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Engine Controls - Trouble Shooting - No Codes - 4.3l Chevrolet Chevy Express H2500

Testing & Diagnostics ~4623 words

INTRODUCTION

Before diagnosing symptoms or intermittent faults, follow proper workflow. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. If no Diagnostic Trouble Codes (DTC) are present and a no-start condition exists, proceed to NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article. If no DTCs are present and a driveability condition exists, diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

Use intermittent test procedures to locate driveability problems that do not occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present but no problem was found during self-diagnostic testing.

PRELIMINARY INSPECTION

  1. Verify on-board diagnostics are working by performing «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  2. Ensure PCM and MIL functions properly.
  3. Ensure no DTCs (except intermittent) are stored.
  4. Ensure fuel control system operates properly. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  5. Perform fuel system pressure test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  6. Visually inspect all systems.

After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. See SYMPTOMS .

SYMPTOMS

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

Note. If PCM displays data but engine fails to start, see NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.

SYMPTOM DIAGNOSIS

Symptom checks should not be used unless symptom occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA and SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA articles were performed before diagnosing a symptom. Symptoms available for diagnosis include

  1. «DETONATION/SPARK KNOCK»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  2. «ENGINE BACKFIRES»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  3. «ENGINE CUTS OUT, MISSES»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  4. «ENGINE DIESELING/RUN-ON»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  5. «HARD START»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  6. «HESITATION, SAG OR STUMBLE»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  7. «LACK OF POWER OR SLUGGISH»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  8. «POOR FUEL ECONOMY»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  9. «ROUGH, UNSTABLE OR INCORRECT IDLE & STALLING»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)
  10. «VEHICLE SURGES OR CHUGGLES»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l)

Symptom Definition

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

Possible Causes & Corrections

Check the following items

  1. Low engine coolant level.
  2. Proper tension on the drive belts.
  3. Restricted air flow through the radiator or restricted coolant flow.
  4. Faulty thermostat.
  5. Check for a correct coolant mixture.
  6. Inspect for an Engine Coolant Temperature (ECT) sensor that has a shift in value. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  7. Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the problem.
  8. If system is lean, the long term fuel trim will be more than 150 on scan tool.
  9. Check fuel pressure. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  10. Inspect for a poor fuel quality and a proper octane rating.
  11. If fuel trim readings are normal and there are no engine mechanical concerns, fill fuel tank with a known-good fuel and re-evaluate vehicle performance.
  12. Inspect spark plugs for proper heat range and gap.
  13. Check Knock Sensor (KS) system for excessive spark retard activity.
  14. Inspect ignition timing.
  15. Inspect for carbon build up. Remove carbon with a top engine cleaner.
  16. Test combustion chamber pressure by performing a compression test. See CYLINDER COMPRESSION PRESSURE «MECHANICAL INSPECTION»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  17. Check for proper operation of EGR valve.
  18. Test the Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. TCC applying too soon can cause engine to spark knock.
  19. Check Service Bulletins for calibration updates.

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

Check the following items

  1. Inspect ignition system.
  2. Check for crossfire between spark plugs, such as the distributor cap, spark plug wires, and proper routing of the plug wires.
  3. Check engine for low compression. See CYLINDER COMPRESSION PRESSURE «MECHANICAL INSPECTION»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article. Low compression can be caused by improper valve timing, faulty manifold gaskets, sticking or leaking valve.
  4. Check intake and exhaust system for fresh air entering exhaust upstream of the catalytic converter or restrictions.
  5. Check fuel system performance. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  6. Perform fuel injector balance test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  7. Check AIR system for proper operation, if applicable.

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 under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.

