Engine Controls - Tests W/o Codes - 5.7l (G Series) Chevrolet Chevy Van G3500

INTRODUCTION

Note. Models may use a Powertrain Control Module (PCM) or Vehicle Control Module (VCM). The term PCM will be used in this article to describe all control modules.

Before diagnosing symptoms or intermittent faults, perform basic diagnostic procedures in the BASIC TESTING - 5.7L article and self-diagnostic steps in the TESTS W/CODES - 5.7L article. Use this article to diagnose driveability problems if a current trouble code is not present or if not equipped with a self-diagnostic system.

Symptom checks are intended to direct technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component or system test, or an adjustment specification. Use intermittent test procedures to locate driveability problems not occurring when vehicle is being tested.

Note. For specific testing, see SYSTEM/COMPONENT TESTS article. For specifications, see the ADJUSTMENTS - 5.7L article or SPECIFICATIONS - 5.7L article.

Note. SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).

PRELIMINARY CHECKS

1. Verify the on-vehicle diagnostics are working by performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the «BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
2. Ensure PCM and MIL function properly.
3. Ensure no trouble codes (except intermittent) are stored.
4. Ensure fuel control system operates properly. See the «BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) 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 specific system/component, such as EGR, TCC, etc. See the SYSTEM/COMPONENT TESTS article for test procedures.

SYMPTOMS

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

Note. If PCM displays data but engine fails to start, see NO-START DIAGNOSIS in the BASIC TESTING - 5.7L article.

SYMPTOM DIAGNOSIS

Symptom checks should not be used unless symptom occurs while vehicle is being tested. To reduce diagnostic time, ensure basic diagnostic procedures in the BASIC TESTING - 5.7L and self-diagnostic steps in the TESTS W/CODES - 5.7L 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 die.

Possible Causes & Corrections

1. Check for restricted exhaust system.
2. Check ignition system for bare or shorted wires, incorrect pick-up coil resistance, loose ignition coil connections or moisture in distributor cap (if equipped).
3. Using Spark Tester (J-26792), check for adequate spark output.
4. Check ignition control circuit for short to ground.
5. Remove spark plugs. Check for wet/fouled spark plugs, cracks in porcelain, improper gap, burned electrodes or heavy carbon deposits.
6. Check for shorts by misting plug wires with water.
7. Check fuel pump relay. Connect test light between fuel pump test terminal and ground. Turn ignition on. Test light should illuminate for 2 seconds. If test light does not illuminate, check fuel pump relay. See the SYSTEM/COMPONENT TESTS article. For location of fuel pump test connector, see the SYSTEM/COMPONENT TESTS article.
8. Check for poor fuel quality or water-contaminated fuel.
9. Check for correct fuel pressure at all speeds and engine RPMs.
10. Check for a faulty in-tank fuel pump check valve (if equipped). A faulty check valve allows fuel in lines to drain back to tank after engine is stopped.
11. Check EGR operation.
12. Ensure ECT circuit or sensor resistance is not too high. See the SENSOR RANGE CHARTS article.
13. Ensure TP sensor does not stick or bind. A sticking throttle shaft or binding linkage may cause a high TP sensor voltage (open throttle indication). PCM will not control idle if high voltage is sensed.
14. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore.
15. Ensure correct PROM is installed in vehicle. Check with dealer for latest application information.

Engine starts okay but dies 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.

1. Ensure Torque Converter Clutch (TCC) is not stuck on.
2. Check brakelight switch operation.
3. Check PCV valve for proper operation.
4. Check for plugged or restricted fuel lines.
5. If engine starts but then immediately stalls, open distributor by-pass circuit. If engine now starts and runs okay, replace distributor pick-up coil.
6. Using Spark Tester (J-26792), check for a weak spark from ignition coil.
7. Check Idle Air Control (IAC) system for proper operation.
8. Unplug MAP sensor. PCM substitutes a default value for sensor signal. If stall condition is eliminated, replace MAP sensor.
9. Check EGR system for proper operation.
10. If stall occurs when air conditioner is turned on, check for air conditioner clutch signal to PCM terminal. Voltage at A/C terminal of PCM should be battery voltage when air conditioner compressor clutch is engaged. A high voltage surge due to a shorted compressor clutch diode could cause PCM shutdown.
11. Check for an overcharged A/C system.

