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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 67 (Engine Controls Self-Diagnostics - 4.3L) >> Diagnostic Tests >> DTC P0300-P0306: Engine Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Savana and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn ON the ignition, with the engine OFF. Observe the DTC information with a scan tool. Are there any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Start the engine. Clear the DTCs with a scan tool. Allow the engine to reach operating temperature. Observe the Misfire Current Counters with a scan tool. Are any of the Misfire Current Counters incrementing? If yes, go to step  5. If no, go to next step.
  4. Observe the Freeze Frame/Failure records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. Is the engine misfiring? If yes, go to next step. If no, see appropriate article in ENGINES.
  6. Is there only one Misfire Current Counter incrementing? If yes, go to next step. If no, go to step  13.
  7. Turn OFF the ignition. Disconnect the spark plug wire from the spark plug. Connect the J 26792 Spark Tester to the spark plug wire and a good ground. Start and idle the engine. Does the spark tester spark and is the spark consistent? If yes, go to step  9. If no, go to next step.
  8. Turn OFF the ignition. Remove the spark plug wire from the cylinder that indicates a misfire. Measure the resistance of the spark plug wire with a Digital Multimeter (DMM). Is the resistance less than 625 ohms Per Foot (Per 30 CM)? If yes, go to step  16. If no, go to step  15.
    9. NOTE: If the spark plug is gas, coolant, or oil fouled, determine the cause of the fouling. See DTC P0172 & P0175: FUEL TRIM SYSTEM RICH - BANK 1 & 2  for spark plugs that are gas fouled. If spark plugs that are coolant or oil fouled, repair engine as necessary.
  9. Remove the spark plug from the cylinder that indicates a misfire. Inspect the spark plug. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
  10. Exchange the suspected spark plug with another cylinder that is operating correctly. Start the engine. Operate the engine within the conditions that the misfire occurred. Monitor the Misfire Current Counters with a scan tool. Did the misfire move with the spark plug? If yes, go to step  14. If no, go to next step.
    11. NOTE: Make sure all the injectors operate. High resistance in an injector circuit causes the injector to be inoperative without setting a fuel injector DTC. Return to this diagnostic after you complete the Fuel Injector Coil Test.
  11. Perform the Fuel Injector Coil Test. See appropriate SYSTEM & COMPONENT TESTING article. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
  12. Perform the Fuel System Diagnosis. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Did you find and correct the condition? If yes, go to step  17. If no, see appropriate article in ENGINES.
  13. Inspect or test for the following conditions:
    • Inspect the vacuum hoses for splits, kinks, and the correct connections.
    • Inspect for vacuum leaks at the throttle body and at the intake manifold.
    • Inspect the PCM grounds for being clean, tight, and in the correct location.
    • Inspect for contaminated fuel.
    • Test for the correct fuel pressure. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
    • Inspect for poor connections at the ignition coil.
    • Inspect for faulty spark plug wires or coil wire.
    • Inspect for fouled or damaged spark plugs.
    • Inspect the distributor cap and distributor for damage.
    • Test the ignition coil for the correct output with the J 26792 Spark Tester.
    • Inspect the exhaust system for restrictions.

    Did you find and correct the condition? If yes, go to step  17. If no, see appropriate article in ENGINES.

  14. Replace the spark plugs. After repairs, go to step  17.
  15. Replace the spark plug wires. After repairs, go to step  17.
  16. Replace the distributor cap. After repairs, go to next step.
  17. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  18. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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