Engine Control System Troubleshooting - No Codes: Diagnosis Oldsmobile Aurora II

PRELIMINARY INSPECTION

1. Verify on-vehicle diagnostics are working by performing appropriate ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
2. Ensure PCM grounds are clean, tight, and properly located.
3. Check vacuum hoses for splits, kinks, leaks, restrictions and proper connections. Ensure vacuum hoses are correctly routed as shown on vehicle emission control information label.
4. Check for air leaks at all intake manifold sealing surfaces.
5. Check ignition wires for cracking, hardness, proper routing and carbon tracking.
6. Check wiring for proper connections and routing, pinches, burns, cuts or other damage.
7. Ensure PCM and MIL are functioning properly.
8. Ensure there are no DTCs stored, or only intermittent DTCs are present.
9. Ensure fuel control system is operating properly. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
10. Perform fuel system pressure test. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
11. Perform a careful visual inspection of all systems.

After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. Not all items listed under each symptom apply to all models and systems. These procedures will normally recommend testing of a specific system or component, such as EGR, ignition, TCC, etc. See appropriate SYSTEM & COMPONENT TESTING article for test procedures.

Note. If PCM displays data but engine fails to start, see NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.

SYMPTOMS

Before proceeding with any symptom diagnosis, perform all steps under PRELIMINARY INSPECTION .

SYMPTOM DIAGNOSIS

Symptom checks should not be used unless symptom occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS articles were performed before diagnosing a symptom. Symptoms available for diagnosis include

1. «Cuts Out, Misses»(ref-125705-S04660049342001101000000)
2. «Detonation/Spark Knock»(ref-125705-S01691869292001101000000)
3. «Engine Backfires»(ref-125705-S13752157572001101000000)
4. «Engine Dieseling/Run-On»(ref-125705-S28397447282001101000000)
5. «Excessive Exhaust Emissions Or Odors»(ref-125705-S27084543132001101000000)
6. «Hard Start»(ref-125705-S23302911262001101000000)
7. «Hesitation, Sag Or Stumble»(ref-125705-S06996575032001101000000)
8. «Lack Of Power, Sluggish Or Spongy»(ref-125705-S14202282032001101000000)
9. «Poor Fuel Economy»(ref-125705-S25465726422001101000000)
10. «Poor Fuel Fill Quality»(ref-125705-S42057411502001101500000)
11. «Rough, Unstable Or Incorrect Idle, Stalling»(ref-125705-S07537448892001101000000)
12. «Vehicle Surges Or Chuggles»(ref-125705-S03896362612001101000000)

Symptom Definition

Cuts out or misses is a steady pulsation or jerking which follows engine speed and is usually more pronounced as engine load increases. Exhaust may have a steady spitting sound at idle or low speed. Perform a careful visual inspection as described in appropriate BASIC DIAGNOSTIC PROCEDURES article.

A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks which change with amount of acceleration.

Fuel ignites in intake manifold or in exhaust system, making a loud popping noise.

Engine continues to run after ignition is turned off but runs very rough. If engine runs smoothly, check ignition switch and adjustment.

Vehicle fails emission test. Vehicle may also have excessive "rotten egg" smell (hydrogen sulfide) being emitted from tailpipe. Excessive odors DO NOT necessarily indicate exhaust emissions are high.

Engine cranks okay, but does not start for a long time. Engine eventually starts, and may stall immediately or run okay.

Momentary lack of response when accelerator is pushed down. Condition occurs at all vehicle speeds or usually occurs when taking off from a stop. If severe enough, may cause engine to stall.

Engine delivers less power than expected. Little or no increase in speed when accelerator is pushed down.

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Fuel economy is noticeably lower than it was previously on this vehicle.

Problem filling fuel tank.

Overfill tank.

Pre-mature shutoff of fuel dispensing nozzle.

Fuel spitback.

Liquid to EVAP canister.

Liquid leak to ground.

Fuel odor.

Engine runs unevenly at idle. If severe enough, vehicle will shake. Idle may vary in RPM. Either problem may cause stalling. Engine idles at incorrect RPM.

Engine power varies under steady throttle or cruise. Vehicle speeds up and slows down without changing position of accelerator pedal.

PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify fault. These procedures may lead to computer setting a DTC which may help in diagnosis.

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

Use scan tool or DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. When monitoring resistance, ensure ignition switch is in OFF position or negative battery cable is disconnected. A status change on scan tool or DVOM while performing test procedures indicates area of fault.

Intermittent Symptom Definition

Malfunction Indicator Light (MIL) illuminates but does not remain on. A stored DTC may or may not exist.