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Engine Controls - Tests W/o Codes - Gasoline GMC Suburban I

Testing & Diagnostics ~4187 words

INTRODUCTION

Note. These models may use Electronic Control Modules (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM). PCM will be used in this article to describe all control modules.

Before diagnosing symptoms or intermittent faults, perform steps in appropriate BASIC TESTING and TESTS W/CODES articles below. Use this article to diagnose driveability problems if a hard fault code is not present or if vehicle is not equipped with a self-diagnostic system.

  1. «BASIC TESTING - 2.2L»(ref-20060)
  2. «BASIC TESTING - 3.1L»(ref-20065)
  3. «BASIC TESTING - 3.8L»(ref-20072)
  4. «BASIC TESTING - 4.3L»(ref-20075)
  5. «BASIC TESTING - 5.0L»(ref-20080)
  6. «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l)
  7. «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l)
  8. «TESTS W/CODES - 2.2L»(ref-20062)
  9. «TESTS W/CODES - 3.1L»(ref-20067)
  10. «TESTS W/CODES - 3.8L»(ref-20071)
  11. «TESTS W/CODES - 4.3L»(ref-20077)
  12. «TESTS W/CODES - 5.0L»(ref-20082)
  13. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

Symptom checks are intended to direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to either specific component or system testing or an adjustment specification. Use intermittent test procedures to locate driveability problems which DO NOT occur when the vehicle is being tested.

Note. For specific testing procedures, see appropriate SYSTEM/COMPONENT TESTING article. For specifications, see appropriate ADJUSTMENTS or SPECIFICATIONS article in the ENGINE PERFORMANCE section below.

  1. «SPECIFICATIONS - 2.2L»(ref-20041)
  2. «SPECIFICATIONS - 3.1L»(ref-20043)
  3. «SPECIFICATIONS - 3.8L»(ref-20045)
  4. «SPECIFICATIONS - 4.3L»(ref-20047)
  5. «SPECIFICATIONS - 5.0L»(ref-20049)
  6. «SPECIFICATIONS - 5.7L»(/gmc/suburban/i-1992-1999/remont/specifications/#engine-controls-specifications-57l)
  7. «SPECIFICATIONS - 7.4L»(/gmc/suburban/i-1992-1999/remont/specifications/#engine-controls-specifications-74l)
  8. «ADJUSTMENTS - 2.2L»(ref-20042)
  9. «ADJUSTMENTS - 3.1L»(ref-20044)
  10. «ADJUSTMENTS - 3.8L»(ref-20046)
  11. «ADJUSTMENTS - 4.3L»(ref-20048)
  12. «ADJUSTMENTS - 5.0L»(ref-20050)
  13. «ADJUSTMENTS - 5.7L»(/gmc/suburban/i-1992-1999/remont/adjustments/#engine-controls-adjustments-57l)
  14. «ADJUSTMENTS - 7.4L»(/gmc/suburban/i-1992-1999/remont/adjustments/#engine-controls-adjustments-74l)

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

HOW TO USE THIS SECTION

Use this portion of article only AFTER performing these checks

  1. Ensure on-vehicle diagnostics work (if equipped). Perform DIAGNOSTIC CIRCUIT CHECK in appropriate BASIC TESTING article below.
  2. Ensure PCM and MIL function properly.
  3. Ensure no trouble codes, except intermittent ones, are stored.
  4. «BASIC TESTING - 2.2L»(ref-20060)
  5. «BASIC TESTING - 3.1L»(ref-20065)
  6. «BASIC TESTING - 3.8L»(ref-20072)
  7. «BASIC TESTING - 4.3L»(ref-20075)
  8. «BASIC TESTING - 5.0L»(ref-20080)
  9. «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l)
  10. «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l)
  11. Ensure fuel control system operates properly. Perform FIELD SERVICE MODE CHECK in BASIC TESTING article listed above.
  12. Perform fuel system pressure test.
  13. Visually inspect all systems.

After performing these checks, verify customer complaint, and locate correct symptom from among those listed in this article. Not all items listed under each symptom apply to all models and systems. These procedures normally recommend testing of a system or component on vehicle, such as EGR, EST, TCC, etc. See the appropriate SYSTEM/COMPONENT TESTING article for specific testing procedures.

