added fuel-injection pulses and
late fuel-injection timing, an increase in fuel consumption may be noticed on the driver information
center (DIC) during the regeneration time period. A
drop in overall fuel economy should not be noticeable. ● See Figure 11–28.
2. Adding late post-injection pulses provides the engine with
additional fuel to be oxidized in the DOC, which increases
exhaust temperatures entering the DPF to 900°F (500°C)
or higher. ● See Figure 11–27.
3. The intake air valve acts as a restrictor that reduces air
entry to the engine, which increases engine operating
temperature.
4. The intake air heater may also be activated to warm intake
air during regeneration.
Types of DPF Regeneration DPF regeneration can
be initiated in a number of ways, depending on the vehicle
118 MAIN
PILOT
PRE
0.4 ms
AFTER
POST
FIGURE 11–28 The post-injection pulse occurs to create the
heat needed for regeneration.
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OUTSIDE AIR
OUTSIDE AIR
FIGURE 11–30 Diesel exhaust fluid is housed in a separate container that holds from 5 to 10 gallons, or enough to last until the
next scheduled oil change in most diesel vehicles that use SCR.
FIGURE 11–29 The exhaust is split into two outlets and has
slits to help draw outside air in as the exhaust leaves the tailpipe. The end result is cooler exhaust gases exiting the tailpipe.
?
Frequently Asked Question
What Is an Exhaust Air Cooler?
An exhaust air cooler is simply a section of tailpipe
that has slits for air to enter. As hot exhaust rushes
past the gap, outside air is drawn into the area which
reduces the exhaust discharge temperature. The
cooler significantly lowers exhaust temperature at the
tailpipe from about 800°F (430°C) to approximately
500°F (270°C). ● See Figure 11–29.
WARNING
Tailpipe outlet exhaust temperature will be greater
than 572°F (300°C) during service regeneration. To
help prevent personal injury or property damage
from fire or burns, keep vehicle exhaust away from
any object and people.
driven at speeds above 30 mph for approximately 20 to
30 minutes to complete a full regeneration. During regeneration, the exhaust gases reach temperatures above
1,000°F (550°C).
Ash Loading Regeneration will not burn off ash. Only the
particulate matter (PM) is burned off during regeneration. Ash is
a noncombustible by-product from normal oil consumption. Ash
accumulation in the DPF will eventually cause a restriction in the
particulate filter. To service an ash-loaded DPF, the DPF will need
to be removed from the vehicle and cleaned or replaced. Low ash
content engine oil (API CJ-4) is required for vehicles with the DPF
system. The CJ-4 rated oil is limited to 1% ash content.
Selective Catalytic
Reduction
Purpose and Function Selective catalytic
reduction (SCR) is a method used to reduce NOx emissions
by injecting urea into the exhaust stream. Instead of using
large amounts of exhaust gas recirculation (EGR), the SCR
system uses a urea. Urea is used as a nitrogen fertilizer. It
is colorless, odorless, and nontoxic. Urea is called diesel
exhaust fluid (DEF) in North America and AdBlue in Europe:
● See Figure 11–30.
The urea is injected into the catalyst where it sets off
a chemical reaction which converts nitrogen oxides (NO x)
into nitrogen (N 2) and water (H 2O). Vehicle manufacturers
size the onboard urea storage tank so that it needs to be
refilled at about each scheduled oil change or every 7,500
miles (12,000 km). A warning light alerts the driver when the
urea level needs to be refilled. If the warning light is ignored
and the diesel exhaust fluid is not refilled, current EPA regulations require that the operation of the engine be restricted
and may not start unless the fluid is refilled. This regulation is
designed to prevent the engine from being operated without
the fluid, which, if not, would greatly increase exhaust emissions. ● See Figure 11–31.
Advantages of Scr Using urea injection instead of
large amounts of EGR results in the following advantages.
◼◼
Potential higher engine power output for the same size
engine
◼◼
Reduced NOx emissions up to 90%
◼◼
Reduced HC and CO emissions up to 50%
◼◼
Reduced particulate matter (PM) by 50%
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OXIDATION
CATALYST
ENGINE
EXHAUST
UREA SCR
NH 3 OXIDE CATALYST
NO X
N2
CO
CO2
HC
H2 O
PM
PM
UREA DOUSING
SYSTEM
FIGURE 11–31 Urea (diesel exhaust fluid) injection is used to reduce NOx exhaust emissions. It is injected after the diesel oxidation catalyst (DOC) and before the diesel particulate filter (DPF) on this 6.7 liter Ford diesel engine.
