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Home >> Oldsmobile >> 1996 >> Eighty-Eight Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0300 - Engine Misfire Detected >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. If DTC P1200 is also set, go to DTC P1200. If DTC P1200 is not set, go to next step.
  3. Start engine and allow it to idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, go to next step. If MISFIRE CUR # is not increasing, see DIAGNOSTIC AIDS.
  4. If MISFIRE HIST # displays a very large number for more than one cylinder, go to next step. If MISFIRE HIST # does not display a very large number for more than one cylinder, go to step 14).
  5. Check vacuum hoses for splits, kinks, or improper connections. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  6. Check PCV valve for improper installation or damaged "O" rings. If a problem is found, go to step 27). If no problem is found, go to next step.
  7. Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  8. Perform A-7, INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  9. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination and go to step 27). If fuel is okay, go to next step.
  10. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  11. Disconnect MAF sensor harness connector. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, go to next step. If MISFIRE CUR # is not increasing, go to step 25).
  12. Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  13. Remove EGR valve and inspect valve, seat and passages for damage. Inspect valve pintle to ensure it is not sticking partially open. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  14. Perform A-4, INJECTOR CIRCUIT TEST under FUEL SYSTEM DIAGNOSIS in BASIC TESTING article. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  15. Check ignition wire(s) associated with cylinder(s) that is misfiring. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  16. Install a spark tester on spark plug wire at spark plug end for cylinder indicating most severe misfire. Connect a jumper wire between engine ground and companion cylinder spark plug wire at spark plug end. Companion cylinders are 1 and 4, 2 and 5, and 3 and 6. Crank engine and check for crisp, Blue spark at tester. Repeat procedure for each affected cylinder. If spark is okay on all cylinders, go to step 21). If spark is not okay on any cylinder, go to next step.
  17. Remove ignition coil(s) associated with misfiring cylinder(s). Check ignition coils for cracks or carbon tracking. If a problem is found, replace damaged coil(s) and go to step 27). If no problem is found, go to next step.
  18. Check ignition coil secondary resistance. If resistance is not 5000-8000 ohms, replace ignition coil and go to step 27). If resistance is as specified, go to next step.
  19. Remove ignition wire(s) associated with misfiring cylinder(s). Check ignition wire(s) boot for carbon tracking or damaged insulation. If a problem is found, replace faulty ignition wire(s) and go to step 27). If no problem is found, go to next step.
  20. Check resistance of ignition wire(s) associated with misfiring cylinder(s). If resistance is more than 30,000 ohms, replace ignition wire(s) and go to step 27). If resistance is 30,000 ohms or less, go to step 26).
  21. Remove spark plug(s) associated with misfiring cylinder(s). Check spark plugs for excessive fouling. If spark plugs are excessively fouled, diagnose and repair mechanical engine problem. If spark plugs are not excessively fouled, go to next step.
  22. Check spark plug insulation for cracks, carbon tracking or other damage. If a problem is found, replace faulty spark plug(s) and go to step 27). If no problem is found, go to next step.
  23. Diagnose mechanical engine problem. If a problem is found, repair as necessary and go to step 27). If no problem is found, go to next step.
  24. Check for transmission DTCs. If a problem is found, repair as necessary and go to step 27). If no problem is found, see DIAGNOSTIC AIDS.
  25. Replace MAF sensor and go to step 27).
  26. Replace ignition control module and go to next step.
  27. Using scan tool, read and record FREEZE FRAME data. Clear DTCs. Start engine and allow it to idle. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, return to step 2). If MISFIRE CUR # is not increasing, repair is complete.
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