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Home >> Pontiac >> 2002 >> Aztek FWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0300-P0306: Engine Misfire Detected >> Diagnostic Procedures
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Diagnostic Procedures

  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. Are any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Start and idle the engine. Review and record the scan tool Freeze Frame data. Operate the vehicle to duplicate the conditions present when the DTC was set, as defined by the Freeze Frame data. Monitor the scan tool Misfire Current Cyl # display for each cylinder. Is the Misfire Current # display incrementing for any cylinder, indicating a misfire currently occurring? If yes, go to step  5. If no, go to next step.
  4. View the Misfire History Cyl # display on the scan tool. Does the Misfire History Cyl # display a very large value for more than one cylinder? If yes, go to next step. If no, go to step  8.
  5. Are the misfire values displayed on the Misfire History Cyl # related to companion cylinders, such as 1/4, 2/5, 3/6? If yes, go to step  9. If no, go to next step.
  6. Visually and physically inspect the following components:
    • Excessive vibration from sources other than the engine. Possible sources of vibration are drive belts and variations in brake rotor thickness.
    • The vacuum hoses.
    • The crankcase ventilation system for vacuum leaks.
    • The throttle body and intake manifold for vacuum leaks.
    • The PCM grounds.
    • The spark plug wires.
    • Measure the resistance of the spark plug wires associated with the misfiring cylinders.
    • The Exhaust Gas Recirculation (EGR) valve to exhaust manifold gasket for signs of leaks or damage.
    • The fuel for contamination.

    Did you find and correct the condition? If yes, go to step  18. If no, go to next step.

  7. Install a fuel pressure gauge. Turn ON the ignition, with the engine OFF. With a scan tool, command the fuel pump ON. Monitor the fuel pressure with the fuel pump running. Does the fuel pressure gauge indicate that the fuel pressure is 52-59 psi? If yes, go to next step. If no, diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
  8. Test for proper fuel injector operation. Preform fuel injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. Did you find and correct the condition? If yes, go to step  18. If no, go to next step.
    9. NOTE: If carbon tracking is apparent at either end of the spark plug wires, replace the affected ignition wire and the associated ignition coil.
  9. Visually inspect the ignition wires and coils associated with the misfiring cylinders for the following conditions:
    • Carbon tracking/arching and damage.
    • Connected to the incorrect cylinders at the coil and spark plug.
    • Poor terminal connections at the coil and spark plug.

    If a problem is found, repair as necessary. Did you find and correct the condition? If yes, go to step  18. If no, go to next step.

  10. Install the J 26792 spark tester at the spark plug end of the ignition wire associated with the misfiring cylinders. Jumper the spark plug end of the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil, such as 1/4, 2/5, 3/6. Crank the engine while observing the J 26792. Is spark present? If yes, go to step  15. If no, go to next step.
  11. Measure the resistance of the ignition wires associated with the cylinders that were indicated as misfiring. Replace the ignition wires if the resistance measures more than 3000 ohms per ft (9868 ohms per meter). Did you find and correct the condition? If yes, go to step  18. If no, go to next step.
  12. Measure the resistance of the secondary ignition coils associated with the misfiring cylinders. If the resistance is not 5-8 K ohms, replace the malfunctioning ignition coils. Did you find and correct the condition? If yes, go to step  18. If no, go to next step.
  13. Remove the ignition coils associated with the misfiring cylinders. Inspect the coils for signs of carbon tracking, cracks, or other damage. Did you find and correct the condition? If yes, go to step  18. If no, go to next step.
    14. NOTE: Be sure to reinstall the fuel injector fuse.
  14. Leave the ignition coils disconnected. Connect a test lamp across the ignition module primary circuit terminals. Remove the fuel injector fuse. Observe the test lamp while cranking the engine. Does the test lamp blink? If yes, go to step  16. If no, go to step  17.
  15. Remove the spark plugs from the cylinders associated with the misfire. Inspect the spark plugs. Did you find and correct the condition? If yes, go to step  18. If no, see DIAGNOSTIC AIDS .
  16. Replace the ignition coils associated with the misfiring cylinders. After repairs, go to step  18.
  17. Replace the ignition control module. After repairs, go to next step.
  18. Review and record the Freeze Frame data. Clear the DTCs. Start and idle the engine. Operate the vehicle to duplicate the conditions present when the DTC was set, as defined by the Freeze Frame data. Monitor the scan tool Misfire Current Cyl # display for each cylinder. Is Misfire Current Cyl # display incrementing for any cylinder, indicating a misfire currently occurring? If yes, see appropriate article in ENGINES. If no, system is okay.
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