Engine Controls - Tests W/o Codes: Diagnosis Chevrolet Venture I

PRELIMINARY INSPECTION

1. Verify on-board diagnostics are working by performing appropriate ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
2. Ensure PCM and MIL function properly.
3. Ensure no DTCs (except intermittent) are stored.
4. Ensure fuel control system operates properly. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
5. Perform fuel system pressure test.
6. Visually inspect 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 normally recommend testing of a specific system or component, such as EGR, EST, TCC, etc. See appropriate SYSTEM & COMPONENT TESTING article for test procedures.

SYMPTOMS (GASOLINE)

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

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

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. Hard Start
2. Stalls After Starting
3. Hesitation, Sag Or Stumble
4. Vehicle Surges Or Chuggles
5. Lack Of Power Or Sluggish
6. Engine Backfires
7. Cuts Out, Misses
8. Rough, Unstable Or Incorrect Idle
9. Engine Will Not Idle
10. Poor Fuel Economy
11. Engine Dieseling/Run-On
12. Detonation/Spark Knock
13. Excessive Exhaust Emissions Or Odors

Symptom Definition

Engine cranks okay, but does not start immediately. Engine eventually starts and may run okay or soon stall.

Engine starts okay but stalls after brief idle, as soon as any load is placed on engine (such as turning on air conditioner or engaging transmission) or on initial drive-away.

Momentary lack of response when accelerator is pushed down. May occur at any vehicle speed. Usually occurs after a stop. If severe enough, may cause engine to stall.

Engine power varies under steady throttle or cruise. Feels like vehicle speeds up and slows down even though accelerator pedal position remains constant.

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

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

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

Engine runs unevenly at idle. If bad enough, vehicle will shake. Idle RPM may vary. Engine idles at incorrect RPM.

Engine starts but will not run at idle. Engine runs if accelerator is held at part throttle.

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Current fuel economy is noticeably lower than previous fuel economy.

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

A mild to severe ping, usually worse during acceleration. Engine makes sharp metallic knocks which change with degree of acceleration.

Vehicle fails emission test. Vehicle may also emit "rotten egg" smell (hydrogen sulfide) from exhaust pipe.

SYMPTOMS

To trouble shoot the following symptoms, refer to appropriate number under PROBABLE CAUSES .

1. Engine Lacks Power Check probable causes No. 1, 3, 4, 6-11 and 16-21.
2. Black Smoke Check probable causes No. 2-4, 6-11 and 16-20.
3. Blue Smoke Check probable causes No. 2, 6-8, 13-15 and 17-20.
4. Excessive Oil Consumption Check probable causes No. 2, 6-8, 13-15 and 17-20.
5. Noisy Operation Check probable causes No. 1-8, 11-12 and 19-20.
6. Cyclic Sound From Turbocharger Check probable causes No. 2, 19 and 20.
7. Oil Leak At Turbine Seal Check probable causes No. 13-15 and 17-20.
8. Oil Leak At Compressor Seal Check probable causes No. 2, 8-11, 13-15 and 17-20.

PROBLEM DIAGNOSIS

Intermittent problem diagnosis requires duplication of circuit or component failure in order to identify problem. See TEST PROCEDURES . These procedures may lead to computer recording a DTC which may help diagnosis.

If problem vehicle does not produce a DTC, use a scan tool or DVOM to monitor voltage or resistance values while attempting to reproduce conditions which will create an intermittent problem. A change in status on scan tool or DVOM indicates a problem has been located.

When monitoring voltage, ensure ignition switch is in ON position or engine is running. When monitoring resistance (ohms), 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 problem.

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