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Home >> Oldsmobile >> 1997 >> Cutlass Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 3.1L Engine >> Diagnostic Trouble Codes >> DTC P0300-P0306 - Engine Misfire Detected >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING - 3.1L article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Is DTC P1200 also set? If yes, go to DTC P1200 - INJECTOR CONTROL CIRCUIT . If no, go to next step.
  3. Start and idle engine. Review and record scan tool Freeze Frame data. Operate vehicle to duplicate the conditions present when the DTC was set (as defined by the Freeze Frame data). Monitor the scan tool Misfire Cur. # display for each cylinder. Does Misfire Cur. # display increment for any cylinder (indicating a misfire currently occurring)? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  4. Does Misfire Hist. # display a very large value for more than one cylinder? If yes, go to next step. If no, go to step  14.
  5. Visually and physically inspect the vacuum hoses for splits, kinks, and improper connections. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  6. Visually and physically inspect the PCV valve for improper installation and for damaged "O" rings. If a problem is found, repair as necessary. After repairs, go to step  30. If no, problem was found, go to next step.
  7. Inspect throttle body inlet screen for damage or for presence of foreign objects that may partially block the air flow sample through the MAF sensor. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  8. Check fuel pressure. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  9. Check fuel for excessive water, alcohol, or other contaminants. If a problem was found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  10. Visually and physically inspect the PCM injector grounds, power grounds and sensor grounds to ensure that they are clean, tight, and in their proper locations. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  11. Disconnect the MAF sensor electrical connector. Operate vehicle to duplicate the conditions present when the DTC was set (as defined by the Freeze Frame data). Monitor the scan tool Misfire Cur. #. display for each cylinder. Does Misfire Cur. # display increment for any cylinder (indicating a misfire currently occurring)? If yes, go to next step. If no, go to step  27.
  12. Visually and physically inspect for vacuum leaks in intake manifold, EGR adapter, EGR valve, EGR feed pipes and injector "O" rings. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  13. Remove EGR valve. Visually/physically inspect EGR valve to ensure that pintle is not sticking partially open. Also, inspect EGR valve pintle and seat for carbon deposits or burrs that may interfere with the pintle closing completely. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  14. Check for proper injector operation. Install Injector Harness Load Tester (J 34730-380) using Load Tester Adaptor (J 34730-385) to 10-Way Fuel Injector Harness Connector. While observing Fuel Injector Coil/Balance Tester (J 39021), attempt to start engine. Do all LEDs for cylinders 1-6 flash? If yes, go to next step. If no, go to step  16.
  15. Check for proper fuel injector operation. If a problem is found, repair as necessary. After repairs, go to step  30. If no, go to step  17.
  16. Check affected Injector Driver circuit(s) from PCM for opens, shorted to ground or poor connections. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to step  29.
  17. Visually and physically inspect the ignition wires associated with the cylinder(s) which were misfiring to ensure that they are not damaged and are connected to the proper cylinders at the coils and at the spark plugs. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  18. Install Spark Tester (J 26792) at spark plug end of the ignition wire for the cylinder that is indicated by the Misfire Cur Counters or Misfire Hist. Counters as having the most severe misfire (largest number of counts). Jumper spark plug end of the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil (i.e., 1/4; 2/5; 3/6). Crank engine while observing spark tester. A crisp, Blue spark should be observed. Is adequate spark present? If yes, go to step  23. If no, go to next step.
  19. Remove and visually/physically inspect the ignition coil(s) associated with the cylinders that were indicated as misfiring. Ensure that the coil(s) and coil towers are free of cracks and carbon tracking. If a problem is found, replace damaged ignition coil(s) as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  20. Measure the ignition coil secondary resistance. If resistance is outside the specified value of 5000-8000 ohms, replace faulty ignition coil(s) as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  21. Remove and visually/physically inspect the ignition wires associated with the cylinders that were indicated as misfiring. Ensure that the wires and boots are free of carbon tracking and the insulation is not damaged. If a problem is found, replace faulty ignition wire(s) as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  22. Measure the resistance of the ignition wires associated with the cylinders that were indicated as misfiring. Replace any ignition wire(s) that measure greater than 30,000 ohms. After repairs, go to step  30. If no problem was found, go to step  28.
  23. Remove spark plugs from the cylinders that were indicated as misfiring. Visually inspect spark plug electrodes for excessive fouling. Was a problem found? If yes, diagnose for an engine mechanical problem. If no, go to next step.
  24. Visually inspect spark plug insulators for cracks, carbon tracking, or other damage. If a problem is found, replace faulty spark plug(s) as necessary. After repairs, go to step  30. If no problem is found, go to next step.
  25. Check for an engine mechanical problem. If a problem is found, repair as necessary. After repairs, go to step  30. If no problem was found, go to next step.
  26. Check for a transaxle TCC problem. If a problem is found, repair transaxle as necessary. After repairs, go to step  30. If no problem was found, see DIAGNOSTIC AIDS .
  27. Replace MAF sensor. After replacing sensor, go to step  30.
  28. Replace ignition control module. After replacing module, go to step  30.
  29. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  30. 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, system is okay.
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