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Home >> GMC >> 2000 >> Jimmy 2D Utility, RWD, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P0300-P0306: Engine Misfire Detected >> Diagnostic Procedures

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. Using scan tool, check if any other DTCs are set. Diagnose affected DTC(s). If no other DTCs are set, go to next step.
  3. Start engine. Using scan tool, monitor misfire counters in MISFIRE DATA LIST with a load on engine. If misfire counter is increasing, go to step  5. If misfire counter is not increasing, go to next step.
  4. Turn engine off. Using a spray bottle filled with water, wet down secondary ignition system. Start engine. Monitor misfire counters with a load on engine. If scan tool indicates a misfire is present, diagnose ignition system. If no misfire is present, go to step  16.
  5. If misfire is random on all cylinders, go to step  10. If misfire is not random, go to next step.
  6. If misfire is consistent on a specific cylinder, go to next step.
  7. Turn ignition off. Connect Spark Tester (J-26792) to ignition wires of cylinders indicating a misfire. Start engine. If tester indicates spark is consistent on all tested ignition wires, go to next step. If spark is not consistent, diagnose ignition system.
  8. Remove spark plug from cylinder that indicate a misfire and check spark plug condition. If a problem is found, go to step  15. If no problem is found, go to next step.
  9. Reinstall spark plug(s). Start engine. Using scan tool, monitor misfire counters in the misfire data list. If misfire moved to another cylinder, go to step  13. If misfire did not move to another cylinder, go to step  11.
  10. Perform fuel system diagnostic. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. After repairs, go to step  17. If no problems were found, go to step  14.
  11. Connect Injector Test Light (J-34730-375) to cylinders that indicated a misfire. Crank engine for about 10 seconds. If test light flashed on all tested circuits while cranking engine, go to next step. If test light did not flash on all tested circuits while cranking engine, diagnose fuel injector circuit. See INJECTOR CIRCUIT DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  12. Perform fuel injector balance test. See FUEL SYSTEM (GASOLINE) in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. If no problem is found, go to step  17.
  13. Replace spark plugs. After replacing sparks plugs, go to step  17.
  14. Check for contaminated fuel, fouled or damaged spark plugs, faulty ignition coil or connections. Check for damaged distributor cap, leaking EGR valve, restricted exhaust or poor VCM grounds. Repair as necessary. After repairs, go to step  17.
  15. Check for engine mechanical problems. Repair as necessary. After repairs, go to step  17. If no problems were found, see DIAGNOSTIC AIDS .
  16. Perform CKP variation learn procedure. To perform learn procedure, enable CRANKSHAFT POSITION SYSTEM VARIATION LEARN PROCEDURE on scan tool. Apply and hold service brake. Slowly raise engine speed to 4000 RPM. Immediately release throttle when engine speed decreases. Turn ignition off for 15 seconds after learn procedure is completed successfully. After performing learn procedure, go to next step.
  17. Using scan tool, select DTC and clear DTC. Warm engine to normal operating temperature. Select DTC and Specific DTC function. Enter DTC and operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic passed, go to next step. If scan tool does not indicate that this diagnostic passed, go to step  2.
  18. Check for any additional undiagnosed DTCs. Diagnose affected DTC(s). If no other DTC(s) are set, system is okay.
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