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Home >> GMC >> 1999 >> Forward Control 6.5 F, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures >> Basic Ignition System Checks >> Dis (3.4L) >> Electronic Ignition System Diagnosis (Secondary Ignition Check)

Electronic Ignition System Diagnosis (Secondary Ignition Check)

  1. Perform NO START DIAGNOSIS diagnosis. See NO START-ENGINE CRANKS OKAY (3.4L)  under NO START DIAGNOSIS. After performing no start diagnosis, go to next step.
  2. Install scan tool. Turn ignition on. If any Diagnostic Trouble Codes (DTCs) are present, diagnose DTCs. See appropriate SELF-DIAGNOSTICS article. If DTCs are not present, go to next step.
  3. Using scan tool, perform Fuel Injector Balance Test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Note cylinders with no engine speed or idle quality change. If any cylinders were noted, go to next step. If no cylinders were noted, go to step  17.
  4. If 2 companion cylinders were noted, go to step  10. If 2 companion cylinders were not noted, go to next step.
  5. Using DVOM, measure resistance of affected spark plug wire from end-to-end, and then from one end to ground. If spark plug wire is shorted to ground, or resistance is greater than 7000 ohms, go to step  22. If spark plug wire is not shorted to ground, or resistance is 7000 ohms or less, go to next step.
  6. Remove affected spark plug. If spark plug looks okay, go to next step. If spark plug does not look okay, go to step  23.
  7. Using DVOM, measure resistance of affected spark plug. If resistance is less than 10,000 ohms, go to next step. If resistance is 10,000 ohms or greater, go to step  23.
  8. Ground companion spark plug lead of affected cylinder. Install Spark Tester (J-26792). Crank engine and note spark. If spark jumps tester gap, go to FUEL SYSTEM PRESSURE TEST  under BASIC FUEL SYSTEM CHECKS (GASOLINE). If spark does not jump tester gap, go to next step.
  9. Ground affected spark plug lead. Install spark tester on companion cylinder of affected cylinder. Crank engine and note spark. If spark jumps tester gap, go to step  25. If spark does not jump tester gap, go to step  26.
  10. Ground one affected spark plug lead. Install spark tester on companion cylinder. Crank engine and note spark. If spark jumps tester gap, go to step  12. If spark does not jump tester gap, go to next step.
  11. Switch affected coil with another coil and perform Fuel Injector Balance Test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If fault follows affected coil, go to step  25. If fault does not follow affected coil, go to step  26.
  12. Reinstall all spark plugs and wires. Start engine and check for visible/audible arcing. If ignition system is arcing externally, go to step  27. If ignition system is not arcing externally, go to next step.
  13. Ground other affected spark plug lead. Install spark tester on companion cylinder. Crank engine and note spark. If spark jumps tester gap, go to next step. If spark does not jump tester gap, go to step  25.
  14. Using DVOM, measure resistance of affected spark plug wire from end-to-end, and then from one end to ground. If spark plug wire is shorted to ground, or resistance is greater than 7000 ohms, go to step  22. If spark plug wire is not shorted to ground, or resistance is 7000 ohms or less, go to next step.
  15. Remove affected spark plugs and check for wear, damage or fouling. If both spark plugs are okay, go to next step. If spark plugs are faulty, go to step  24.
  16. Using DVOM, measure resistance of affected spark plugs. If both spark plugs individually measure less than 10,000 ohms, go to FUEL SYSTEM PRESSURE TEST  under BASIC FUEL SYSTEM CHECKS (GASOLINE). If both spark plugs individually measure 10,000 ohms or greater, go to step  24.
  17. Install spark tester on one spark plug wire and ground companion cylinder. Note spark with engine idling. Repeat test for all spark plugs ensuring companion cylinder is grounded. If spark jumps tester gap on all cylinders, go to FUEL SYSTEM PRESSURE TEST  under BASIC FUEL SYSTEM CHECKS (GASOLINE). If spark does not jump tester gap, go to next step.
  18. Switch affected coil with another coil and repeat spark tester test on all 4 cylinders of switched coils. If fault follows affected coil, go to step  25. If fault does not follow affected coil, go to next step.
  19. Switch coils back to original location. Using DVOM, measure resistance of affected spark plug wire from end-to-end, and then from one end to ground. If either spark plug wire is shorted to ground, or resistance is greater than 7000 ohms, go to step  22. If either spark plug wire is not shorted to ground, or resistance is 7000 ohms or less, go to next step.
  20. Remove affected spark plugs and check for wear, damage or fouling. If both spark plugs are okay, go to next step. If spark plugs are faulty, go to step  24.
  21. Using DVOM, measure resistance of affected spark plugs. If both spark plugs individually measure less than 10,000 ohms, go to step  26. If both spark plugs individually measure 10,000 ohms or greater, go to step  24.
  22. Replace spark plug wire. After repairs, go to step  28.
  23. Replace spark plug. After repairs, go to step  28.
  24. Replace affected spark plug. After repairs, go to step  28.
  25. Replace affected coil. After repairs, go to step  28.
  26. Replace ICM. After repairs, go to step  28.
  27. Repair source of arcing. After repairs, go to next step.
  28. Operate vehicle within conditions in which problem occurred. If driveability problem is present, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. If driveability problem is not present, system is okay.
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