Engine Controls - Tests W/o Codes Geo Storm I

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in BASIC TESTING and 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 an 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 - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. For specifications, see ADJUSTMENTS or SPECIFICATIONS articles in the ENGINE PERFORMANCE Section.

SYMPTOM DIAGNOSIS

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

1. Hard starting (cranks okay)
2. Engine surges
3. Lack of power, sluggish or spongy
4. Detonation/spark knock
5. Hesitation, sag or stumble
6. Cuts out, misses
7. Rough, unstable or incorrect idle
8. Poor fuel economy
9. Excessive exhaust emissions
10. Engine diesels
11. Engine backfires

Note. Systems and components listed under each symptom may not be applicable on all models.

HARD STARTING (CRANKS OKAY)

If vehicle cranks okay, but is difficult to start or starts and immediately dies, check the following items

1. Ensure sufficient secondary spark is available.
2. Ensure distributor pick-up coil resistance is within specification.
3. Ensure distributor pick-up coil air gap is correct.
4. Ensure ignition coil resistance is within specification.
5. Check for low compression.
6. Ensure no vacuum leaks exist.
7. Check fuel pump or circuit opening relay.
8. Check fuel pressure.
9. Check for faulty in-tank fuel pump check valve, allowing fuel from lines to drain back to tank after engine has stopped.
10. Check EGR valve and solenoid operation.
11. Check air intake system for restriction.
12. Check for cracks or poor connections at throttle body.
13. Ensure ignition and valve timing are correct.
14. Check for faulty spark plug wires.
15. Ensure noise suppressor (if equipped) has correct resistance.
16. Check operation of air induction valve (if equipped).
17. Ensure Coolant Temperature Sensor (CTS) has correct resistance.
18. Check Throttle Position Sensor (TPS).
19. Check Manifold Absolute Pressure (MAP) sensor.
20. Ensure all fuses are okay.
21. Ensure Idle Air Control (IAC) valve is operating correctly.

ENGINE SURGES

If engine power varies during steady throttle operation, check the following items

1. Ensure no vacuum leaks exist.
2. Check for proper Torque Converter Clutch (TCC) operation.
3. Check EGR valve and solenoid operation.
4. Check fuel pressure.
5. Check in-line fuel filter and replace if dirty or clogged.
6. Check fuel for water contamination.
7. Check O2 sensor operation and for RTV sealant contamination. This will cause a false high voltage signal to ECM. The ECM will respond by reducing (leaner) air/fuel ratio.
8. Verify ignition timing is correct.
9. Ensure sufficient secondary spark is available.
10. Check ECM ground connections.
11. Check for faulty spark plugs.
12. Check for defective spark plug wires.
13. Check for restricted exhaust.
14. Check charging system output. Repair charging system if voltage is not between 9-16 volts.

LACK OF POWER, SLUGGISH OR SPONGY

If engine delivers less power than expected, or if there is little or no increase in speed when accelerator pedal is depressed, check the following items

1. A/C clutch disengages at full throttle (Metro and Tracker).
2. Check throttle cable adjustment.
3. Verify air intake or exhaust system is not restricted.
4. Check fuel pressure.
5. Check in-line fuel filter and replace if dirty or clogged.
6. Ensure sufficient secondary spark exists.
7. Ensure ignition timing and controls are working properly.
8. Check ECM ground connections.
9. Check EGR valve and solenoid operation.
10. Check charging system output. Repair charging system if voltage is not between 9-16 volts.
11. Check Torque Converter Clutch (TCC) operation.
12. Check for faulty spark plugs.
13. Check for defective spark plug wires.
14. Ensure valve timing and engine compression are okay.
15. Check for worn camshaft.

DETONATION/SPARK KNOCK

If engine exhibits a mild-to-severe ping or knock (usually worse under acceleration), check the following items

1. Ensure ignition timing and controls are working properly.
2. Ensure spark plug application and gap is correct.
3. Check EGR valve and solenoid operation.
4. Ensure transaxle/transmission shift points are correct.
5. Check Torque Converter Clutch (TCC) operation.
6. Ensure correct ECM application. Check with dealer for latest application information.
7. Check for engine overheating.
8. Check coolant temperature sensor.
9. Check for contaminated or poor quality fuel.
10. Check fuel pressure.
11. Check for incorrect or damaged basic engine parts such as camshaft, cylinder heads or pistons.
12. Check for excessive carbon build-up on engine components.
13. Check for excessive oil entering the engine.

