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Home >> Chevrolet >> 2000 >> Venture Plus >> 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. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. Check for any other DTCs that are set. Diagnose affected DTC(s). If no other DTCs are set, go to next step.
  3. Start and operate engine at idle. Using scan tool, review and record FREEZE FRAME data. Operate vehicle within conditions for setting this DTC. Monitor Misfire Current Cyl # display for each cylinder. If Misfire Current # display is incrementing for any cylinder (indicating a misfire currently occurring), go to step  5. If Misfire Current # display is not incrementing for any cylinder, go to next step.
  4. View Misfire History Cyl # display on scan tool. If Misfire History Cyl # display a very large value for more than one cylinder, go to next step. If Misfire History Cyl # does not display a very large value for more than one cylinder, go to step  8.
  5. If misfire values displayed on Misfire History Cyl # related to companion cylinders, go to step  9. If misfire values displayed on Misfire History Cyl # is not related to companion cylinders, go to next step.
  6. Check vacuum hoses for improper connections and damage. Check spark plug wire connections at coils and spark plugs. Check engine and PCM grounds. Ensure that connections are clean, tight and in their proper locations. Check EGR to intake manifold piping for proper connections and signs of damage. Repair as necessary. After repairs, go to step  22. If no problems were found, go to next step.
  7. Check fuel pressure. If fuel pressure 52-59 psi (3.6-4.2 kg/cm2 ), go to next step. If fuel pressure is not 52-59 psi (3.6-4.2 kg/cm2 ), diagnose fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  8. Check for proper fuel injector operation. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. After repairs, go to step  22. If no problems were found, go to next step.
  9. Visually inspect ignition wires and coils associated with misfiring cylinders for carbon tracking/arching and damage, connected to incorrect cylinders at coil and spark plug, poor terminal connections at coil and spark plug. Replace affected ignition wire and associated ignition coil. After repairs, go to step  22. If no problems were found, go to next step.
  10. Using a spark tester (J 26792) at spark plug end of ignition wire associated with misfiring cylinders, jumper spark plug end of companion cylinder ignition wire to engine ground. Crank engine while observing spark tester. If spark is present, go to step  15. If spark is not present, go to next step.
  11. Check resistance of ignition wires associated with cylinders that were indicated as misfiring. Resistance should be 600 ohms per foot. Replace ignition wires as necessary. After repairs, go to step  22. If ignition wire are okay, go to next step.
  12. Check resistance of secondary ignition coils associated with misfiring cylinders. Resistance should be 5000-8000 ohms. Replace secondary ignition coil as necessary. After replacing coils, go to step  22. If resistance is as specified, go to next step.
  13. Remove ignition coils associated with misfiring cylinders. Check coils for signs of carbon tracking, cracks, or other damage. Replace affected coils as necessary. After replacing coils, go to step  22. If coils are okay, go to next step.
  14. Leave ignition coils disconnected. Connect a test light across ignition module primary circuit terminals. Remove fuel injector fuse. Observe test light while cranking engine. If test light blinks, go to step  20. If test light does not blink, go to step 21.
  15. Remove spark plugs from cylinders associated with misfire. Visually inspect spark plug electrodes for excessive fouling. Repair cause of misfire or replace fouled spark plugs. After repairs, go to next step.
  16. Check spark plugs for carbon tracking, cracked or other damage to insulator. Check for spark plug electrode damage or incorrect gap. If carbon tracking is apparent on any of spark plugs, replace affected spark plugs and associated ignition wires. Repair as necessary. After repairs, go to step  22. If no problems were found, go to next step.
  17. Reinstall spark plug. Check engine for any mechanical problems. Repair as necessary. After repairs, go to step  22. If no problems were found, go to next step.
  18. If condition occurs while driving, inspect transmission torque converter clutch for problems. See appropriate OVERHAUL article in AUTOMATIC TRANSMISSIONS. Repair as necessary. After repairs, go to step  22. If no problems were found, go to next step.
  19. Inspect fuel system for contaminants. Repair as necessary. After repairs, go to step  22. If no problems were found, see DIAGNOSTIC AIDS .
  20. Reinstall fuel injector fuse. Replace ignition coils associated with misfiring cylinders. After replacing ignition coil(s), go to step  22.
  21. Reinstall fuel injector fuse. Replace ignition control module. After replacing module, go to next step.
  22. Review and record FREEZE FRAME data. Clear DTCs. Operate vehicle within conditions for setting this DTC. Using scan tool, monitor Misfire Current Cyl # display for each cylinder. If Misfire Current Cyl # display is incrementing for any cylinder (indicating a misfire currently occurring), go to step  2. If Misfire Current Cyl # display is not incrementing for any cylinder, system okay.
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