  1. «SYSTEM/COMPONENT TESTS - 2.2L»(ref-20059)
  2. «SYSTEM/COMPONENT TESTS - 3.1L»(ref-20064)
  3. «SYSTEM/COMPONENT TESTS - 3.8L»(ref-20069)
  4. «SYSTEM/COMPONENT TESTS - 4.3L»(ref-20074)
  5. «SYSTEM/COMPONENT TESTS - 5.0L»(ref-20079)
  6. «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084)
  7. «SYSTEM/COMPONENT TESTS - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-74l) NOTE: If PCM displays data but engine fails to start, see NO-START DIAGNOSIS in appropriate BASIC TESTING article below.
  8. «BASIC TESTING - 2.2L»(ref-20060)
  9. «BASIC TESTING - 3.1L»(ref-20065)
  10. «BASIC TESTING - 3.8L»(ref-20072)
  11. «BASIC TESTING - 4.3L»(ref-20075)
  12. «BASIC TESTING - 5.0L»(ref-20080)
  13. «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l)
  14. «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l)

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/fouled spark 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 test light does not illuminate, check fuel pump relay. See appropriate SYSTEM/COMPONENT TESTING article. For location of fuel pump test connector, see the appropriate SYSTEM/COMPONENT TESTING article below.
  8. «SYSTEM/COMPONENT TESTS - 2.2L»(ref-20059)
  9. «SYSTEM/COMPONENT TESTS - 3.1L»(ref-20064)
  10. «SYSTEM/COMPONENT TESTS - 3.8L»(ref-20069)
  11. «SYSTEM/COMPONENT TESTS - 4.3L»(ref-20074)
  12. «SYSTEM/COMPONENT TESTS - 5.0L»(ref-20079)
  13. «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084)
  14. «SYSTEM/COMPONENT TESTS - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-74l)
  15. Check for poor fuel quality or water-contaminated fuel.
  16. Check for correct fuel pressure at all speeds or engine RPM.
  17. 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.
  18. Check EGR operation.
  19. Ensure ECT sensor circuit resistance or ECT sensor resistance is not too high. See «SENSOR RANGE CHARTS»(/gmc/suburban/i-1992-1999/remont/sensor-range-charts/#engine-controls-sensor-operating-range-charts) article in the ENGINE PERFORMANCE section or DTC 15 chart in appropriate TESTS W/CODES article below.
  20. 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.
  21. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore. See DTC 35 chart in appropriate TESTS W/CODES article below.
  22. «TESTS W/CODES - 2.2L»(ref-20062)
  23. «TESTS W/CODES - 3.1L»(ref-20067)
  24. «TESTS W/CODES - 3.8L»(ref-20071)
  25. «TESTS W/CODES - 4.3L»(ref-20077)
  26. «TESTS W/CODES - 5.0L»(ref-20082)
  27. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)
  28. 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.

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 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.

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. See appropriate SYSTEM/COMPONENT TESTING article for specific testing procedures.
  7. «SYSTEM/COMPONENT TESTS - 2.2L»(ref-20059)
  8. «SYSTEM/COMPONENT TESTS - 3.1L»(ref-20064)
  9. «SYSTEM/COMPONENT TESTS - 3.8L»(ref-20069)
  10. «SYSTEM/COMPONENT TESTS - 4.3L»(ref-20074)
  11. «SYSTEM/COMPONENT TESTS - 5.0L»(ref-20079)
  12. «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084)
  13. «SYSTEM/COMPONENT TESTS - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-74l)
  14. Check canister purge system for proper operation.
  15. Check EGR valve for proper operation.
  16. Ensure correct PROM is installed in PCM. Check dealer for latest application.
  17. 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.

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/fouled spark 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 TESTS W/CODES article 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 TESTS W/CODES article below.
  14. «TESTS W/CODES - 2.2L»(ref-20062)
  15. «TESTS W/CODES - 3.1L»(ref-20067)
  16. «TESTS W/CODES - 3.8L»(ref-20071)
  17. «TESTS W/CODES - 4.3L»(ref-20077)
  18. «TESTS W/CODES - 5.0L»(ref-20082)
  19. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)
  20. Check canister purge system for proper operation.
  21. Check for an intermittent EGR system problem.
  22. 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.
  23. Check PCM grounds. Ensure they are clean, tight and properly located.
  24. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.
  25. 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 appropriate BASIC TESTING article below.
  2. «BASIC TESTING - 2.2L»(ref-20060)
  3. «BASIC TESTING - 3.1L»(ref-20065)
  4. «BASIC TESTING - 3.8L»(ref-20072)
  5. «BASIC TESTING - 4.3L»(ref-20075)
  6. «BASIC TESTING - 5.0L»(ref-20080)
  7. «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l)
  8. «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l)
  9. Check engine valve timing and compression.
  10. Check engine for a worn camshaft.
  11. Check TCC system for proper operation.
  12. Check transmission shift pattern and downshift operation.
  13. Using Spark Tester (ST-125), check for adequate spark output.
  14. Ensure initial ignition timing is properly set.
  15. Check ESC system for excessive retard.
  16. Check EST system for proper operation.
  17. Check air filter and fuel filter. Replace if necessary.
  18. Ensure fuel system pressure is correct at all engine speeds.
  19. Check for poor fuel quality or water-contaminated fuel.
  20. Check injector wires for short to ground at air cleaner.
  21. 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.
  22. Check PCM grounds. Ensure they are clean, tight and properly located.
  23. Ensure EGR valve is not always open.
  24. Check charging system output. Repair if output is less than 9 volts or greater than 16 volts.
  25. 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. 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 appropriate BASIC TESTING article below.