Check the following items

  1. Start engine.
  2. Allow engine to stabilize.
  3. Disconnect Idle Air Control (IAC) motor.
  4. Perform Cylinder Power Balance Test with a scan tool. Do not perform this test for more than 2 minutes to prevent damaging catalytic converter.
  5. If there is an RPM drop on all cylinders, equal to within 50 RPM, refer to «ROUGH, UNSTABLE OR INCORRECT IDLE & STALLING»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l) .
  6. Reconnect IAC motor with ignition off.
  7. If there is no RPM drop on one or more of the cylinders, or excessive variation in drop, check for spark on the suspected cylinders with Spark Tester (J-26792).
  8. If there is no spark, refer to «DISTRIBUTOR IGNITION SYSTEM»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  9. If there is spark, remove spark plugs in affected cylinders and check for insulation cracks, wear, improper gap, burned electrodes or heavy deposits. Check spark plug wire resistance. The resistance should not exceed 1000 ohms per foot. Check distributor rotor and cap. If previous check did not find the problem, visually check ignition system for moisture, dust, cracks, burns, etc. With the engine running, spray the plug wires with a fine water mist to check for shorts. Perform the Fuel Injector Balance Test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  10. Perform cylinder compression check. See CYLINDER COMPRESSION PRESSURE «MECHANICAL INSPECTION»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  11. Check engine for improper valve timing, bent pushrods, worn rocker arms, worn camshaft lobes or broken/weak valve springs.
  12. Perform Fuel Injector Balance Test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  13. Check intake and exhaust manifold passages for casting flash.
  14. Check fuel pressure. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  15. Inspect for water contamination in fuel.
  16. Perform fuel injector coil test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  17. Perform fuel injector balance test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  18. Check for Electromagnetic Interference (EMI).
  19. Check routing of secondary wires and ground circuit.

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

Check for the following

  1. Inspect the Evaporative Emission (EVAP) system and fuel tank venting.
  2. Inspect fuel injectors for leakage or diagnose fuel system. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.

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

Check the following items

  1. Ensure vehicle operator is using the correct starting procedure.
  2. Monitor Engine Coolant Temperature (ECT) sensor with scan tool. Compare engine coolant temperature with the ambient air temperature on a cold engine. If coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, check for high resistance in the coolant sensor circuit.
  3. Check Throttle Position (TP) sensor. If a sticking throttle shaft or binding linkage causes a high TP sensor voltage or an open throttle indication, the control module will not control the idle. While monitoring the TP sensor voltage, the scan tool should display less than 0.85 volt with throttle closed.
  4. Inspect fuel pump relay for proper operation. The fuel pump should operate for the first 2 seconds after turning ignition on. See Fuel Pump Electrical Circuit Diagnosis under «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  5. Check fuel pressure. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  6. Inspect for water contamination in fuel.
  7. Perform fuel injector coil test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  8. Perform fuel injector balance test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  9. Inspect fuel pump check valve. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  10. Check for proper ignition voltage output with a Spark Tester (J-26792).
  11. Inspect spark plugs. Check for wet fouling, cracks, wear, improper gap, burned electrodes or heavy deposits.
  12. Check for bare or shorted ignition wires.
  13. Check for moisture in the distributor cap, if applicable.
  14. Inspect loose ignition coil connections.
  15. Inspect loose ignition control module connections.
  16. Inspect faulty control module or ignition system grounds.
  17. Improper valve timing.
  18. Low compression.
  19. Bent pushrods.
  20. Worn rocker arms.
  21. Broken or weak valve springs.
  22. Worn camshaft lobes.
  23. Check intake and exhaust manifolds for casting flash.
  24. Check Idle Air Control (IAC) operation. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  25. Inspect for a restricted exhaust. See «RESTRICTED EXHAUST»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l__restricted-exhaust) .

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.

Check for the following items

  1. Check fuel pressure. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  2. Inspect Throttle Position (TP) sensor for binding or sticking. Voltage should increase at a steady rate as the throttle moves toward Wide Open Throttle (WOT) position.
  3. Inspect Manifold Absolute Pressure (MAP) sensor response and accuracy. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  4. Test canister purge system for proper operation. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  5. Perform fuel injector coil test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  6. Perform fuel injector balance test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  7. Test for low fuel pressure after a cold start or during a moderate or full throttle acceleration.
  8. Check for damaged spark plug wires.
  9. Inspect for fouled spark plugs.
  10. Inspect for proper ignition system performance.
  11. Search for Service Bulletins for calibration updates.
  12. Test generator output voltage.
  13. Inspect for a restricted exhaust. See «RESTRICTED EXHAUST»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l__restricted-exhaust) .

