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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 3 (Engine Controls - Basic Testing) >> A-3, No-Start Diagnosis >> No Start - Engine Cranks Okay (3.8L With C(3)I) >> Ignition System (3.8L)

Ignition System (3.8L)

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  1. Ensure TPS scans less than 2.5 volts. If not, see Code 21 chart in appropriate BASIC TESTING article in this section. Check for stored trouble codes. See appropriate BASIC TESTING article in this section. If engine has not been started for at least 8 hours, MAT sensor scan temperature should be close to CTS scan temperature. Disconnect cam sensor and attempt to start engine. If engine starts, see Code 41 chart in appropriate BASIC TESTING article in this section.
  2. Reconnect cam sensor connector. Compare scanned CTS temperature with actual coolant temperature. If they are not close, replace coolant sensor. Depress accelerator pedal approximately 25 percent. Attempt to start engine. If engine does not start, go to next step. If engine starts, check IAC counts on scan tester. Check for stored Code 35. Check for blocked IAC passages.
  3. Disconnect all injector connectors and install injector test light in each injector harness connector. All lights should be off and should blink as engine is cranked. If any injector lights are on, go to step 6). If lights do not blink at all while cranking, go to step 7). If all lights are off and they blink as engine is cranked, check for adequate spark using Spark Tester (ST-125). Check for spark on plug wires No. 1, 3 and 5 (one at a time). Leave matching plug wire connected while checking for spark. If spark jumped tester on all plug wires, check for fouled spark plugs or for fuel system as cause of no start. See BASIC FUEL SYSTEM CHECKS (GASOLINE) . If spark did not occur on any plug wire, ignition module connection is poor or ignition module is faulty.
  4. If spark did not jump tester on all plug wires, verify that plug wire resistance is less than 30,000 ohms. Verify that ignition coils secondary resistance is 5000-6500 ohms at room temperature. Replace as necessary. If wires and coils are okay, remove coil that did not fire. Verify primary resistance of .3-.5 ohm. Replace coil if necessary. If coil is okay, connect a test light across ignition module terminals for problem coil.
  5. Crank engine. If test light flashes, check for poor coil to module connections. If connections are okay, replace faulty coil. If test light does not flash, replace ignition module.
  6. Turn ignition off. Disconnect PCM Black C-D connector. Turn ignition on. If all lights are now off, replace PCM. If any lights are still on, repair short to ground in that injector drive circuit.
  7. Check ignition module power supply (20-amp INJ fuse and circuit). Repair as necessary. Disconnect fuel injector connector. Turn ignition on. With a test light connected to ground, check for battery voltage on Pink/Black wire of injector harness. If test light is on, go to next step. If test light is off, check injector harness between injector connectors and 20-amp INJ fuse. If fuse is blown, repair short to ground and replace fuse. If fuse is okay, check power supply to fuse and circuit between fuse and the injector harness connector.
  8. Turn ignition off. Disconnect ignition module connector. Turn ignition on. Install injector test light in any injector harness connector. Connect test light to battery voltage, and repeatedly touch terminal "D" of ignition module harness connector. See Fig 1. Injector test light should flash each time test light is touched to terminal "D". If injector test light flashes, go to step 10).
    Fig 1: 3.8L PFI Ignition System
    G92E21786Courtesy of GENERAL MOTORS CORP.
  9. If injector test light does not flash, check injector drive circuit between PCM and injector harness connector for open or short to voltage. Repair as necessary. If injector drive circuit is okay, check for open, short to ground or short to voltage on fuel control circuit No. 430. If circuit is okay, problem is faulty connection at PCM fuel control terminal or faulty PCM.
  10. Turn ignition off. Using proper jumper adaptor from Adaptor Kit (J 35616), connect a fused jumper between ignition module harness connector terminal "N" and battery voltage. Connect a second jumper between ignition module harness connector terminals "M" and ground. Connect DVOM between ignition module harness connector terminal "H" and battery voltage. Observe voltmeter while cranking engine. Voltmeter should read approximately 1.7 volts.
  11. If voltage is high, check circuit No. 646 for open or short to ground. If open or short to ground is not present, replace faulty crank sensor. If voltage is low, check circuit No. 646 for an open or short to voltage, circuit No. 645 for an open and circuit No. 644 for an open or short to ground. If all circuits are okay, replace faulty crank sensor.
  12. If voltage is approximately 1.7 volts, move DVOM lead from terminal "H" to terminal "G". Crank engine and once again monitor voltage. Voltmeter should read about 5.5 volts. If voltage is correct, go to next step. If voltage is less than 5.5 volts, check for open or short to voltage in circuit No. 643. If voltage is greater than 5.5 volts, check for a short to ground on circuit No. 643. If no problem is found, crank sensor is faulty.
  13. If voltage is close to 5.5 volts, turn ignition on. Probe ignition module harness connector terminals "P" with a DVOM connected to ground. If battery voltage is not present, repair open in ignition module power supply circuit. If battery voltage is present, problem is poor ignition module connections or faulty ignition module.
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