Isuzu Trooper (1998-2002 year). Manual — part 524
6E–466
6VE1 3.5 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
Was the “Electric Throttle Control (ETC) System
Check” performed?
—
Go to
Step 3
Go to
ETC
System
Check
3
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 14
Go to
Step 4
4
Was a visual/physical check performed?
—
Go to
Step 5
Go to
Visual/
Physical
Check
5
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 6
6
Observe the long term fuel trim on the Tech 2.
Is the long term fuel trim significantly in the negative
range (rich condition)?
—
Go to
Step 7
Go to
Step 8
7
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 10
8
Is the long term fuel trim significantly in the positive
range (lean condition)?
—
Go to
Step 9
Go to
Step 10
9
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 10
10
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 a Tech 2, monitor the Engine Speed.
Is the Engine Speed within the specified values?
Desired Idle
Speed
Go to
Step 12
Go to
Step 11
6E–467
6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Rough, Unstable, or Incorrect Idle, Stalling Symptom
(Cont'd)
Step
No
Yes
Value(s)
Action
11
1. Visually/physically inspect for the following
conditions:
D
Restricted air intake system. Check for a
possible collapsed air intake duct, restricted
air filter element, or foreign objects blocking
the air intake system.
D
Large vacuum leak. Check for a condition that
causes a large vacuum leak, such as an
incorrectly installed or faulty crankcase
ventilation valve or a disconnected brake
booster hose.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 9
12
Check the injector connections. If any of the injectors
are connected to an incorrect cylinder, correct as
necessary.
Was a problem found?
—
Verify repair
Go to
Step 13
13
1. Perform the “Injector Coil/Balance Test” in
Fuel
Metering System.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 14
14
1. Check for fuel in the pressure regulator vacuum
hose.
2. If fuel is present, replace the fuel pressure regulator
assembly. Refer to
Fuel Metering System.
3. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 15
15
1. Check for proper ignition voltage output with spark
tester J 26792 (ST-125). Refer to
Electronic Ignition
System for the procedure.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 16
16
1. Remove spark plugs. Check for wet plugs, cracks,
wear, improper gap, burned electrodes, or heavy
deposits. Refer to
Electronic Ignition System.
NOTE: If spark plugs are gas or oil fouled, the cause of
the fouling must be determined before replacing the
spark plugs.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 17
17
1. Check for a loose ignition coil ground and ION
Sensing Module circuit.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 18
18
1. Check ignition coils for cracks or carbon tracking.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 19
6E–468
6VE1 3.5 ENGINE DRIVEABILITY AND EMISSIONS
Rough, Unstable, or Incorrect Idle, Stalling Symptom
(Cont'd)
Step
No
Yes
Value(s)
Action
19
Using a Tech 2, monitor the throttle position 1 and 2
angle with the engine idling.
Is the TP angle at the specified value and steady?
8
∼
10%
Go to
Step 20
Refer to
DTC
for further
diagnosis
20
1. Check the positive crankcase ventilation (PCV)
valve for proper operation. Refer to
Crankcase
Ventilation System.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 21
21
1. Check the transmission range switch circuit. Use a
Tech 2 and be sure the 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 22
22
1. Check for the following engine mechanical items.
Refer to
Engine Mechanical for diagnosis
procedures:
D
Low compression
D
Sticking or leaking valves
D
Worn camshaft lobe(s)
D
Camshaft drive belt slipped or stripped
D
Incorrect valve timing
D
Worn rocker arms
D
Broken valve springs
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 23
23
1. Check for faulty motor mounts. Refer to
Engine
Mechanical for inspection of mounts.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 24
24
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–469
6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Poor Fuel Economy Symptom
Step
Action
Value(s)
Yes
No
1
DEFINITION:
Fuel economy, as measured by an actual road test, is
noticeably lower than expected. Also, economy is
noticeably lower than it was on this vehicle at one time,
as previously shown by an actual road test.
(Non-standard tires will cause odometer readings to be
incorrect, and that may cause fuel economy to appear
poor when it is actually normal.)
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/
Physical
Check
4
Check owner’s driving habits.
D
Is the A/C “ON” full time (defroster mode “ON”)?
D
Are tires at the correct pressure?
D
Are excessively heavy loads being carried?
D
Is acceleration too much, too often?
Was a problem found?
—
Go to
Step 5
Go to
Step 6
5
Review the items in Step 4 with the customer and
advise as necessary.
Is the action complete?
—
System OK
—
6
1. Visually/physically check: Vacuum hoses for splits,
kinks, and improper connections and routing as
shown on the “Vehicle Emission Control
Information” label.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 7
7
1. Remove and check the air filter element for dirt or for
restrictions. Refer to
Air Intake System.
2. Replace the air filter element if necessary.
Was a repair required?
—
Verify repair
Go to
Step 8
8
1. Remove spark plugs and check for wet plugs,
cracks, wear, improper gap, burned electrodes, or
heavy deposits. Refer to
Spark Plug Replacement.
NOTE: If spark plugs are gas or oil fouled, the cause of
the fouling must be determined before replacing the
spark plugs.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 9
9
1. Check for low engine coolant level. Refer to
Engine
Cooling.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 10
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