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Home >> Isuzu >> 1996 >> Hombre S >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Testing >> DTC P0300 - Engine Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
  3. Perform a visual inspection of the following. Check vacuum hoses for splits, kinks and proper routing. Check for leaks at throttle body, intake manifold, EGR valve and PCV system. Check PCM grounds for proper connection. Check injector harness connectors for proper installation. Repair as necessary. If no problems are found, go to next step. After repair is completed, go to step 34).
  4. Start engine and allow it to idle. Using scan tool, select MISFIRE DATA LIST function and monitor MISFIRE CUR. COUNTERS (one counter per cylinder). If any MISFIRE CURRENT counters are incrementing, go to next step. If MISFIRE CURRENT counters are not incrementing, go to step 6).
  5. If all counters noted in step 4) are equal (within one percent of each other), go to step 7). If all counters are not equal, go to step 11).
  6. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If any of MISFIRE CURRENT counters are incrementing, go to step 5). If MISFIRE CURRENT counters are not incrementing, see DIAGNOSTIC AIDS.
  7. Turn ignition off. Install fuel pressure gauge. Start engine and allow it to idle. If fuel pressure is 41-47 psi (284-325 Kg cm2 ), go to next step. If fuel pressure is not 41-47 psi (284-325 Kg cm2 ), see BASIC FUEL SYSTEM CHECKS (A-7) in BASIC TESTING article.
  8. Check for fuel contamination. If fuel is contaminated, go to step 10). If fuel is not contaminated, go to next step.
  9. Check for a basic engine problem (compression, cam timing, throttle body leak, restricted airflow. etc.). Repair as necessary. After repair is completed, go to step 34).
  10. Replace contaminated fuel. After repair has been completed, go to step 34).
  11. Turn ignition off. Disconnect all fuel injector connectors. Install injector test light on injector harness connector for cylinder that misfired. Crank engine and observe test light. If test light flashes, go to next step. If test light does not flash, go to step 13).
  12. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If all injectors are okay, go to step 14). If any injector is not okay, go to step 16).
  13. Remove injector test light. Connect a test light between ground and ignition feed terminal at injector harness connector. Crank engine and observe test light. If test light is on, go to step 17). If test light is off, go to step 26).
  14. Turn ignition off. Disconnect fuel injector harness connector. Install Spark Tester (J-26792) to cylinder No. 1 spark plug wire. Crank engine and check for spark. Repeat spark check for remaining cylinders. If spark is present at all plug wires, go to step 29). If spark is not present at all plug wires, go to step 20).
  15. Turn ignition off. Disconnect fuel injector connector. Disconnect Ignition Control Module (ICM) 6-pin connector. Connect one lead of DVOM to ground. While cranking engine, using other lead of DVOM, probe terminal "D" then terminal "E" at ICM harness connector. If frequency reading is 1-10 Hz, go to step 22). If frequency reading is not 1-10 Hz, go to step 21).
  16. Replace defective fuel injector(s). After repair is completed, go to step 34).
  17. Check suspect fuel injector driver circuit(s) for an open, short to ground or short to voltage. If circuit fault is found, go to next step. If circuit is okay, go to step 19).
  18. Repair open or shorted circuit(s) as necessary. After repair is completed, go to step 34).
  19. Repair open ignition feed circuit as necessary. After repair is completed, go to step 34).
  20. Measure resistance of spark plug wire that spark tester indicated had no spark. If resistance is less than 3000 ohms, go to step 15). If resistance is 3000 ohms or more, go to step 32).
  21. Turn ignition on, with engine off. With DVOM connected to ground, measure voltage at ICM harness connector terminal that frequency was not 1-10 Hz. If voltage is less than .5 volt, go to step 23). If voltage is .5 volt or more, go to step 27).
  22. Remove ignition coil from cylinder that did not have spark. Measure secondary resistance of ignition coil. If resistance is 5000-8000 ohms, go to step 24). If resistance is not 5000-8000 ohms, go to step 30).
  23. Turn ignition off. Connect a test light between positive battery terminal and ICM harness connector terminal that voltage was less than .5 volt. If test light is on, go to step 33). If test light is off, go to step 25).
  24. Install a known-good ignition coil. Reconnect ICM connector. With spark tester connected to spark plug wire of suspect cylinder, crank engine and observe spark tester. If spark is present, go to step 30). If spark is not present, go to step 28).
  25. Repair open in suspect ignition control circuit. After repair is completed, go to step 34).
  26. Repair open ignition feed circuit as necessary. After repair is completed, go to step 34).
  27. Repair short to voltage in suspect ignition control circuit. After repair is completed, go to step 34).
  28. Replace ICM. After repair is completed, go to step 34).
  29. Replace defective spark plug(s) as necessary. After repair is completed, go to step 34).
  30. Replace defective coil. After repair is completed, go to step 34).
  31. Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to step 34).
  32. Replace defective spark plug wire. After repair is completed, go to step 34).
  33. Check for short to ground in ignition control circuits "A" and "B". Repair wiring as necessary. 10). After repair is completed, go to next step. If circuits are okay, go to step 31).
  34. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function then enter DTC P0300. If scan tool indicates TEST RAN AND PASSED, go to next step. If scan tool does not indicate TEST RAN AND PASSED, repeat step 2).
  35. If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time.
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