1998 ISUZU TROOPER Service Repair Manual

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Page 1209 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±92
ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Diagnosis
StepNo Ye s Value(s) Action
221. Command the fuel pump ªONº with Tech 2.
2. Using suitable pliers which will not damage the f

Page 1210 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±93 ENGINE DRIVEABILITY AND EMISSIONS
Idle Air Control (IAC) System Check
Circuit Description
The powertrain control module (PCM) controls engine
idle speed with the idle air control (IAC) valve.

6E±93 ENGINE DRIVEABILITY AND EMISSIONS
Idle Air Control (IAC) System Check
Circuit Description
The powertrain control module (PCM) controls engine
idle speed with the idle air control (IAC) valve. To increase
idle speed, the PCM retracts the IAC valve pintle away
from its seat, allowing more air to bypass the throttle bore.
To decrease idle speed, it extends the IAC valve pintle
towards its seat, reducing by pass air flow. Tech 2 will
read the PCM commands to the IAC valve in counts.
Higher counts indicate more air bypass (higher idle).
Lower counts indicate less air is allowed to bypass (lower
idle).
Diagnostic Aids
A slow, unstable, or fast idle may be caused by a non-IAC
system problem that cannot be overcome by the IAC
valve. Out of control range IAC Tech 2 counts will be
above 60 if idle is too low, and zero counts if idle is too
high. The following checks should be made to repair a
non-IAC system problem:
Vacuum leak (high idle) ± If idle is too high, stop the
engine. Fully extend (low) IAC with the Tech 2. Start
the engine. If idle speed is above 800 RPM, locate and
correct the vacuum leak, including the PCV system.
Check for binding of the throttle blade or linkage.
Lean heated oxygen sensor signal (high air/fuel ratio) ±
The idle speed may be too high or too low. Engine
speed may vary up and down, and disconnecting the
IAC valve does not help. Diagnostic trouble codes
P0131, P0151, P0171, or P0174 may be set. Tech 2
oxygen (O2) voltage will be less than 100 mV (0.1 V).
Check for low regulated fuel pressure, water in fuel, or
a restricted injector.
Rich heated oxygen sensor signal (low air/fuel ratio) ±
The idle speed will be too low. Tech 2 IAC counts will
usually be above 80. The system is obviously rich and
may exhibit black smoke in the exhaust.
Tech 2 O2 voltage will be fixed at about 750 mV (0.75
V). Check for high fuel pressure, or a leaking or
sticking injector. A silicon-contaminated heated
oxygen sensor will show an O2 voltage slow to
respond on Tech 2.Throttle body ± Remove the IAC valve and inspect the
bore for foreign material.
IAC valve electrical connections ± IAC valve
connections should be carefully checked for proper
contact.
PCV valve ± An incorrect or faulty PCV valve may
result in an incorrect idle speed. Refer to
Diagnosis,
Rough Idle, Stalling.
If intermittent poor driveability or
idle symptoms are resolved by disconnecting the IAC,
carefully recheck the connections and valve terminal
resistance, or replace the IAC.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
1. The Tech 2 is used to extend and retract the IAC
valve. Valve movement is verified by an engine
speed change. If no change in engine speed
occurs, the valve can be resettled when removed
from the throttle body.
2. This step checks the quality of the IAC movement in
step 1. Between 700 revolutions per minute (RPM)
and about 1500 RPM, the engine speed should
change smoothly with each flash of the tester light
in both extend and retract. If the IAC valve is
retracted beyond the control range (about 1500
RPM), it may take many flashes to extend the IAC
valve before engine speed will begin to drop. This
is normal on certain engines. Fully extending the
IAC may cause engine stall. This may be normal.

Page 1211 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±94
ENGINE DRIVEABILITY AND EMISSIONS
Idle Air Control (IAC) System Check
StepActionValue(s)Ye sNo
11. Ignition ªOFF.º
2. Connect the Tech 2.
3. Set the parking brake.
4. Block the wheels.
5. Tu

Page 1212 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±95 ENGINE DRIVEABILITY AND EMISSIONS
Knock Sensor (KS) System Check
(Engine Knock, Poor Performance, or Poor Economy)
D06RW035
Circuit Description
The knock sensor (KS) sends an AC voltage signal

Page 1213 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±96
ENGINE DRIVEABILITY AND EMISSIONS
Knock Sensor (KS) System Check
(Engine Knock, Poor Performance, or Poor Economy)
StepActionValue(s)Ye sNo
1Is DTC P0325 or P0327 set?
Ð
Go to DTC
P0325 or
D

Page 1214 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±97 ENGINE DRIVEABILITY AND EMISSIONS
Exhaust Gas Recirculation (EGR) System Check
D06RW106
Circuit Description
A properly operation exhaust gas recirculation (EGR)
system will directly affect the

Page 1215 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±98
ENGINE DRIVEABILITY AND EMISSIONS
Exhaust Gas Recirculation (EGR) System Check
StepActionValue(s)Ye sNo
1Check the EGR valve for looseness.
Is the EGR valve Loose?
ÐGo to Step 2Go to Step 3
2

Page 1216 of 3573

ISUZU TROOPER 1998 Service Repair Manual 6E±99 ENGINE DRIVEABILITY AND EMISSIONS
Manifold Absolute Pressure (MAP) Output Check
D06RW102
Circuit Description
The manifold absolute pressure (MAP) sensor measures
the changes in the intake MAP w

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