Isuzu Trooper (1998-2002 year). Service manual — part 343
6E–285
ENGINE DRIVEABILITY AND EMISSIONS
Hesitation, Sag, Stumble Symptom
Step
Action
Value(s)
Yes
No
1
DEFINITION:
Momentary lack of response as the accelerator is
pushed down. Can occur at any vehicle speed. Usually
most pronounced when first trying to make the vehicle
move, as from a stop sign. May cause the engine to stall
if severe enough.
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
1. Check the fuel control heated oxygen sensors
(HO2S, B1S1 and B2S1). The fuel control heated
oxygen sensors (HO2S) should respond quickly to
different throttle positions. If they don’t, check them
for silicon or other contaminants from fuel or use of
improper RTV sealant. The sensors may have a
white powdery coating.
Silicon contamination causes a high but false
HO2S signal voltage (rich exhaust indication).
The PCM will then reduce the amount of fuel
delivered to the engine, causing a severe
driveability problem. For more information, refer
to
Powertrain Control Module (PCM) and Sensors.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 5
5
1. Check the fuel pressure. Refer to
Fuel System
Pressure Test.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 6
6
Observe the TP angle display on Tech 2 while slowly
increasing throttle pedal.
Does the TP angle display steadily increase from 0% at
closed throttle to 100% at WOT?
—
Go to
Step 7
Go to
Step 18
7
Monitor the long term fuel trim on Tech 2.
Is the long term fuel trim significantly in the negative
range (rich condition)?
—
Go to
Step 8
Go to
Step 9
8
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
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
6E–286
ENGINE DRIVEABILITY AND EMISSIONS
Hesitation, Sag, Stumble Symptom
(Cont'd)
Step
No
Yes
Value(s)
Action
10
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 11
11
1. Check for a loose ignition coil ground.
Refer to
Electronic Ignition System.
2. If a problem is found, repair as necessary.
Was a problem found?
—
Verify repair
Go to
Step 12
12
1. Check the 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 13
13
1. Remove spark plugs and 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 14
14
1. Check the PCM grounds for clearness, 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 15
15
1. Check the MAF sensor connections.
2. If a problem is found, replace the faulty terminals as
necessary. Refer to
Electrical Diagnosis for wiring
repair procedures.
Was a problem found?
—
Verify repair
Go to
Step 16
16
1. Visually/physically check vacuum hoses for splits,
kinks, and proper 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 17
6E–287
ENGINE DRIVEABILITY AND EMISSIONS
Hesitation, Sag, Stumble Symptom
(Cont'd)
Step
No
Yes
Value(s)
Action
17
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 butter
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
18
Replace the TP sensor.
Is the action complete?
—
Verify repair
—
6E–288
ENGINE DRIVEABILITY AND EMISSIONS
Default Matrix Table
Service Procedure Default Strategy
A referral strategy has been established to assist the
technician with additional information when the cause of
the failure cannot be determined. If no problem is found
after performing diagnostics, then refer to the default
matrix table for further diagnostic information.
Default Matrix Table
Strategy Based Diagnostic Charts
Initial Diagnosis
Default Section(s)
On-Board Diagnostic (OBD) System
Check
Vehicle does not enter diagnostics.
Chassis Electrical
On-Board Diagnostic (OBD) System
Check
Vehicle enters diagnostics and
communicates with Tech 2. MIL is
“ON” in diagnostics. Engine does not
start and run.
Ignition System Check
On-Board Diagnostic (OBD) System
Check
Engine starts and runs, no PCM
codes set. Customer complains of
vibration.
—
On-Board Diagnostic (OBD) System
Check
Engine starts and runs, no PCM
codes set. Customer complains of
harsh or soft shift, poor performance,
delayed or no engagement into drive
or reverse, transmission fluid leak,
transmission noise or vibration, or
improper TCC operation.
Automatic Transmission
PCM Power and Ground Check
On-Board Diagnostic (OBD) System
Check.
Chassis Electrical
PCM Power and Ground Check
On-Board Diagnostic (OBD) System
Check. PCM power and ground
circuits OK. Data link voltage
incorrect.
Chassis Electrical
On-Board Diagnostic (OBD) System
Check
Engine starts and runs, no PCM
codes set. Customer complains of
harsh or soft shift, poor performance,
delayed or no engagement into drive
or reverse, transmission fluid leak,
transmission noise or vibration, or
improper TCC operation.
Automatic Transmission
Symptoms
Initial Diagnosis
Default Section(s)
Intermittents
1. On-board Diagnostic (OBD)
system check.
2. Careful visual/physical
inspections.
Chassis Electrical
Hard Starts
1. OBD system check.
2. Sensors (ECT, MAP, MAF, TP) ;
MAP output chart.
3. Fuel system electrical test, fuel
system diagnosis.
4. Ignition system.
5. IAC system check.
Engine Mechanical, Ignition
System Check, Exhaust System
Diagnosis
Surges and/or Chuggles
1. OBD system check.
2. Heated oxygen sensors.
3. Fuel system diagnosis.
4. Ignition system.
Calibration ID “Broadcast
Code”/Service Bulletins, Ignition
System Check, Generator
Output, Exhaust System
Diagnosis, 4L30-E System Test
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