  1. «BASIC TESTING - 2.2L»(ref-20060)
  2. «BASIC TESTING - 3.1L»(ref-20065)
  3. «BASIC TESTING - 3.8L»(ref-20072)
  4. «BASIC TESTING - 4.3L»(ref-20075)
  5. «BASIC TESTING - 5.0L»(ref-20080)
  6. «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l)
  7. «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l)
CAUTIONGrounding spark plug wire for extended periods may cause catalytic converter overheating.

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 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). Possible Causes & Corrections: Check for restricted exhaust system. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in appropriate BASIC TESTING article below. «BASIC TESTING - 2.2L»(ref-20060) «BASIC TESTING - 3.1L»(ref-20065) «BASIC TESTING - 3.8L»(ref-20072) «BASIC TESTING - 4.3L»(ref-20075) «BASIC TESTING - 5.0L»(ref-20080) «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l) «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l) Check for bent push rods, broken valve springs or worn camshaft lobes. Check ignition wires for short or faulty insulation. Check distributor cap (if equipped) for moisture, dust or cracks. Finely mist spark plug wires with water to check for shorts. Connect Spark Tester (ST-125) to spark plug, and check for adequate spark. Check ignition system for faulty grounds. Ensure EST wiring harness is not routed too close to wiring. EST wiring harness routed too close to wiring may cause induced voltage signals. Check ignition coil connections. Remove spark plugs, and check for incorrect heat range, wear, cracks, wetness, improper gap or heavy deposits. Check for proper pick-up coil (HEI distributor) resistance. Check for poor or contaminated fuel. Check for improper fuel pressure. Ensure EGR valve does not stick open. Check PCM for proper ground circuits. 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.

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 appropriate BASIC TESTING article below.
  4. «BASIC TESTING - 2.2L»(ref-20060)
  5. «BASIC TESTING - 3.1L»(ref-20065)
  6. «BASIC TESTING - 3.8L»(ref-20072)
  7. «BASIC TESTING - 4.3L»(ref-20075)
  8. «BASIC TESTING - 5.0L»(ref-20080)
  9. «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l)
  10. «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l)
  11. 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.
  12. Ensure initial ignition timing is properly set.
  13. Disconnect MAP sensor. If condition is corrected, replace sensor.
  14. Check engine idle speed (both base and PCM idle).
  15. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore. See DIAGNOSTIC AIDS in DTC 35 chart in appropriate TESTS W/CODES article below.
  16. «TESTS W/CODES - 2.2L»(ref-20062)
  17. «TESTS W/CODES - 3.1L»(ref-20067)
  18. «TESTS W/CODES - 3.8L»(ref-20071)
  19. «TESTS W/CODES - 4.3L»(ref-20077)
  20. «TESTS W/CODES - 5.0L»(ref-20082)
  21. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)
  22. Check EGR system for proper operation.
  23. 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 TESTS W/CODES article below.
  2. «TESTS W/CODES - 2.2L»(ref-20062)
  3. «TESTS W/CODES - 3.1L»(ref-20067)
  4. «TESTS W/CODES - 3.8L»(ref-20071)
  5. «TESTS W/CODES - 4.3L»(ref-20077)
  6. «TESTS W/CODES - 5.0L»(ref-20082)
  7. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)
  8. Check EGR system.
  9. Check park/neutral switch.
  10. 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 appropriate BASIC TESTING article below.
  3. «BASIC TESTING - 2.2L»(ref-20060)
  4. «BASIC TESTING - 3.1L»(ref-20065)
  5. «BASIC TESTING - 3.8L»(ref-20072)
  6. «BASIC TESTING - 4.3L»(ref-20075)
  7. «BASIC TESTING - 5.0L»(ref-20080)
  8. «BASIC TESTING - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-57l)
  9. «BASIC TESTING - 7.4L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-74l)
  10. Check engine compression.
  11. Check transmission shift pattern and downshift operation.
  12. Check TCC system for proper operation.
  13. Check for dragging brakes.
  14. Check cooling system thermostat for proper heat range and operation.
  15. Ensure initial ignition timing is properly set. Check EST and ESC for proper operation.
  16. Remove spark plugs, and check for wet/fouled spark plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
  17. Check for fuel pressure too high.
  18. Check for fuel pressure regulator leaking into intake manifold.
  19. Check ECT sensor for shift in calibration. See COOLANT TEMPERATURE RESISTANCE VALUES table in the «SENSOR RANGE CHARTS»(/gmc/suburban/i-1992-1999/remont/sensor-range-charts/#engine-controls-sensor-operating-range-charts) article in the ENGINE PERFORMANCE section.
  20. Check Oxygen Sensor (O2S) for silicone or lead contamination.
  21. Ensure speedometer is properly calibrated.
  22. 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.