HESITATION, SAG OR STUMBLE

If there is a momentary lack of throttle response, which may occur at any speed, or is most severe when moving off from a stop, check the following items

1. Check EGR valve and solenoid operation.
2. Check for fouled spark plugs or defective spark plug wires.
3. Check for defective ignition wiring or connections.
4. Ensure ignition timing and controls are working properly.
5. Check throttle position sensor/switch for sticking or misadjustment.
6. Check Manifold Air Temperature (MAT) sensor operation.
7. Check charging system output. Repair charging system if voltage is not between 9-16 volts.
8. Check fuel pressure.
9. Check fuel for water contamination.
10. Ensure correct ECM application. Check with dealer for latest application information.
11. Check Manifold Absolute Pressure (MAP) sensor operation.
12. Check canister purge operation.
13. Check mass airflow sensor.
14. Ensure engine warms to normal operating temperature.

CUTS OUT, MISSES

If a steady jerking exists as engine load increases and is not normally felt a over 30 MPH, check the following items

1. Check for defective spark plugs, spark plug wires, distributor cap or rotor.
2. Check for defective ignition wiring or connections.
3. Check fuel pressure.
4. Check fuel for water contamination.
5. Ensure fuel injectors driver wiring circuit at each injector is operating.
6. Check valve clearance adjustment.
7. Check for low compression.
8. Ensure valve timing is okay.
9. Check for damaged basic engine parts such as camshaft, valves, pistons etc.
10. Check canister purge operation.

ROUGH, UNSTABLE OR INCORRECT IDLE

If engine runs unevenly at idle, idle speed is incorrect or unstable, check the following items

1. Ensure no vacuum leaks exist.
2. Check ECM ground connections.
3. Ensure base idle adjustment is correct.
4. Verify vacuum hose routing is correct.
5. Check for defective ignition system components.
6. Ensure ignition timing and controls are working properly.
7. Ensure all fuel injectors are operating.
8. Clean fuel injectors.
9. Check for fuel in vacuum hose to fuel pressure regulator.
10. Check for low compression.
11. Check for damaged basic engine parts such as camshaft, valves etc.
12. Check O2 sensor operation or for RTV sealant contamination. This will cause a false high voltage signal to ECM. The ECM will respond by reducing (leaner) air/fuel ratio.
13. Check EGR and solenoid operation.
14. Check air valve, IAC or ISC valve operation.
15. Check MAP sensor operation.
16. Ensure throttle linkage is not binding.
17. Check charging system output. Repair charging system if voltage is not between 9-16 volts.
18. Ensure correct ECM application. Check with dealer for latest application information.
19. Check canister purge and PCV valve operation.
20. Check for A/C signal to ECM when A/C is on.
21. Check park/neutral switch operation.
22. A/C system pressure too high.
23. Check coolant temperature sensor.
24. Check mass airflow sensor.

POOR FUEL ECONOMY

If fuel economy is lower than expected during a road test, or has decreased since previous road tests, check the following items

1. Ensure air intake system is not restricted or leaking.
2. Ensure ignition timing and controls are working properly.
3. Check for faulty spark plugs or spark plug wires.
4. Ensure engine warms to normal operating temperature.
5. Check for low compression.
6. Check for restricted exhaust system.
7. Check Torque Converter Clutch (TCC) operation.
8. Check fuel pressure.
9. Check for proper speedometer calibration.
10. Verify brakes are not dragging.
11. Check for faulty ECM.

EXCESSIVE EXHAUST EMISSIONS

If vehicle fails emission test or has excessive "rotten egg smell", check the following items

1. Check fuel pressure.
2. Check for leaking fuel injector if vehicle is running rich.
3. Check canister purge and PCV valve operation.
4. Check throttle position sensor or switch if vehicle is running rich.
5. Check Manifold Absolute Sensor (MAP) if vehicle is running rich.
6. Check EGR operation.
7. Check for vacuum leaks.
8. Ensure ignition timing and controls are working properly.
9. Check for faulty spark plugs or spark plug wires.
10. Check for exhaust leaks.
11. Ensure engine warms to normal operating temperature.
12. Ensure correct ECM application. Check with dealer for latest application information.
13. Check for lead contaminated catalytic converter (look for removal of fuel filler neck restrictor).
14. Check for defective oxygen sensor.

ENGINE DIESELS

If engine continues to run after ignition is turned off, check the following items

1. Check for leaking fuel injectors.

ENGINE BACKFIRES

If fuel ignites in intake manifold or exhaust system and makes a loud popping noise, check the following items

1. Ensure sufficient secondary spark is available.
2. Ensure ignition timing and controls are working properly.
3. Check for faulty spark plugs, spark plug wires, distributor cap and rotor.
4. Check for proper spark plug wire routing.
5. Check for low compression.
6. Ensure valve timing is correct.
7. Check fuel pressure.
8. Check EGR and solenoid operation.

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 is in ON position, or engine is running. Ensure ignition 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.