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EGR SYSTEM - DIESEL
1986 Isuzu Trooper II
1986 Exhaust Emission Systems
ISUZU DIESEL EXHAUST GAS RECIRCULATION
P’UP, Trooper II
DESCRIPTION
Exhaust gas recirculation (EGR) system is used to reduce
oxides of nitrogen (NOx) by recycling some exhaust gas back into the
intake manifold to lower combustion chamber temperatures.
The EGR valve is mounted on intake manifold. EGR system
consists of an EGR valve, vacuum switching valve(s), and connecting
hoses and tubes. An electronic EGR controller monitors throttle
position sensor voltage, engine speed and a thermal vacuum valve to
sense coolant temperature.
OPERATION
EGR VALVE
Vacuum diaphragm chamber of EGR valve is connected to a
vacuum pump through vacuum switching valve(s). Vacuum switching
valve(s) allow vacuum to reach EGR valve when opened by signals from
EGR controller. When vacuum overcomes EGR valve spring force, it
opens EGR valve to allow recirculation.
Fig. 1:
Isuzu Diesel EGR System & Vacuum Diagram
ELECTRONIC EGR CONTROLLER
This unit responds to input signals from the speed sensor,
throttle position switch. Electronic EGR controller will signal
vacuum switching valve(s) to open according to input signals.
The electronic EGR controller will open vacuum switching
valve number 1 when coolant temperature is over 122 F (50 C), engine
is between 1200-2500 RPM and throttle position sensor is less than or
equal to .0007 X 2200 RPM + 4.11 volts.
Vacuum switching valve number 1 will also be open when
coolant temperature is over 122 F (50 C), engine is between 2500-3000
RPM and throttle position sensor voltage is between 3.51-4.32 volts.
Electronic EGR controller will open vacuum switching valves
1 and 2 when coolant temperature is over 122 F (50 C) and throttle
position sensor is between .0007 X 2200 RPM + 3.30 and 4.11 volts.
ENGINE SPEED SENSOR
Engine speed sensor is located on the right side of the fuel
injection pump. It has a magnetic pickup which senses speed of
injection pump gear teeth. Engine speed sensor sends these signals to
EGR controller.
THROTTLE POSITION SENSOR
This sensor is mounted on front upper part of fuel injection
pump. As throttle angle changes, resistance value changes. This
signal is sent to the EGR controller.
THERMAL VACUUM VALVE (P’UP)
Mounted on intake manifold, thermal vacuum valve is
connected between vacuum pump and valve switching valves. Valve opens
when coolant temperature reaches 115-129 F (46-54 C). With valve
closed, EGR system does not operate. As coolant warms, valve opens,
allowing normal EGR operation.
VACUUM REGULATOR VALVE (P’UP)
This component reduces vacuum pump vacuum to 8.8 in. Hg.
When vacuum switching valve number 1 is open, vacuum from the vacuum
regulator valve opens EGR valve half way.
VACUUM SWITCHING VALVE(S)
The vacuum switching valve(s) are opened by signals from the
EGR controller. When open, vacuum is allowed to operate EGR valve.
TESTING
COOLANT THERMO SWITCH
Place thermo switch in water. Raise water temperature.
Connect an ohmmeter and check for continuity above 131 F (50 C). If
not, replace coolant thermo switch.
ELECTRONIC EGR CONTROLLER
1) Using a voltmeter, connect positive lead to the
Light-Green or Light-Green/Black wire at the vacuum switching valve
wiring connector. Connect negative test lead to Black/Yellow wire.
2) Check for 12 volts to vacuum switching valve(s) when
engine speed is less than 3000 RPM. If not, replace EGR controller.
EGR VALVE
1) Detach vacuum hose from EGR valve and connect outside
vacuum source, such as hand pump with gauge. Apply vacuum, EGR valve
should not leak down.
2) While applying vacuum, watch movement of valve stem. At
17.7 in. Hg, stem should move diaphragm to full up position. If valve
does not respond as indicated, replace EGR valve.
THROTTLE POSITION SENSOR
Connect a voltmeter to the Blue/Yellow (positive) and
Blue/Red (negative) color coded terminals without disconnecting the
throttle position sensor. Open throttle lever to within 9/32" (7 mm)
from idle stop screw. Voltmeter should read 3.3-4.4 volts after
starting the engine. If not, replace throttle position sensor.
THERMAL VACUUM VALVE (P’UP)
Remove thermal vacuum valve from engine and place sensing
portion in water, 115-129 F (46-54 C). Blow through hoses connected
to valve. Air should pass through. If not, replace valve.
VACUUM REGULATOR VALVE (P’UP)
Attach a vacuum pump and gauge to port "S". Attach a vacuum
gauge to port "Z". Apply 27.5 in. Hg to the vacuum regulator valve.
Vacuum gauge on port "Z" should read 8.8 in. Hg. If not, replace
vacuum regulator valve.
VACUUM SWITCHING VALVE(S)
The vacuum switching valve(s) may be checked by connecting 12
volts directly to terminals. With 12 volts connected, listen for
plunger operation noise.
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