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

Check the following items

  1. Compare customer vehicle with a similar unit. Verify the customer's concern.
  2. Remove air filter and check for dirt or a restriction.
  3. Inspect transmission shift pattern and downshift operation.
  4. Inspect for a restricted fuel filter, contaminated fuel, or improper fuel pressure. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  5. Perform the fuel injector balance test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  6. Inspect exhaust system for a possible restriction. See «RESTRICTED EXHAUST»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l__restricted-exhaust) .
  7. Inspect exhaust system for damaged or collapsed pipes. Inspect the muffler for heat distress or a possible internal failure.
  8. Inspect control module grounds for being clean, tight, and in their proper location.
  9. Inspect Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
  10. Inspect A/C operation. See appropriate MANUAL or AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.
  11. Test generator output voltage.
  12. Monitor Knock Sensor (KS) system for retarded timing. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  13. Engine compression. See CYLINDER COMPRESSION PRESSURE «MECHANICAL INSPECTION»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article. Low compressions can be caused by faulty valve timing or improper or worn camshaft.

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

Check the following items

  1. Inspect the air cleaner element or filter, for dirt or being plugged.
  2. Visually and physically check the vacuum hoses for splits, kinks, and proper connections as shown on the underhood Vehicle Emission Control Information label.
  3. Discuss the driving habits with the owner. Check if A/C is ON full time or defroster mode is ON? Check tires for proper inflation. Check that wheel and tires are the correct size. Check for excessively heavy loads being carried or an aggressive driving habits
  4. Suggest to owner to fill the fuel tank and observe fuel economy.
  5. Suggest to owner to refer to Important Facts on Fuel Economy in the owner's manual.
  6. Inspect fuel type, quality and alcohol content.
  7. Check fuel pressure. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  8. Inspect spark plugs. Remove and check for wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
  9. Inspect for an open Ignition Control (IC) circuit.
  10. Check ignition wires for cracking, hardness and proper connections.
  11. Inspect Knock Sensor (KS) system operation. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  12. Inspect engine coolant level.
  13. Inspect engine thermostat for being open or for wrong heat range.
  14. Inspect transmission shift pattern.
  15. Inspect Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
  16. Inspect for proper calibration of the speedometer.
  17. Inspect for dragging brakes.

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

Check the following items

  1. Inspect the Heated Oxygen Sensor (HO2S). Check for silicone contamination from fuel or improperly used sealant. The sensor will have a White powdery coating. The sensor will result in a high but false signal voltage or rich exhaust indication. The control module will reduce the amount of fuel delivered to the engine causing a severe driveability condition.
  2. Inspect Engine Coolant Temperature (ECT) sensor using scan tool in order to compare the engine coolant temperature with the ambient air temperature on a cold engine. If coolant temperature reading is more than 5 degrees more than or less than the ambient air temperature on a cold engine, test for a high resistance in the coolant sensor circuit or the sensor itself. Inspect the Manifold Absolute Pressure (MAP) sensor response and accuracy.
  3. Check fuel pressure. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  4. Determine if a rich or lean system causes the condition. Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the condition. Using scan tool, observe fuel trim conditions. A lean condition will indicate a long term fuel trim of more than 150 on scan tool. A rich condition will indicate a long term fuel trim of less than 115 on scan tool.
  5. Perform fuel injector balance test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  6. Test fuel injector driver circuit. Disconnect injector harness connector. Connect an injector test light between the terminals of each injector connector and observe test light while cranking. If test light fails to blink at any connector, injector drive circuit harness connector or terminal is faulty.
  7. Perform fuel injector coil test. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  8. Inspect Evaporative Emission (EVAP) control system. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
  9. Check ignition output using Spark Tester (J-26792).
  10. Inspect spark plugs. Check for wet plugs, cracks, wear, improper gap, burned electrodes, blistered insulators or heavy deposits.
  11. Check spark plug wires. Resistance should be 30,000 ohms per foot.
  12. Inspect for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low Idle Air Control (IAC) counts.
  13. Inspect control module grounds for being clean, tight and in their proper locations.
  14. Observe scan tool to determine if the control module is receiving an A/C signal. If a condition exists with the A/C ON, inspect the A/C system operation.
  15. Check EGR being ON while idling which will cause roughness, stalling and hard starting.
  16. Inspect battery cables and ground straps for being clean and secure.
  17. Inspect the crankcase ventilation valve for proper operation by placing a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace PCV.
  18. Broken motor mounts.
  19. Improper valve timing.
  20. Low compression.
  21. Worn rocker arms.
  22. Broken or weak valve springs or worn camshaft lobes.

