Engine Controls - Tests W/o Codes - Efi Isuzu Impulse II

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in F - EFI BASIC TESTING and G - EFI TESTS W/ CODES articles in the ENGINE PERFORMANCE Section. Use this article to diagnose driveability problems existing when a hard fault code is not present or vehicle is not equipped with a self-diagnostic system.

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component, system test or adjustment.

Use intermittent test procedures to locate driveability problems that DO NOT occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present, but no problem was found during self-diagnostic testing.

Note. For specific testing procedures, see I - EFI SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. For specifications, see C - EFI SPECIFICATIONS or D - EFI ADJUSTMENTS articles in the ENGINE PERFORMANCE Section.

SYMPTOM DIAGNOSIS

Note. If engine cranks, but will not start, see F - EFI BASIC TESTING for trouble shooting procedure.

Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure steps in F - EFI BASIC TESTING and G - EFI TESTS W/ CODES articles in the ENGINE PERFORMANCE Section were performed before diagnosing a symptom. Symptoms available for diagnosis include

1. Difficult To Start
2. Surges
3. Lack of Power
4. Spark Knock/Detonation
5. Hesitation, Sag or Stumble
6. Cuts Out or Misses
7. Poor Fuel Mileage
8. Rough or Unstable Idle
9. Excessive Exhaust Emissions or Odors
10. Backfire
11. Dieseling (Run-On)

DIFFICULT TO START

1. Check for contaminated fuel.
2. Check fuel pressure.
3. Check for faulty Throttle Position Sensor (TPS).
4. Check for faulty coolant temperature sensor.
5. Check for loss of crank signal to ECM.
6. Check EGR system.
7. Check fuel pump relay and circuit.
8. Check for faulty in-tank fuel pump check valve.
9. Check ignition system.
10. Check for faulty IAC operation (3.1L).
11. Check for incorrect EEPROM application (Impulse and Stylus).
12. Check for faulty main (or ECM) relay.

SURGES

1. Check ignition system.
2. Check ECM and ignition grounds.
3. Check for contaminated fuel.
4. Check for restricted fuel filter.
5. Check fuel pressure.
6. Check for injector leakage.
7. Check for intermittent EGR at idle.
8. Check for incorrect charging system voltage.
9. Check for faulty PCV operation.
10. Check for faulty Throttle Position Sensor (TPS).
11. Check O2 sensor for silicone contamination from fuel or improper RTV sealant.
12. Check for faulty MAP sensor.
13. Check for faulty coolant temperature sensor.
14. Use Scan tester to ensure vehicle speed sensor reading matches actual vehicle speed.
15. Check for faulty A/C operation.
16. Check for faulty park/neutral switch.

LACK OF POWER

1. Check ignition system.
2. Check for bad ECM or ignition grounds.
3. Check ignition timing.
4. Check for contaminated fuel.
5. Check fuel pressure.
6. Check for restricted fuel filter.
7. Check EGR System.
8. Check for restricted air filter.
9. Check for faulty Throttle Position Sensor (TPS).
10. Check for faulty MAP sensor.
11. Check O2 sensor for silicone contamination from fuel or improper RTV sealant.
12. Check for faulty coolant temperature sensor.
13. Use Scan tester to ensure vehicle speed sensor reading matches actual vehicle speed.
14. Check A/C system operation.
15. Check charging system voltage.
16. Check power steering operation.
17. Check for faulty automatic transmission/transaxle operation.
18. Check valve timing.
19. Check for improper or worn camshaft.
20. Check engine compression.
21. Check for restricted exhaust system.

SPARK KNOCK/DETONATION

1. Check for engine running hot because of low coolant or other cooling system faults.
2. Check for correct fuel octane rating.
3. Check knock sensor (if equipped) and circuit.
4. Check for correct PROM, EEPROM or MEM-CAL (if equipped).
5. Check spark plugs for correct heat range.
6. Check ignition timing.
7. Check for low fuel pressure.
8. Check EGR system operation.
9. Check automatic transmission/transaxle for correct shift points.
10. Check for carbon build-up in cylinders.