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

1. Check for faulty spark plug wires. Check for fouled spark plugs.
2. Check for open in ignition system ground circuit. Ensure initial ignition timing is correct.
3. Ensure fuel pressure is correct in all speed ranges.
4. Check for poor fuel quality or water-contaminated fuel.
5. Ensure TP sensor does not stick or bind. Voltage should increase at a steady rate as throttle is moved toward wide open throttle.
6. Check MAP sensor response and accuracy. See the SYSTEM/COMPONENT TESTS article.
7. Check canister purge system for proper operation.
8. Check EGR valve for proper operation.
9. Ensure correct PROM is installed in PCM. Check dealer for latest application.
10. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.

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

1. Ensure park/neutral switch is properly adjusted.
2. Check TCC for proper operation.
3. Check for restricted exhaust system.
4. Check for kinked or leaking vacuum lines.
5. Ensure initial ignition timing is properly set.
6. Using Spark Tester (J-26792), check for adequate spark output.
7. Remove spark plugs, and check for wet/fouled spark plugs, cracks in porcelain, improper gap, burned electrodes or heavy carbon deposits. Check distributor cap, rotor and spark plug wires.
8. Check ESC system for proper operation.
9. Check in-line fuel filter. Replace if dirty or clogged.
10. Check fuel for water contamination.
11. Ensure fuel system pressure is correct at all engine speeds.
12. If emission test shows excessive CO and HC emissions and vehicle emits odor, check all systems and components which could cause engine to run rich.
13. If emission test shows excessive NOx emissions, check all systems and components which could cause engine to run lean or too hot.
14. Check canister purge system for proper operation.
15. Check for an intermittent EGR system problem.
16. Check Oxygen Sensor (O2S) for lead or RTV sealant contamination. Such contamination causes a false high voltage signal to PCM, which responds by leaning air/fuel ratio.
17. Check PCM grounds. Ensure they are clean, tight and properly located.
18. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.
19. Check A/C for excessive charge.

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

1. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in the «BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
2. Check engine valve timing and compression.
3. Check engine for a worn camshaft.
4. Check TCC system for proper operation.
5. Check transmission shift pattern and downshift operation.
6. Using Spark Tester (J-26792), check for adequate spark output.
7. Ensure correct initial ignition timing.
8. Check ESC system for excessive retard.
9. Check EST system for proper operation.
10. Check air filter and fuel filter. Replace if necessary.
11. Ensure fuel system pressure is correct at all engine speeds.
12. Check for poor fuel quality or water-contaminated fuel.
13. Check injector wires for short to ground at air cleaner.
14. Check for spray from one injector on TBI unit. Malfunction may be present in injector assembly or in signal to injector assembly. Isolate malfunction by switching injector connectors. If problem remains with original injector, injector is defective. If malfunction moves with injector connector, problem is an improper signal in injector circuits.
15. Check PCM grounds. Ensure they are clean, tight and properly located.
16. Ensure EGR valve is not always open.
17. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.
18. Check A/C for proper operation.

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

1. Ensure EGR valve is not stuck open.
2. Check engine for sticking or leaking valves.
3. Check for proper valve timing.
4. Check for engine vacuum leaks. Ensure engine is tuned to specifications.
5. Using Spark Tester (J-26792), check available output voltage of ignition coil.
6. Check for crossfire between spark plugs, distributor cap and spark plug wires.
7. Check for an intermittent ignition system problem.
8. Check for erratic spark timing or distributor reference (RPM) signal.
9. Ensure initial ignition timing is properly set.
10. Check for fuel or water in vacuum hose to MAP sensor. Also check for restricted hose.

