Engine Controls - Tests W/o Codes Geo Prizm pre-I

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in BASIC TESTING and TESTS W/CODES articles. 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. For specifications, see ADJUSTMENTS or C - TUNE-UP SPECS articles.

SYMPTOMS

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

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 were performed before diagnosing a symptom. Symptoms available for diagnosis include the following

1. Will Not Start (Cranks Okay)
2. Hard Starting (Cranks Okay)
3. Engine Surges
4. Rough, Unstable Or Incorrect Idle
5. Excessive Fast Idle
6. Engine Stalls
7. Lack of Power, Sluggish or Spongy
8. Hesitation, Sag or Stumble
9. Engine Backfires
10. Poor Fuel Economy
11. Detonation/Spark Knock.

Spark

1. Verify ignition fuse is not blown (Metro).
2. Ensure fuel filter is unrestricted.
3. Ensure fuel system pressure and volume are correct.
4. Verify air intake system is unrestricted.
5. Check for poor quality or contaminated fuel. Check for use of fuel with high alcohol content.
6. Check exhaust system for restriction.

No Spark

1. Ensure secondary ignition system is in good condition.
2. Check pick-up coil air gap.
3. Check ignition coil input voltage.
4. Check ignition coil primary resistance.
5. Check ignition coil secondary resistance.
6. Verify noise suppressor has correct resistance.
7. Verify ignitor has correct resistance.
8. Check ignitor primary leads for open or short circuit.

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. Ensure engine has sufficient compression.
6. Ensure there are no vacuum leaks.
7. Check fuel pump relay.
8. Ensure fuel system pressure is correct.
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 PCV valve for free movement.
11. Ensure EGR valve operation is correct and valve closes completely.
12. Check air intake system for restriction.
13. Check for cracks or poor connections at throttle body (if equipped).
14. Ensure ignition and valve timing is correct.
15. Check for faulty spark plug wire.
16. Ensure noise suppressor (if equipped) has correct resistance.
17. Check operation of air induction valve.
18. Check Manifold Air Temperature (MAT) sensor.
19. Check coolant temperature sensor.
20. Check Positive Temperature Coefficient (PTC) system (Tracker-A/T).
21. Check for low compression.

ENGINE SURGES

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

1. Ensure there are no vacuum leaks.
2. Check operation of thermostatic air cleaner damper door.
3. Check for intermittent open or short to ground in Torque Converter Clutch (TCC).
4. Ensure EGR valve operation is correct and valve closes completely.
5. Ensure fuel system pressure is correct and consistent.
6. Check in-line fuel filter and replace if dirty or clogged.
7. Check fuel for water contamination.
8. Check O2 sensor for lead or RTV sealant contamination. This will cause a high false voltage signal to ECM. ECM will respond by reducing (leaner) air/fuel ratio.
9. Verify ignition timing is correct.
10. Check for loose or faulty spark plug.
11. Check A/C for excessive charge.
12. Check spark plug wire for proper resistance, cracked boot or damage to cable.
13. Check ignition timing spark advance system.
14. Check for restricted exhaust.

ROUGH, UNSTABLE OR INCORRECT IDLE

Engine may stall or vehicle may shake, if engine idle speed is incorrect, varies or is uneven. Check the following items

1. Ensure base idle adjustment is correct.
2. Use stethoscope to verify operational noise coming from fuel injector(s).
3. Use Spark Tester (ST-125) to ensure sufficient secondary spark is available.
4. Check air intake system for restrictions.
5. Ensure there are no vacuum leaks.
6. Ensure fuel system pressure and volume are correct.
7. Verify vacuum hose routing is correct.
8. Check for EGR system malfunction.
9. Check air valve or ISC valve for malfunction.
10. Check power steering pressure switch circuit.
11. Check operation of coolant temperature sensor.
12. Check electrical connections at throttle body.
13. Check for cracks or poor connections at airflow meter or throttle body.
14. Check O2 sensor for fluctuating voltage output (0-1.0 volt) with engine at 2000 RPM.
15. Verify throttle position sensor has correct adjustment and resistance value.
16. Ensure throttle linkage and/or TPS are not sticking or binding.
17. If rough idle occurs only when engine is hot, check PCV valve, evaporative emission control system, spark plug gap and compression.

EXCESSIVE FAST IDLE

Check the following items

1. Check coolant temperature sensor operation.
2. Check throttle cable adjustment.
3. Ensure there are no vacuum leaks.
4. Ensure fuel system pressure and volume are correct.
5. Verify vacuum hose routing is correct.
6. Check ISC valve operation (Tracker).
7. Check fuel pressure regulator.