Disadvantages of Scr Using urea injection instead
of large amounts of EGR results in the following disadvantages.
indication of cylinder misfire on a warm engine. The most
common causes of white exhaust smoke include:
◼◼
Onboard storage tank required for the urea
◼◼
Inoperative glow plugs
◼◼
Difficult to find local sources of urea
◼◼
Low engine compression
Increased costs to the vehicle owner due to having to
refill the urea storage tank
◼◼
Incorrect injector spray pattern
◼◼
Coolant leak into the combustion chamber
◼◼
Diesel Exhaust
Smoke Diagnosis
Although some exhaust smoke is considered normal operation
for many diesel engines, especially older units, the cause of
excessive exhaust smoke should be diagnosed and repaired.
Gray or Blue Smoke Blue exhaust smoke is usually
due to oil consumption caused by worn piston rings, scored
cylinder walls, or defective valve stem seals. Gray or blue
smoke can also be caused by a defective injector(s).
Diesel Performance
Diagnosis
Black Smoke Black exhaust smoke is caused by
incomplete combustion because of a lack of air or a fault in
the injection system that could cause an excessive amount of
fuel in the cylinders. Items that should be checked include the
following:
◼◼
Injector balance test to locate faulty injectors using a
scan tool
Always start the diagnosis of a diesel engine concern by checking the oil. Higher than normal oil level can indicate that diesel
fuel has leaked into the oil. Diesel engines can be diagnosed
using a scan tool in most cases, because most of the pressure
sensors values can be displayed. Common faults include:
◼◼
Hard starting
◼◼
Proper operation of the fuel rail pressure (FRP) sensor
◼◼
No start
◼◼
Restrictions in the intake or turbocharger
◼◼
Extended cranking before starting
◼◼
Engine oil usage
◼◼
Low power
White Smoke White exhaust smoke occurs most often
during cold engine starts because the smoke is usually
condensed fuel droplets. White exhaust smoke is also an
120 Using a scan tool, check the sensor values in ● CHART
11–2. to help pin down the source of the problem. Also check
the minimum pressures that are required to start the engine if a
no-start condition is being diagnosed. ● See Figure 11–32.
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DIESEL TROUBLESHOOTING CHART
5.9 DODGE/RAM CUMMINS 2003–2008
Low-pressure pump
8–12 PSI
Pump amperes
4A
Pump volume
45 oz. in 30 sec.
High-pressure pump
5,000–23,000 PSI
Idle PSI
5,600–5,700 PSI
Electronic Fuel Control (EFC) maximum fuel pressure
Disconnect EFC to achieve maximum pressure
Injector volts
90 V
Injector amperes
20 A
Glow plug amperes
60–80 A × 2 (120–160 A)
Minimum PSI to start
5,000 PSI
GM DURAMAX 2001–2008
Low-pressure pump vacuum
2–10 inch Hg
Pump amperes
NA
Pump volume
NA
High-pressure pump
5,200-5,800 PSI (37–40 MPa)
Idle PSI
5,000–6,000 PSI (30–40 MPa)
Fuel Rail Pressure Regulator (FRPR) maximum fuel pressure
Disconnect to achieve maximum pressure
Injector volts
48 V or 93 V
Injector amperes
20 A
Glow plug amperes
160 A
Minimum to start
1,500 PSI (10 MPa)
SPRINTER 2.7 2002–2006
Low-pressure pump
6–51 PSI
High-pressure pump
800–23,000 PSI
Idle PSI
4,900 PSI
Fuel Rail Pressure Control (FRPC) maximum fuel pressure
Apply power and ground to FRPC to achieve maximum pressure
Injector volts
80 V
Injector amperes
20 A
Glow plug amperes
17 A each (85–95 A total)
Minimum to start
3,200 PSI (1–1.2 V to start)
6.0 POWERSTROKE 2003–2008
Low-pressure pump
50–60 PSI
High-pressure pump
500–4,000 PSI
Idle PSI
500 PSI+
Injection Pressure Regulator (IPR) maximum fuel pressure
Apply power and ground to IPR
Injector volts
48 V
Injector amperes
20 A
Glow plug amperes
20–25 A each (160–200 A total)
Minimum to start
500 PSI (0.85 V)
CHART 11–2
The values can be obtained by using a scan tool and basic test equipment. Always follow the vehicle manufacturer’s recommended procedures.