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 BASIC TESTING - 5.7L article.

Misfire Isolation

1. Start engine. Disconnect IAC motor. Using insulated pliers, remove one spark plug wire from a spark plug, and ground it against engine.
2. Note engine RPM as wire is grounded. Reconnect spark plug wire. Repeat procedure for all cylinders. Stop engine, and reconnect IAC motor.
3. If engine speed drops equally (within 50 RPM) on all cylinders, refer to «ROUGH, UNSTABLE OR INCORRECT IDLE»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wo-codes-57l-g-series) symptom. If there is no engine RPM drop or no excessive variation on one or more cylinders, check spark or compression on respective cylinder(s).

1. Check for restricted exhaust system. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in the «BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
2. Check for bent push rods, broken valve springs or worn camshaft lobes.
3. Check ignition wires for short or faulty insulation.
4. Check distributor cap (if equipped) for moisture, dust or cracks. Finely mist spark plug wires with water to check for shorts.
5. Using Spark Tester (J-26792), check for adequate spark at spark plugs.
6. Check ignition system for faulty grounds.
7. Ensure EST wiring harness is not routed too close to ignition wiring. EST wiring harness routed too close to ignition wiring may cause induced voltage signals.
8. Check ignition coil connections.
9. Remove spark plugs, and check for incorrect heat range, wear, cracks, wetness, improper gap or heavy deposits.
10. Check for poor quality or contaminated fuel.
11. Check for improper fuel pressure.
12. Ensure EGR valve is not stuck open.
13. Check PCM for proper ground circuits.
14. Ensure TP sensor does not stick or bind. TP sensor voltage should be less than 1.25 volts at idle.

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

1. Ensure throttle linkage and/or TP sensor do not stick or bind.
2. Check park/neutral switch circuit. Ensure park/neutral switch is properly adjusted.
3. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in the «BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
4. If rough idle occurs only when engine is hot, check PCV valve for proper operation. Check evaporative emission control system. Check for proper spark plug gap and engine compression.
5. Ensure initial ignition timing is properly set.
6. Disconnect MAP sensor. If condition is corrected, replace sensor.
7. Check engine idle speed (both base and PCM idle).
8. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore.
9. Check EGR system for proper operation.
10. Check power steering pressure switch circuit.

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

1. Problem is most likely in Idle Air Control (IAC) system.
2. Check EGR system.
3. Check park/neutral switch.
4. Disconnect MAP sensor. If condition is corrected, replace sensor.

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

1. Check for a clogged air filter.
2. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in the «BASIC TESTING - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-57l-g-series) article.
3. Check engine compression.
4. Check transmission shift pattern and downshift operation.
5. Check TCC system for proper operation.
6. Check for dragging brakes.
7. Check cooling system thermostat for proper heat range and operation.
8. Ensure initial ignition timing is properly set. Check EST and ESC for proper operation.
9. Remove spark plugs, and check for wet/fouled spark plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
10. Check for fuel pressure too high.
11. Check for fuel pressure regulator leaking into intake manifold.
12. Check ECT sensor for shift in calibration. See COOLANT TEMP RESISTANCE VALUES table in the SENSOR RANGE CHARTS article.
13. Check Oxygen Sensor (O2S) for silicone or lead contamination.
14. Ensure speedometer is properly calibrated.
15. Ensure A/C is not always on.

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

1. Check engine for overheating.
2. Check canister purge system staying on.
3. Check for leaking injectors.
4. Check IAC system.