ENGINE STALLS

Engine starts but dies after brief idle. Engine runs only if accelerator is held at part throttle. Engine dies as soon as any load is placed on engine (turning on A/C or engaging transmission). If any of the above conditions applies, check the following items

1. Ensure air intake system is unrestricted.
2. Check PCV system.
3. Check ISC valve for malfunction (Tracker).
4. Check coolant temperature sensor operation.
5. Ensure engine is not overheating.
6. Ensure fuel system pressure is correct. Use ohmmeter to verify correct fuel injector resistance.
7. Check EGR system for correct operation.
8. Check for cracks or poor connections at throttle body.
9. Verify correct throttle position sensor adjustment and resistance value.
10. Disconnect MAF or MAP sensor. If condition is corrected, replace sensor.

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 pushed down, check the following items

1. Ensure air filter and fuel filter are not plugged. Replace if necessary.
2. Check throttle cable adjustment.
3. Verify air intake system is unrestricted.
4. Ensure correct EGR valve and solenoid operations.
5. Ensure fuel system pressure is correct. Use ohmmeter to verify correct fuel injector resistance.
6. Check purge control valve operation.
7. Check vacuum switching valve operation.
8. Check MAP or pressure sensor output.
9. Check throttle position sensor operation.
10. Check coolant temperature sensor operation.
11. Check for proper operation of TCC.
12. Check exhaust system for restriction.
13. Check engine valve timing and compression.

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 air cleaner assembly (clogged filter, restricted air inlet tube, etc.).
2. Check EGR valve and solenoid for correct operation.
3. Check for fouled spark plugs.
4. Ensure ECM controlled idle speed is correct.
5. Check distributor primary terminals for wear or corrosion.
6. Check fuel injector(s) wire harness connector.
7. Check throttle position sensor/switch for sticking or misadjustment.
8. Check Manifold Air Temperature (MAT) sensor operation.
9. Check coolant temperature sensor operation.
10. Check pressure sensor operation.
11. Ensure fuel system pressure is correct at all ranges.
12. Check charging system output. Repair charging system if voltage is not between 9-16 volts.
13. Use ohmmeter to verify correct fuel injector resistance.
14. Check canister purge system for proper operation.
15. Check initial ignition timing and spark advance system.
16. Check for faulty ECM.

ENGINE BACKFIRES

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

1. Ensure exhaust system is not leaking.
2. Check base timing and ensure timing advance system is functional.
3. Using Spark Tester (ST-125), check output of ignition coils.
4. Check for intake manifold gasket leak and TBI gasket-to-manifold leak.
5. Check for proper valve timing.
6. Check engine for sticking or leaky valves.
7. Check ECM and ignition system for faulty grounds.
8. Check throttle body dashpot adjustment (if equipped).
9. Check throttle position sensor.
10. Check coolant temperature sensor.
11. Check air valve, ISC solenoid and idle switch operation.
12. Check intake air system and throttle body electrical connections.
13. Ensure fuel system pressure is correct.
14. Check A/C vacuum solenoid valve (if equipped).

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 idle speed is correct.
2. Ensure air intake system is unrestricted.
3. Ensure fuel system pressure is correct. Use ohmmeter to verify correct fuel injector resistance.
4. Check canister purge control valve operation.
5. Ensure engine has sufficient compression.
6. Ensure correct throttle position sensor or throttle switch adjustment and resistance value.
7. Check operation of coolant temperature sensor.
8. Check for excessive timing retard due to high level of carbon build-up.
9. Check EGR valve and solenoid for correct operation.
10. Check for poor quality or contaminated fuel. Check for fuel with high alcohol content.
11. Ensure spark plug application is correct.
12. Ensure exhaust system is unrestricted.
13. Check MAT sensor signal.
14. Verify brakes are not dragging.
15. Check for faulty ECM.

DETONATION/SPARK KNOCK

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

1. Verify base timing is correct.
2. Check for contaminated or poor quality fuel.
3. Check Electronic Spark Advance (ESA) system.
4. Check EGR system operation.
5. Ensure spark plug application and gap is correct.
6. Check engine oil level.
7. Check for obvious engine overheating.
8. Check for correct operation of thermostatic air-cleaner assembly.
9. Check for vacuum leaks.
10. Check air induction for leaks.
11. Check for incorrect basic engine parts such as camshaft, cylinder heads, pistons, or broken balancer or pulley.
12. Ensure PROM application is correct. Check with dealer for latest application information.
13. Use engine cleaner to remove carbon from engine.

INTERMITTENT PROBLEM DIAGNOSIS

Note. If CHECK ENGINE light comes but does not remain on, then a stored code may or may not exist.

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.