Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 375

6E–530

6VE1 3.5L 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

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?

—

Verify repair

Go to 

Step 4

4

Was a visual/physical check performed?

—

Go to 

Step 5

Go to 

Visual/

Physical

Check

5

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  6

6

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 7

7

Observe the TP 1, 2 angle display on the Tech 2 while
slowly increasing accelerator pedal depression.

Does the TP angle display steadily increase from 8 

∼

10% at closed throttle to 90 

∼

 92% at WOT?

—

Go to 

Step 8

Go to 

Step 9

8

Monitor 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 9

Go to 

Step 10

9

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 11

6E–531

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Hesitation, Sag, Stumble Symptom

  (Cont'd)

Step

No

Yes

Value(s)

Action

10

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 11

11

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 12

12

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 13

13

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 14

14

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 15

15

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 16

16

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 17

6E–532

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Hesitation, Sag, Stumble Symptom

  (Cont'd)

Step

No

Yes

Value(s)

Action

17

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 18

18

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

6E–533

6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

Bank 1 Restricted Exhaust System Check

 

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to 

Step 2

Go to 

OBD

System

Check

2

1. Remove the Bank 1 HO2S 2.
2. Install the Exhaust Backpressure Tester

(BT-8515-V or equivalent) in place of the Bank 1
HO2S 2.

3. Run the engine at normal operating temperature.
4. Increase the engine speed to 2000 RPM and allow

10 seconds for pressure to build.

5. Observe the exhaust system backpressure reading

on the gauge.

Does the reading exceed the amount in the value
column?

8.62 kPa

(1.25 psi)

Go to 

Step 3

Go to 

Step 4

3

Repair the restriction in the exhaust system after the
catalytic converter.
Possible faults include:

D

Collapsed pipe

D

Heat distress

D

Internal muffler failure

Is the action complete?

—

Verify repair

—

4

1. Install the Bank 1 HO2S 2.
2. Install the Exhaust Backpressure Tester in place of

Bank 1 HO2S 1.

3. Run the engine at normal operating temperature.
4. Increase the engine speed to 2000 RPM and allow

10 seconds for pressure to build.

5. Observe the exhaust system backpressure reading

on the gauge.

Does the reading exceed the amount in the value
column?

8.62 kPa

(1.25 psi)

Go to 

Step 5

No trouble

found.  If a
driveability

symptom

exists, refer
to symptom

charts

5

Repair the restriction in the catalytic converter.

Is the action complete?

—

Verify repair

—

NOTE: DTCs will be set by running the vehicle to normal
operating temperature after a cold start with the O2
sensor disconnected.  After performing these tests, use
the Tech 2 to erase the DTCs that were set by the lack of
O2 sensor activity.