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Glow Plug Resistance
Balance Test
Glow plugs increase in resistance as their temperature
increases. All glow plugs should have about the same resistance when checked with an ohmmeter. A similar test of the
resistance of the glow plugs can be used to detect a weak cylinder. This test is particularly helpful on a diesel engine that is
not computer controlled. To test for even cylinder balance using
glow plug resistance, perform the following on a warm engine.
1. Unplug, measure, and record the resistance of all glow
plugs.
FIGURE 11–32 A pressure gauge checking the fuel pressure
from the lift pump on a Cummins 6.7 liter diesel.
2. With the wires still removed from the glow plugs, start the
engine.
3. Allow the engine to run for several minutes to allow the
combustion inside the cylinder to warm the glow plugs.
4. Measure the plugs and record the resistance of all glow
plugs.
5. The resistance of all glow plugs should be higher than at
the beginning of the test. A glow plug that is in a cylinder
that is not firing correctly will not increase in resistance as
much as the others.
6. Another test is to measure exhaust manifold temperature
at each exhaust port using an infrared thermometer or a
pyrometer. Misfiring cylinders run cooler than normally
firing cylinders.
Injector Pop Testing
FIGURE 11–33 A compression gauge that is designed for
the higher compression ratio of a diesel engine should be
used when checking the compression.
Compression Testing
A compression test is fundamental for determining the mechanical condition of a diesel engine. To test the compression on a
diesel engine, the following will have to be done.
◼◼
◼◼
Remove the glow plug (if equipped) or the injector.
Use a diesel compression gauge, as the compression is
too high to use a gasoline engine compression gauge.
A diesel engine should produce at least 300 PSI (2,068
kPa) of compression pressure and all cylinders should be
within 50 PSI (345 kPa) of each other. ● See Figure 11–33.
122 A pop tester is a device used for checking a diesel injector nozzle for proper spray pattern. The handle is depressed and popoff pressure is displayed on the gauge. ● See Figure 11–34.
The spray pattern should be a hollow cone, but will vary
depending on design. The nozzle should also be tested for
leakage (dripping of the nozzle) while under pressure. If the
spray pattern is not correct, then cleaning, repairing, or replacing the injector nozzle may be necessary.
Diesel Emission Testing
Opacity Test The most common diesel exhaust emission
test used in state or local testing programs is called the opacity
test. Opacity means the percentage of light that is blocked by
the exhaust smoke.
◼◼
A 0% opacity means that the exhaust has no visible
smoke and does not block light from a beam projected
through the exhaust smoke.
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20% opacity
40% opacity
60% opacity
80% opacity
100% opacity
CHART 11–3
An opacity test is sometimes used during a state emission test
on diesel engines.
◼◼
A 50% opacity means that the exhaust blocks half of the
light from a beam projected through the exhaust smoke.
● SEE CHART 11–3.
Snap Acceleration Test In a snap acceleration test, the
vehicle is held stationary, with wheel chocks in place and brakes
released as the engine is rapidly accelerated to high idle, with the
Tech Tip
FIGURE 11–34 A typical pop tester used to check the spray
pattern of a diesel engine injector.
Tech Tip
Always Use Cardboard to Check for HighPressure Leaks
Do Not Switch Injectors
In the past, it was common practice to switch diesel
fuel injectors from one cylinder to another when diagnosing a dead cylinder problem. However, most highpressure common rail systems used in new diesel engines utilize precisely calibrated injectors that should
not be mixed up during service. Each injector has its
own calibration number. ● See Figure 11–35.
If diesel fuel is found on the engine, a high-pressure
leak could be present. When checking for such
a leak, wear protective clothing including safety
glasses, a face shield, gloves, and a long-sleeved
shirt. Then use a piece of cardboard to locate the
high-pressure leak. When a Duramax diesel is running, the pressure in the common rail and injector
tubes can reach over 20,000 PSI. At these pressures,
the diesel fuel is atomized and cannot be seen but
can penetrate the skin and cause personal injury. A
leak will be shown as a dark area on the cardboard.
When a leak is found, shut off the engine and find the
exact location of the leak without the engine running.
Caution: Sometimes a leak can actually cut
through the cardboard, so use extreme care.
◼◼
A 100% opacity means that the exhaust is so dark that
it completely blocks light from a beam projected through
the exhaust smoke.
FIGURE 11–35 The letters on the side of this injector on a
Cummins 6.7 liter diesel indicate the calibration number for the
injector.
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transmission in neutral while smoke emissions are measured.