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

Check for the following items

  1. Ensure driver understands the torque converter clutch operation and A/C compressor operation.
  2. Ensure that transmission fluid is at proper level.
  3. Display scan tool parameters for the various engine controls sensors. Inspect for any abnormal readings.
  4. Inspect for a rich or lean symptom that causes the condition. Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the condition.
  5. Lean condition. The long term fuel trim will be more than 150 displayed on scan tool.
  6. Rich condition. The long term fuel trim will be less than 115 displayed on scan tool.
  7. Check fuel pressure while the condition exists. See «FUEL SYSTEMS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.
  8. Inspect in-line fuel filter for restrictions.
  9. Check for proper ignition output voltage using Spark Tester (J-26792). Inspect spark plugs. Remove plugs and inspect for wetness, cracks, wear, improper gap, burned electrodes or heavy deposits.
  10. Check the secondary ignition system and spark plugs. Remove plugs and inspect them for wetness, cracks, wear, improper gap, burned electrodes or heavy deposits.
  11. Check for a loose or damaged Crankshaft Position (CKP) sensor and reluctor wheel.
  12. Inspect control module grounds for being clean, tight, and in their proper locations.
  13. Test generator output voltage.
  14. Inspect vacuum hoses for kinks or leaks.
  15. Check for an intermittent EGR problem.
  16. Inspect TCC operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
  17. Inspect exhaust system for a possible restriction. See «RESTRICTED EXHAUST»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l__restricted-exhaust) .

RESTRICTED EXHAUST

For dual exhaust systems a quick check of exhaust flow will help determine which side of the exhaust system is restricted. The side that has less exhaust flow is the side that will be suspect, and diagnosis should begin there. To diagnose exhaust system, see EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L CHEVY EXPRESS & SAVANA article.

INTERMITTENTS

Note. Intermittent is a DTC or symptom, with a condition that cannot be duplicated.

PRELIMINARY

Perform the Diagnostic System Check - Engine Controls before starting. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.

HARNESS OR CONNECTOR INTERMITTENTS

Many intermittent open or shorted circuits come and go with harness or connector movement caused by the following type conditions

  1. Vibration.
  2. Engine torque.
  3. Bumps or rough pavement.

Test for intermittents by performing the applicable procedure from the following list

  1. Move related connectors and wiring while monitoring the appropriate scan tool data.
  2. Move related connectors and wiring with the component commanded on and off, with scan tool. Observe the component operation.
  3. With the engine running, move related connectors and wiring while monitoring engine operation.

Verify whether the harness or connector movement affects any of the following systems

  1. Data displayed.
  2. Component or system operation.
  3. Engine operation.

Repair components as necessary.

ELECTRICAL CONNECTIONS OR WIRING

  1. Intermittents are usually caused by one or more of the following conditions: Poor electrical connections. Terminal tension. Wiring problems.
  2. Carefully inspect the suspected circuit for the following conditions: Poor mating of the connector halves. Terminals backed out or not fully seated in the connector body. Improperly formed or damaged terminals. Test for poor terminal tension. Poor terminal-to-wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body. Corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation, with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits. Wires that are broken inside the insulation. Pinched, cut or rubbed-through wiring in harness. Wiring that is in contact with hot exhaust components.
  3. Repair the condition as necessary.

