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Engine Controls - Tests W/o Codes - Gasoline: Diagnosis Chevrolet Pickup C3500

Testing & Diagnostics ~2652 words

Symptom Definition

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

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 (ST-125), check for adequate spark output.
  4. Check ignition control circuit for short to ground.
  5. Remove spark plugs. Check for wet plugs, cracks, 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 not, check fuel pump relay. See RELAYS in «SYSTEM/COMPONENT TESTS - GASOLINE»(ref-19749) article in the ENGINE PERFORMANCE section. For location of fuel pump test connector, see COMPONENT LOCATIONS in appropriate «SYSTEM/COMPONENT TESTS - GASOLINE»(ref-19749) article in the ENGINE PERFORMANCE section.
  8. Check for poor fuel quality or water-contaminated fuel.
  9. Check for correct fuel pressure at all speeds.
  10. Check for a faulty in-tank fuel pump check valve. A faulty check valve allows fuel in lines to drain back to tank after engine is stopped.
  11. Check EGR operation.
  12. Ensure ECT sensor circuit resistance or ECT sensor resistance is not too high. See «SENSOR RANGE CHARTS»(/chevrolet/pickup-c3500/1988-2000/remont/sensor-range-charts/#engine-controls-sensor-operating-range-charts) article or DTC 15 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  13. «TESTS W/CODES - 4.3L»(ref-19732)
  14. «TESTS W/CODES - 5.0L»(ref-19750)
  15. «TESTS W/CODES - 5.7L»(ref-19751)
  16. «TESTS W/CODES - 7.4L»(ref-19752)
  17. 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. TP sensor voltage should be .85 volt with throttle closed.
  18. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore. See DTC 35 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  19. Ensure correct PROM is installed in vehicle. Check with dealer for latest application information.
  20. «TESTS W/CODES - 4.3L»(ref-19732)
  21. «TESTS W/CODES - 5.0L»(ref-19750)
  22. «TESTS W/CODES - 5.7L»(ref-19751)
  23. «TESTS W/CODES - 7.4L»(ref-19752)

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.

Possible Causes & Corrections

  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 (ST-125), 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 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.

Possible Causes & Corrections

  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. Proceed to «SYSTEM/COMPONENT TESTS - GASOLINE»(ref-19749) article in the ENGINE PERFORMANCE section for specific testing procedures.
  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 more 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.

Possible Causes & Corrections

  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 (ST-125), check for adequate spark output.
  7. Remove spark plugs, and check for wet plugs, cracks, 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. See DIAGNOSTIC AIDS in DTC 45 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  13. If emission test shows excessive NOx emissions, check all systems and components which could cause engine to run lean or too hot. See DIAGNOSTIC AIDS in DTC 44 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  14. «TESTS W/CODES - 4.3L»(ref-19732)
  15. «TESTS W/CODES - 5.0L»(ref-19750)
  16. «TESTS W/CODES - 5.7L»(ref-19751)
  17. «TESTS W/CODES - 7.4L»(ref-19752)
  18. Check canister purge system for proper operation.
  19. Check for an intermittent EGR system problem.
  20. 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.
  21. Check PCM grounds. Ensure they are clean, tight and properly located.
  22. Check charging system output. Repair if output is less than 9 volts or more than 16 volts.
  23. Check A/C for excessive charge.

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

Possible Causes & Corrections

  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 «BASIC TESTING - GASOLINE»(ref-19753) article in the ENGINE PERFORMANCE section.
  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 (ST-125), check for adequate spark output.
  7. Ensure initial ignition timing is properly set.
  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 more than 16 volts.
  18. Check A/C for proper operation.

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

Possible Causes & Corrections

  1. Ensure EGR valve is not always 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 (ST-125), 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. On some 5.7L engines, check for faulty air injection diverter valve or check valve.
  11. 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 careful visual inspection as described in BASIC TESTING - GASOLINE article in the ENGINE PERFORMANCE section.

CAUTIONGrounding spark plug wire for extended periods may cause catalytic converter overheating.