This test is conducted a minimum of six times and the three most
consistent measurements are averaged for a final score.
Rolling Acceleration Test Vehicles with a
manual transmission are rapidly accelerated in low gear from
an idle speed to a maximum governed RPM while the smoke
emissions are measured.
Stall Acceleration Test Vehicles with automatic
transmissions are held in a stationary position with the parking
brake and service brakes applied while the transmission is
placed in “drive.” The accelerator is depressed and held
momentarily while smoke emissions are measured.
The standards for diesels vary according to the type of
vehicle and other factors, but usually include a 40% opacity
or less.
Summary
1. A diesel engine uses heat of compression to ignite the diesel fuel when it is injected into the compressed air in the
combustion chamber.
7. Injector nozzles are either opened by the high-pressure
pulse from the distributor pump or electrically by the computer on a common rail design.
2. There are two basic designs of combustion chambers
used in diesel engines. Indirect injection (IDI) uses a precombustion chamber, whereas direct injection (DI) occurs
directly into the combustion chamber.
8. Glow plugs are used to help start a cold diesel engine and
help prevent excessive white smoke during warm-up.
3. The three phases of diesel combustion include:
a. Ignition delay
b. Rapid combustion
c. Controlled combustion
4. The typical diesel engine fuel system consists of the fuel
tank, lift pump, water-fuel separator, and fuel filter.
9. Emissions are controlled on newer diesel engines by using
a diesel oxidation catalytic converter, a diesel exhaust
particulate filter, exhaust gas recirculation, and a selective
catalytic reduction system.
10. Diesel engines can be tested using a scan tool, as well as
measuring the glow plug resistance or compression reading, to determine a weak or nonfunctioning cylinder.
5. The engine-driven injection pump supplies high-pressure
diesel fuel to the injectors.
6. The two most common types of fuel injection used in diesel engines are:
a. Distributor-type injection pump
b.Common rail design where all of the injectors are fed
from the same fuel supply from a rail under high pressure
Review Questions
1. What is the difference between direct injection and indirect injection?
2. What are the three phases of diesel ignition?
3. What are the two most commonly used types of diesel
injection systems?
4. Why are glow plugs kept working after the engine starts?
5. What exhaust after treatment is needed to achieve
exhaust emission standards for vehicles 2007 and newer?
6. What are the advantages and disadvantages of SCR?
Chapter Quiz
1. How is diesel fuel ignited in a warm diesel engine?
a. Glow plugs
b. Heat of compression
c. Spark plugs
d. Distributorless ignition system
2. Which type of diesel injection produces less noise?
a. Indirect injection (IDI)
b. Common rail
c. Direct injection
d. Distributor injection
124 3. Which diesel injection system requires the use of a glow
plug?
a. Indirect injection (IDI)
b. High-pressure common rail
c. Direct injection
d. Distributor injection
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4. The three phases of diesel ignition include ___________.
a. Glow plug ignition, fast burn, slow burn
b. Slow burn, fast burn, slow burn
c. Ignition delay, rapid combustion, controlled
combustion
d. Glow plug ignition, ignition delay, controlled
combustion
5. What fuel system component is used in a vehicle equipped
with a diesel engine that is seldom used on the same vehicle when it is equipped with a gasoline engine?
a. Fuel filter
b. Fuel supply line
c. Fuel return line
d. Water-fuel separator
6. The diesel injection pump is usually driven by a ___________.
a. Gear off the camshaft
b. Belt off the crankshaft
c. Shaft drive off the crankshaft
d. Chain drive off the camshaft
7. Which diesel system supplies high-pressure diesel fuel to
all of the injectors all of the time?
a. Distributor
b. Inline
c. High-pressure common rail
d. Rotary
8. Glow plugs should have high resistance when ___________
and lower resistance when ___________.
a. Cold/warm
b. Warm/cold
c. Wet/dry
d. Dry/wet
9. Technician A says that glow plugs are used to help start a
diesel engine and are shut off as soon as the engine starts.
Technician B says that the glow plugs are turned off as
soon as a flame is detected in the combustion chamber.
Which technician is correct?
a. Technician A only
b. Technician B only
c. Both Technicians A and B
d. Neither Technician A nor B
10. What part should be removed to test cylinder compression on a diesel engine?
a. Injector
b. Intake valve rocker arm and stud
c. Glow plug
d. Glow plug or injector
D I E SE L E N G I N E O PE RAT I O N AN D D IA GN OS IS
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