CONTROL MODULE POWER & GROUNDS, & COMPONENT POWER & GROUNDS

Poor power or ground connections can cause widely varying symptoms.

  1. Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test light or a Digital Volt-Ohmmeter (DVOM) may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. See POWER DISTRIBUTION in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
  2. Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. See GROUND DISTRIBUTION in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

TEMPERATURE SENSITIVITY

  1. An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot.
  2. The following data may help to diagnose this type of intermittent condition: Freeze Frame/Failure Records. Scan tool snapshot. Vehicle data recorder.
  3. If the intermittent is related to heat, review the following data: High ambient temperatures. Underhood or engine generated heat. Circuit generated heat due to a poor connection, or high electrical load. Higher than normal load conditions, such as towing.
  4. If the intermittent is related to cold, review the following data: Low ambient temperatures. In extremely low temperatures, ice may form in a connection or component. Test for water intrusion. The condition only occurs on a cold start. The condition is not present after the vehicle warms up.
  5. Information from the customer may help to determine if the trouble follows a pattern that is temperature related.

ELECTROMAGNETIC INTERFERENCE & ELECTRICAL NOISE

Some electrical components or circuits are sensitive to Electromagnetic Interference (EMI) or other types of electrical noise. Perform the following procedures

  1. Inspect for a misrouted harness that is too close to a high voltage or high current device. This condition may induce electrical noise on a circuit that could interfere with normal circuit operation. Inspect for wires that are too close to the following devices: Secondary ignition components. Motors. The generator.
  2. Determine whether the electrical system interference is caused by a malfunctioning relay, PCM driven solenoid or switch. These components may cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
  3. Determine whether non-factory or aftermarket add-on accessories are installed in the vehicle. These accessories may lead to an emission related OBD-II failure. Determine if any of the following non-factory or aftermarket add-on accessories is causing the intermittent: Lights. 2-way radios. Amplifiers. Electric motors. Remote starters. Alarm systems. Cellular phones.
  4. Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode.
  5. Test for proper performance of the generator. See ON-VEHICLE TESTING in appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
  6. If a DTC is determined to be intermittent and the tests do not reveal a problem, see «VEHICLE DATA RECORDER»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l__vehicle-data-recorder) .

INCORRECT PCM PROGRAMMING

  1. There are only a few situations when reprogramming a PCM is appropriate, such as the following: A new service PCM is installed. A PCM from another vehicle is installed. Revised software or calibration files have been released for this vehicle.
  2. Verify that the PCM contains the correct software or calibration. If incorrect programming is found, reprogram the PCM with the most current software or calibration. See «POWERTRAIN CONTROL MODULE»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__powertrain-control-module) under PROGRAMMING in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.

DUPLICATING FAILURE CONDITIONS

  1. If none of the previous tests are successful, attempt to duplicate or capture the failure conditions.
  2. Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. Perform the following procedure: Review and record Freeze Frame/Failure Records data. Clear DTCs using scan tool. Turn ignition off and wait 15 seconds. Operate vehicle under the same conditions that were noted in Freeze Frame/Failure Records data, as closely as possible. The vehicle must also be operating within the Conditions for Running DTC. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
  3. An alternate method is to drive vehicle with DVOM connected to a suspected circuit. An abnormal reading on the DVOM when problem occurs, may help you locate the problem.

SCAN TOOL SNAPSHOT

The scan tool can be set up to take a snapshot of the parameters available via serial data. The snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when a DTC sets. An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further. Refer to scan tool user instructions for more information on the Snapshot function.

VEHICLE DATA RECORDER

The Vehicle Data Recorder (J-42598) is connected to the Data Link Connector (DLC) and sent with customer. The vehicle data recorder captures data for later retrieval and analysis by the technician. Refer to vehicle data recorder user instructions for more information.

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