HESITATION, SAG OR STUMBLE

1. Check fuel pressure.
2. Check for contaminated fuel.
3. Check for binding TPS.
4. Check ignition timing.
5. Check MAP sensor (if equipped) operation.
6. Ensure charging system voltage is correct.
7. Ensure ignition system is properly grounded.
8. Check for faulty spark plugs or wires.
9. Check canister purge system.
10. Check EGR system.

CUTS OUT OR MISSES

1. Check ignition system.
2. Check spark plugs.
3. Check secondary ignition wires.
4. Check for restricted fuel filter.
5. Check for faulty injector(s).
6. Check fuel pressure.
7. Check for vacuum leaks.
8. Check engine compression.
9. Check valve timing.
10. Check for damaged or worn pushrods, rocker arms, valve springs and camshaft lobes.
11. Check Throttle Position Sensor (TPS) and circuit.

POOR FUEL MILEAGE

1. Check fuel pressure.
2. Check ignition timing.
3. Check spark plugs.
4. Check for correct tire pressure, vehicle carrying heavy loads or poor driving habits.
5. Check if A/C is on all the time.
6. Check for restricted air filter.
7. Check for restricted exhaust system.
8. Check for proper speedometer calibration.
9. Check compression.
10. Check for dragging brakes.
11. Poor gasoline quality.
12. Cooling system running too hot or cold.

ROUGH OR UNSTABLE IDLE

1. Check fuel pressure.
2. Check ignition timing.
3. Check for leaking fuel injector(s).
4. Check for restricted air filter.
5. Check Throttle Position Sensor (TPS) operation.
6. Check for EGR valve open at idle.
7. Check PCV valve operation.
8. Check O2 sensor for silicone contamination from fuel or improper RTV sealant.
9. Check for fuel in fuel pressure regulator hose, indicating a faulty fuel pressure regulator.
10. Check knock sensor operation (if equipped).
11. Check for correct charging system voltage.
12. Check canister purge system operation.
13. Check Idle Air Control (IAC) system operation (if equipped).
14. Check MAP sensor (if equipped) operation.
15. Check for high A/C pressure due to overcharge or faulty pressure switch.
16. Check power steering pressure switch and circuit operation.
17. Ensure battery cables are clean and tight.
18. Ensure engine compression is correct.

EXCESSIVE EXHAUST EMISSIONS OR ODORS

1. Check fuel pressure.
2. Check ignition timing.
3. Check charcoal canister for fuel saturation.
4. Check PCV system operation.
5. Check for faulty spark plugs.
6. Check for lead contamination of catalytic converter.
7. Check for improperly installed fuel filler cap.
8. Check EGR valve operation.
9. Check cooling system operation.

BACKFIRE

1. Check ignition timing.
2. Check ignition coil output.
3. Check for faulty spark plugs.
4. Check EGR system.
5. Check for crossfire between spark plugs.
6. Check for correct valve timing.

DIESELING (RUN-ON)

1. Check for leaking injectors.
2. Check for vacuum leaks.
3. Check for carbon build-up in cylinders.
4. Check for poor fuel quality.

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to the computer setting a fault code (on some systems) which may help in diagnosis.

If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.

Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.

Intermittent Simulation

To reproduce the conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.

Intermittent Check Engine Light & No Trouble Codes Present (Trooper 2.8L)

1. Check for electrical system interference from faulty relay, ECM-driven solenoid or switch. Faulty components can cause sharp electrical surge when operated.
2. Check for incorrect installation of electrical options (2-way radios, cellular phones, etc.). Ensure HEI/EST ignition wiring is routed away from spark plug wiring. Ensure distributor is properly grounded.
3. Check for ignition secondary circuit shorted to ground. Check for shorts on CHECK ENGINE light circuit. Check for poor ECM grounds.