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Engine Controls - Basic Diagnostic Procedures: Diagnosis GMC Safari II

Testing & Diagnostics ~2353 words

VISUAL INSPECTION

Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see appropriate VACUUM DIAGRAMS article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Diagnosis

  1. Start engine and allow it to reach normal operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. If reading exceeds 1.25 psi (.09 kg/cm 2 ), exhaust system is restricted.
  2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as necessary.

NO START DIAGNOSIS

Note. For terminal and circuit identification, see appropriate wiring diagram in WIRING DIAGRAMS article.

  1. Definition No start is defined as engine cranks properly, but does not start. Engine may fire a few times.

General Inspection

  1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
  2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.
  1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
  2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.
  1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
  2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.
  1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
  2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

Ignition Relay Diagnosis

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
  2. Turn ignition off. Remove IGN relay from underhood electrical center. Using a test light connected to ground, probe IGN relay battery feed circuit at IGN relay connector. See appropriate wiring diagram in WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
  3. Turn ignition on with engine off. Using a test light connected to ground, probe IGN relay ignition feed circuit at IGN relay connector. See appropriate wiring diagram in WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 9 .
  4. Turn ignition off. Using DVOM, measure resistance between ground and IGN relay ground circuit at IGN relay connector. See appropriate wiring diagram in WIRING DIAGRAMS article. If resistance is less than 5 ohms, go to next step. If resistance is not as specified, go to step 10 .
  5. Using a fused jumper wire, jumper IGN relay battery feed circuit and IGN relay load circuit together at IGN relay connector. Using a test light connected to ground, probe both sides of the following fuses located in underhood electrical center: ENG I (10-amp) INJR A (15-amp) INJR B (15-amp) If test light illuminates at both sides of all fuses, go to next step. If test light does not illuminate at both sides of all fuses, go to step 11 .
  6. Check IGN relay for poor terminal connections. Repair as necessary. If connections are okay, go to next step.
  7. Replace IGN relay.
  8. Repair open in IGN relay battery feed circuit.
  9. Repair open in IGN relay ignition feed circuit.
  10. Repair open in IGN relay ground circuit.
  11. Repair open in IGN relay load circuit.

Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. In very cold temperatures, ensure oil is proper viscosity and not contaminated. Ensure glow plug system is operating properly.

INJECTOR CIRCUIT DIAGNOSIS

Note. This test only applies to vehicles equipped with a VCM.

FUEL PUMP FLOW TEST

  1. Remove fuse for fuel pump circuit. See appropriate wiring diagram in WIRING DIAGRAMS article. Disconnect fuel line at fuel pump outlet fitting. Install a hose at fuel pump outlet fitting and place hose in a container to collect fuel.
  2. Crank engine for 15 seconds. If fuel pump does not supply about a 1/2 pint of fuel in 15 seconds, go to «FUEL SYSTEM PRESSURE TEST»(ref-174-S32907151462000030800000) .

FUEL SYSTEM PRESSURE TEST

Note. For fuel pump circuit testing, see appropriate FUEL SYSTEM ELECTRICAL CIRCUIT under NO START DIAGNOSIS .

  1. Turn ignition off. Install tee adapter and pressure gauge at injection pump. Start engine and measure fuel pressure.
  2. If fuel pressure is not 4 psi (.28 kg/cm 2 ), check fuel lines and fuel tank sending unit for restriction. If fuel lines and sending unit are okay, replace fuel pump.

Ignition Coil Test (2.2L, 4.3L, 5.0L, 5.7L & 7.4L)

  1. Turn ignition off. Remove engine cover. Disconnect wiring from ignition coil and distributor lead.
  2. Using DVOM, check for continuity between coil primary terminal and exterior case of coil (ground). Replace ignition coil if continuity is present.
  3. Using DVOM, measure resistance between coil primary terminals. Replace ignition coil if resistance is not 0.1 ohm.
  4. Using DVOM, measure coil secondary resistance. Replace ignition coil if resistance is not 5000-25,000 ohms.
  5. Reconnect distributor lead and wiring to ignition coil. Install engine cover.

Ignition Coil Test (4.8L, 5.3L & 6.0L)

  1. Turn ignition off. Disconnect wiring from ignition coils.
  2. Using DVOM, measure resistance between ignition coil terminal "A" and ignition coil mounting bracket. See appropriate wiring diagram in WIRING DIAGRAMS article. Replace ignition coil if resistance is not 0-10,000 ohms.
  3. Using DVOM, measure coil secondary resistance. Replace ignition coil if resistance is not 3000-7000 ohms.

Electronic Ignition System Diagnosis (Primary Ignition Check)

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
  2. 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. Start engine. If a no start condition or hard-start condition is present, go to next step. If engine starts okay, go to step 5 .
  4. Turn ignition off. Disconnect Ignition Control Module (ICM) harness connector C2. Turn ignition on. Using DVOM measure voltage between ground and ignition battery voltage circuit at ICM harness connector C2. See appropriate wiring diagram in WIRING DIAGRAMS article. If voltage is less than 10 volts, go to next step. If voltage is 10 volts or greater, go to «NO START-ENGINE CRANKS OKAY (3.4L)»(ref-174-S18702155532000030800000) under NO START DIAGNOSIS.
  5. Drive vehicle and note driveability problems such as miss, stumble or hesitation. If driveability problem is present, go to «ELECTRONIC IGNITION SYSTEM DIAGNOSIS (SECONDARY IGNITION CHECK)»(ref-174-S30688258672000030800000) . If driveability problem is not present, go to next step.
  6. If any other driveability problem is present, go to appropriate TROUBLE SHOOTING - NO CODES article. If no other driveability problems are present, go to step 8 .
  7. Check ELEK IGN fuse (10-amp), located in underhood junction block. If fuse is open, repair short to ground in ignition battery voltage circuit between fuse and ICM. Replace fuse. If fuse is okay, check for open in ignition battery voltage circuit. See appropriate wiring diagram in WIRING DIAGRAMS article. Check for loose or corroded terminals and connections. Repair as necessary. After repairs, go to next step. If circuit, terminals and connections are okay, go to appropriate TROUBLE SHOOTING - NO CODES article.
  8. 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.

Electronic Ignition System Diagnosis (Secondary Ignition Check)

  1. Perform NO START DIAGNOSIS diagnosis. See «NO START-ENGINE CRANKS OKAY (3.4L)»(ref-174-S18702155532000030800000) 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»(ref-174-S32907151462000030800000) 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»(ref-174-S32907151462000030800000) 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»(ref-174-S32907151462000030800000) 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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