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 TESTS W/CODES article below.
  5. «TESTS W/CODES - 2.2L»(ref-20062)
  6. «TESTS W/CODES - 3.1L»(ref-20067)
  7. «TESTS W/CODES - 3.8L»(ref-20071)
  8. «TESTS W/CODES - 4.3L»(ref-20077)
  9. «TESTS W/CODES - 5.0L»(ref-20082)
  10. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

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 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 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 TESTS W/CODES article 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 TESTS W/CODES article.
  20. «TESTS W/CODES - 2.2L»(ref-20062)
  21. «TESTS W/CODES - 3.1L»(ref-20067)
  22. «TESTS W/CODES - 3.8L»(ref-20071)
  23. «TESTS W/CODES - 4.3L»(ref-20077)
  24. «TESTS W/CODES - 5.0L»(ref-20082)
  25. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)
  26. Check EGR valve for not working.
  27. 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 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. See DIAGNOSTIC AIDS in DTC 45 chart in appropriate TESTS W/CODES article below.
  5. 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 TESTS W/CODES article below.
  6. «TESTS W/CODES - 2.2L»(ref-20062)
  7. «TESTS W/CODES - 3.1L»(ref-20067)
  8. «TESTS W/CODES - 3.8L»(ref-20071)
  9. «TESTS W/CODES - 4.3L»(ref-20077)
  10. «TESTS W/CODES - 5.0L»(ref-20082)
  11. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

SYMPTOMS

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

Engine Lacks Power

Check probable causes No. 1, 3, 4, 6-11 and 16-21.

Black Smoke

Check probable causes No. 2-4, 6-11 and 16-20.

Blue Smoke

Check probable causes No. 2, 6-8, 13-15 and 17-20.

Excessive Oil Consumption

Check probable causes No. 2, 6-8, 13-15 and 17-20.

Noisy Operation

Check probable causes No. 1-8, 11-12 and 19-20.

Cyclic Sound From Turbocharger

Check probable causes No. 2, 19 and 20.

Oil Leak At Turbine Seal

Check probable causes No. 13-15 and 17-20.

Oil Leak At Compressor Seal

Check probable causes No. 2, 8-11, 13-15 and 17-20.

PROBABLE CAUSES

  1. Clogged air filter element.
  2. Obstructed air intake duct to turbo compressor.
  3. Obstructed air outlet duct from compressor to intake manifold.
  4. Obstructed intake manifold.
  5. Air leak in duct from air cleaner to compressor.
  6. Air leak in duct from compressor to intake manifold.
  7. Air leak at intake manifold-to-engine joint.
  8. Obstruction in exhaust manifold.
  9. Obstruction in exhaust system.
  10. Gas leak in exhaust manifold-to-engine joint.
  11. Gas leak in turbine inlet-to-exhaust manifold joint.
  12. Gas leak in ducts after turbine outlet.
  13. Obstructed turbocharger oil drain line.
  14. Obstructed engine crankcase ventilation.
  15. Turbocharger center housing sludged or coked.
  16. Engine camshaft timing incorrect.
  17. Worn engine piston rings or liners (blow-by).
  18. Internal engine problems (valves, pistons).
  19. Dirt caked on compressor wheel and/or diffused vanes.
  20. Damaged turbocharger.
  21. Wastegate stuck open.

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.

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 self-diagnostic codes. Use test results to identify faulty component or circuit.

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

Possible Causes & Corrections

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 loss of trouble code memory. To check code, disconnect TP sensor, and run engine at idle until Malfunction Indicator Light (MIL) comes on. Code 22 should be stored and retained in memory when ignition is turned off. If not, PCM is faulty.
  7. 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.
  8. Check for aftermarket parts which may not have been produced to manufacturers' specifications. Solenoids without original -equipment diodes for circuit protection and HEI-EST module 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.
  9. Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
  10. 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.
  11. Check for intermittent short to ground on terminal "B" (diagnostic enable) of Data Link Connector (DLC) or in Malfunction Indicator Light (MIL) circuit.
  12. On vehicles not equipped with a driver information center, use scan tester to check for intermittent wiring problem. See SCAN TESTER USAGE in appropriate TESTS W/CODES article.
  13. «TESTS W/CODES - 2.2L»(ref-20062)
  14. «TESTS W/CODES - 3.1L»(ref-20067)
  15. «TESTS W/CODES - 3.8L»(ref-20071)
  16. «TESTS W/CODES - 4.3L»(ref-20077)
  17. «TESTS W/CODES - 5.0L»(ref-20082)
  18. «TESTS W/CODES - 5.7L»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

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