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

1. Check for low engine coolant and correct coolant solution.
2. Check for obvious overheating problems.
3. Check for loose water pump belt.
4. Check for restricted airflow to radiator or restricted coolant flow.
5. Check for faulty or incorrect thermostat.
6. Check for incorrect basic engine parts such as camshaft, cylinder heads and pistons.
7. Check for plugged PCV system.
8. Check transmission range pressure switch assembly operation.
9. Check transmission shift pattern and downshift operation.
10. Check TCC system for proper operation.
11. Check spark plugs for proper heat range and gap.
12. Check knock sensor system operation.
13. Ensure initial timing is correct.
14. Remove carbon from engine with top engine cleaner.
15. Check for incorrect fuel pressure.
16. Check for poor fuel quality and proper octane rating. If scan tool readings are normal and no engine mechanical faults are present, fill fuel tank with a premium fuel with a minimum octane rating of 92. Re-evaluate vehicle performance.
17. Check for spray from one injector on TBI unit. Malfunction may be present in injector assembly or in signal to injector assembly. Isolate malfunction by switching injector connectors. If problem remains with original injector, injector is defective. If malfunction moves with injector connector, problem is an improper signal in injector circuits.
18. Check for a shifted ECT sensor. See DIAGNOSTICS AIDS in DTC 15 in the «TESTS W/CODES - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series) article.
19. If emission test shows excessive NOx emissions, check all systems and components which could cause engine to run lean or too hot.
20. Check EGR valve for not working.
21. Ensure correct PROM is installed in vehicle. Check dealer for latest application.

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

1. Check for lead contamination of catalytic converter. Check for removal/tampering at restrictor in fuel filler neck.
2. Check for plugged PCV system.
3. Check EGR valve for not working.
4. If emission test shows excessive CO and HC emissions and vehicle emits odor, check all systems and components which could cause engine to run rich.
5. If emission test shows excessive NOx emissions, check all systems and components which could cause engine to run lean or too hot.

INTERMITTENT PROBLEM DIAGNOSIS

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

If problem vehicle does not produce a trouble code, 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.

Intermittent Simulation

Use following methods to reproduce conditions causing intermittent.

1. Apply light vibration to components.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum supply source.

Monitor circuit/component voltage or resistance while attempting to simulate intermittent. If vehicle is running, monitor for trouble codes. Use test results to identify faulty component or circuit.

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

Use following procedures to determine possible causes of intermittent Malfunction Indicator Light (MIL) operation.

1. Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire-to-terminal connections.
2. Check for poor connection from ignition coil to ground or arcing at spark plug wires or plugs.
3. Check wire from Malfunction Indicator Light (MIL) to PCM for short to ground.
4. Check wire from Data Link Connector (DLC) test terminal for intermittent short to ground.
5. Check for poor connections in PCM ground terminals.
6. Check for electrical system interference caused by defective relay, PCM-driven solenoid or switch, which may cause sharp electrical surge. This type of problem will normally occur when faulty component is operated.
7. Check for aftermarket parts which may not have been produced to manufacturers' specifications. Solenoids without original -equipment diodes for circuit protection or voltage regulator using transistors instead of silicone-chip circuitry may cause voltage surges (up to 300 volts) in PCM wiring, causing temporary PCM shutdown. PCM shutdown is a normal response to system overvoltage (over 16 volts on most models). PCM repowers when condition ceases to exist. A rapid shutdown and repower could cause a flickering Malfunction Indicator Light (MIL) with no codes set in memory.
8. Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
9. Ensure EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Ensure ground wire from PCM to distributor or ignition module is connected to a good ground.
10. Check for intermittent short to ground on terminal "B" (diagnostic enable) of Data Link Connector (DLC) or in Malfunction Indicator Light (MIL) circuit.
11. On vehicles not equipped with a driver information center, use scan tester to check for intermittent wiring problem. See SCAN TESTER USAGE in the «TESTS W/CODES - 5.7L»(/chevrolet/chevy-van-g3500/1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-g-series) article.

See also:
• BASIC TESTING - 5.7L
• TESTS W/CODES - 5.7L
• ADJUSTMENTS - 5.7L
• SPECIFICATIONS - 5.7L
• PRELIMINARY CHECKS
• ROUGH, UNSTABLE OR INCORRECT IDLE