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

Possible Causes & Corrections

  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 «BASIC TESTING - GASOLINE»(ref-19753) article in the ENGINE PERFORMANCE section.
  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. See DIAGNOSTIC AIDS in DTC 35 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  9. «TESTS W/CODES - 4.3L»(ref-19732)
  10. «TESTS W/CODES - 5.0L»(ref-19750)
  11. «TESTS W/CODES - 5.7L»(ref-19751)
  12. «TESTS W/CODES - 7.4L»(ref-19752)
  13. Check EGR system for proper operation.
  14. Check power steering pressure switch circuit.

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

Possible Causes & Corrections

  1. Problem is most likely in Idle Air Control (IAC) system. See DIAGNOSTIC AIDS in DTC 35 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  2. «TESTS W/CODES - 4.3L»(ref-19732)
  3. «TESTS W/CODES - 5.0L»(ref-19750)
  4. «TESTS W/CODES - 5.7L»(ref-19751)
  5. «TESTS W/CODES - 7.4L»(ref-19752)
  6. Check EGR system.
  7. Check park/neutral switch.
  8. 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.

Possible Causes & Corrections

  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 «BASIC TESTING - GASOLINE»(ref-19753) article in the ENGINE PERFORMANCE section.
  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 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. Proceed to COOLANT TEMPERATURE RESISTANCE VALUES table in «SENSOR RANGE CHARTS»(/chevrolet/pickup-c3500/1988-2000/remont/sensor-range-charts/#engine-controls-sensor-operating-range-charts) article in the ENGINE PERFORMANCE section.
  13. Check Oxygen Sensor (O2S) for silicone or lead contamination.
  14. Ensure speedometer is properly calibrated.
  15. Ensure A/C is not always on.
  16. On some 5.7L engines, ensure air pump output shifts to catalytic converter.

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

Possible Causes & Corrections

  1. Check engine for overheating.
  2. Check canister purge system staying on.
  3. Check for leaking injectors.
  4. Check IAC system. See DIAGNOSTIC AIDS in DTC 35 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  5. «TESTS W/CODES - 4.3L»(ref-19732)
  6. «TESTS W/CODES - 5.0L»(ref-19750)
  7. «TESTS W/CODES - 5.7L»(ref-19751)
  8. «TESTS W/CODES - 7.4L»(ref-19752)

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

Possible Causes & Corrections

  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 PVC 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 tester 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 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  19. If emission test shows excessive NOx emissions, check all systems and components which could cause engine to run lean or too hot. See DTC 44 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  20. «TESTS W/CODES - 4.3L»(ref-19732)
  21. «TESTS W/CODES - 5.0L»(ref-19750)
  22. «TESTS W/CODES - 5.7L»(ref-19751)
  23. «TESTS W/CODES - 7.4L»(ref-19752)
  24. Check EGR valve for not working.
  25. 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.

Possible Causes & Corrections

  1. Check for lead contamination of catalytic converter. Check for removal/tampering at restrictor in fuel filler neck.
  2. Check for plugged PVC system.
  3. Check EGR valve for not working.
  4. On some 5.7L engines, ensure air is not being diverted to exhaust manifold and is being diverted to catalytic converter during normal engine operation.
  5. 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. See DIAGNOSTIC AIDS in DTC 45 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  6. If emission test shows excessive NOx emissions, check all systems and components which could cause engine to run lean or too hot. See DIAGNOSTIC AIDS in DTC 44 chart in appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section below.
  7. «TESTS W/CODES - 4.3L»(ref-19732)
  8. «TESTS W/CODES - 5.0L»(ref-19750)
  9. «TESTS W/CODES - 5.7L»(ref-19751)
  10. «TESTS W/CODES - 7.4L»(ref-19752)

INTERMITTENT PROBLEM DIAGNOSIS

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

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

When using a voltmeter to pinpoint faults, monitor voltage reading with ignition on or vehicle running. A change in status on voltmeter while performing test procedure indicates area of fault. See TEST PROCEDURES under INTERMITTENTS.

When using an ohmmeter to detect problems in circuit, monitor circuit resistance (ohms) with ignition switch in OFF position or with battery disconnected. A change in ohmmeter reading while performing test procedure indicates area of fault. See TEST PROCEDURES under INTERMITTENTS.

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

See also:
• SENSOR RANGE CHARTS

More articles — Engine Controls - Tests W/o Codes - Gasoline