Isuzu Trooper (1998-2002 year). Manual — part 339
6E–269
ENGINE DRIVEABILITY AND EMISSIONS
Lack of Power, Sluggish or Spongy Symptom
(Cont'd)
Step
No
Yes
Value(s)
Action
11
1. Check the PCM grounds for the cleanliness,
tightness and proper locations. Refer to the PCM
wiring diagrams in
Electrical Diagnosis.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 12
12
1. Check the exhaust system for possible restriction:
D
Inspect the exhaust system for damaged or
collapsed pipes.
D
Inspect the muffler for heat distress or possible
internal failure.
D
Check for a possible plugged three-way
catalytic converter by checking the exhaust
system back pressure. Refer to
Restricted
Exhaust System Check.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 13
13
1. Check the torque converter clutch (TCC) for proper
operation. Refer to
4L30-E Transmission
Diagnosis.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 14
14
1. Check for an engine mechanical problem. Check
for low compression, incorrect or worn camshaft,
loose timing belt, etc. Refer to
Engine Mechanical.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 15
15
1. Review all diagnostic procedures within this table.
2. If all procedures have been completed and no
malfunctions have been found, review/inspect the
following:
D
Visual/physical inspection
D
Tech 2 data
D
Freeze Frame data/Failure Records buffer
D
All electrical connections within a suspected
circuit and/or system.
3. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Contact
Technical
Assistance
6E–270
ENGINE DRIVEABILITY AND EMISSIONS
Detonation/Spark Knock Symptom
Step
Action
Value(s)
Yes
No
1
DEFINITION:
A mild to severe ping, usually worse under acceleration.
The engine makes sharp metallic knocks that change
with throttle opening.
Was the “On-Board Diagnostic (OBD) System Check”
performed?
—
Go to
Step 2
Go to
OBD
System
Check
2
1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is found,
correct the condition as instructed in the bulletin.
Was a bulletin found that addresses the symptom?
—
Verify repair
Go to
Step 3
3
Was a visual/physical check performed?
—
Go to
Step 4
Go to
Visual/Physic
al Check
4
If Tech 2 readings are normal (refer to
Typical Scan
Values) and there are no engine mechanical faults, fill
the fuel tank with a known quality gasoline that has a
minimum octane rating of 87 and re-evaluate the
vehicle performance.
Is detonation present?
—
Go to
Step 5
Verify repair
5
1. Check the transmission range switch circuit. Use
Tech 2 and be sure Tech 2 indicates that the vehicle
is in drive with the gear selector in drive or overdrive.
2. If a problem is found, diagnose and repair the
transmission range switch as necessary (refer to
4L30-E Automatic Transmission Diagnosis).
Was a problem found?
—
Verify repair
Go to
Step 6
6
1. Check TCC operation. Refer to
4L30-E
Transmission Diagnosis.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 7
7
1. Check for obvious overheating problems:
D
Low engine coolant.
D
Restricted air flow to radiator, or restricted
water flow through radiator.
D
Correct coolant solution should be a 50/50 mix
of approved antifreeze/coolant and water.
Refer to
Engine Cooling.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 8
8
1. Check fuel pressure. Refer to Chart Fuel System
Pressure Test.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 9
9
1. Check items that can cause an engine to run lean
(long term fuel trim significantly in the positive
range). For a lean condition, refer to
Diagnostic
Aids in DTC P0171 Diagnostic Support.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 10
6E–271
ENGINE DRIVEABILITY AND EMISSIONS
Detonation/Spark Knock Symptom
(Cont'd)
Step
No
Yes
Value(s)
Action
10
1. Spark plugs for proper heat range. Refer to
General
Information.
2. If incorrect spark plugs are installed, replace spark
plugs as necessary.
Did any spark plugs require replacement?
—
Verify repair
Go to
Step 11
11
1. Remove excessive carbon buildup with a top engine
cleaner. Refer to instructions on the top engine
cleaner can.
2. Re-evaluate vehicle performance.
Is detonation still present?
—
Go to
Step 12
Verify repair
12
1. Check for an engine mechanical problem. Perform
a cylinder compression check. Refer to
Engine
Mechanical.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 13
13
1. Review all diagnostic procedures within this table.
2. If all procedures have been completed and no
malfunctions have been found, review/inspect the
following:
D
Visual/physical inspection
D
Tech 2 data
D
Freeze Frame data/Failure Records buffer
D
All electrical connections within a suspected
circuit and/or system.
3. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Contact
Technical
Assistance
6E–272
ENGINE DRIVEABILITY AND EMISSIONS
Rough, Unstable, or Incorrect Idle, Stalling Symptom
Step
Action
Value(s)
Yes
No
1
DEFINITION:
Engine runs unevenly at idle. If severe, the engine or
vehicle may shake. Engine idle speed may vary in
RPM. Either condition may be severe enough to stall
the engine.
Was the “On-Board Diagnostic (OBD) System Check”
performed?
—
Go to
Step 2
Go to
OBD
System
Check
2
1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is found,
correct the condition as instructed in the bulletin.
Was a bulletin found that addresses the symptom?
—
Go to
Step 13
Go to
Step 3
3
Was a visual/physical check performed?
—
Go to
Step 4
Go to
Visual/Physic
al Check
4
1. Check the PCM grounds for cleanliness, tightness
and proper routing. Refer to the PCM wiring
diagrams in
Electrical Diagnosis.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 5
5
Observe the long term fuel trim on Tech 2.
Is the long term fuel trim significantly in the negative
range (rich condition)?
—
Go to
Step 6
Go to
Step 7
6
1. Check items that can cause the engine to run rich.
Refer to
Diagnostic Aids in DTC P0172 Diagnostic
Support.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 9
7
Is the long term fuel trim significantly in the positive
range (lean condition)?
—
Go to
Step 8
Go to
Step 9
8
1. Check items that can cause the engine to run lean.
Refer to
Diagnostic Aids in DTC P0171 Diagnostic
Support.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 9
9
1. Check for incorrect idle speed. Ensure that the
following conditions are present:
D
The engine is fully warm.
D
The accessories are “OFF.”
2. Using Tech 2, monitor the IAC position.
Is the IAC position within the specified values?
Between 10
and 50
counts
Go to
Step 11
Go to
Step 10
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