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HOMESERVICE MANUALSBUICK1990REGAL CUSTOM, 3.8 L, 4T60/ME9REPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - BASIC TESTINGNO START DIAGNOSISNO START - ENGINE CRANKS OKAY (PFI WITH C(3)I)IGNITION SYSTEM (3.8L)
1990 Buick Regal Custom, 3.8 L, 4T60/ME9

Ignition System (3.8L)

1990 Buick Regal Custom, 3.8 L, 4T60/ME9SECTION Ignition System (3.8L)
  1. Ensure that fuel quantity and quality is okay. Turn ignition on with throttle closed. Service engine soon light should be ON. (If not see SERVICE ENGINE SOON LIGHT INOPERATIVE). Connect scan tool according to manufacturer's instructions. TPS should scan less than 2.5 volts (2500 ma). (If not see CODE 21 chart in appropriate TESTS W/CODES article.) Disconnect cam sensor and crank engine. If it starts, see CODE 41 chart in appropriate TESTS W/CODES article. If not, continue. On a cold engine (not run for 8 hours) MAT should be close to CTS value. If not, compare scan value of coolant temperature sensor to actual coolant temperature. Values should be close. If not, replace coolant temperature sensor.
  2. Reconnect cam sensor. Depress throttle to approximately 1/4 position. attempt to start engine. If engine starts, check Idle Air Control system. If engine does not start, disconnect all injector connectors and install injector test light J 34730-2 or equivalent in each injector harness connector. Test lights should be off. If test lights are on, go to step 3. If test lights are off, Crank engine and observe if test lights blink. If test lights do not blink, go to step 3. If test lights blink, go to step 4).
  3. If light is glowing steadily, disconnect ECM gray connector. If light does not turn off, repair short to ground in injector wiring. If light turns off, ECM is faulty. If test light is off, check INJ fuse. If fuse is not okay, repair short to ground in CKT 839 and replace fuse. If fuse is okay, remove injector test light. Probe injector harness CKT 839 at each injector terminal "A" with a test light to ground. If test light is off, check circuit from ignition feed for an open circuit. If test light is on, go to step 6).
    NOTE: If an injector driver circuit has been continuously grounded check oil for fuel contamination and exhaust system restriction.
  4. Turn ignition off, install fuel pressure gauge and note pressure after ignition is turned ON for 2 seconds, pressure should be 40-47 psi (280-325 kpa) and holding. If no pressure is read, go to FUEL SYSTEM below. If pressure is incorrect, go to FUEL PRESSURE CHECK (PFI). If pressure is correct, go to step 4).
  5. Check for spark with spark tester (ST-125) J 26792, or equivalent on plug wires 1, 3 & 5 one at a time while cranking, with remaining plug wires still connected. If there is spark on all wires, check for fouled spark plugs. Clean or replace as necessary, then check Idle Air Control system. No spark on all wires, check for faulty ignition module connection or module. If there is no spark on one or more wires, check the following:
    • Verify that plug wire resistance is less than 30k ohms. If resistance is not as specified, replace wire.
    • Verify coil secondary resistance is 5000-6500 ohms at approximately. 70°F. If resistance is not as specified, replace coil.
    • Remove coil for cylinder(s) that did not fire. Verify coil primary resistance is .3 -.5 ohms. If resistance is not as specified, replace coil.
    • Connect a test light between ignition module terminals for problem coil. The test light should blink while cranking engine. If test light does not blink, the ignition module is faulty. If test light does blink, the ignition coil connection or coil is faulty.
  6. Turn ignition off. Disconnect 14 pin harness connector from ignition module. Install an injector test light in any injector harness connector. Turn ignition ON, connect a test light to 12 volts and repeatedly touch to ignition module harness terminal "D". Injector test light should blink. If test light blinks, go to step 7). If test light does not blink, Check injector driver circuit from ECM for an open or short to voltage. If circuit is okay, check CKT 430 for open or short to ground or to voltage. If circuit is ok, check for poor connection at ECM terminal "G9" or faulty ECM. If circuit is not okay, repair injector driver circuit.
  7. Turn ignition off. Using appropriate jumper adaptor from connector test adaptor kit J 35616, connect a fused jumper between ignition module harness connector terminal "N" (CKT 644) and B+. Connect a second jumper between ignition module harness connector terminal "M" (CKT 645) and ground. Connect test light between ignition module harness connector terminal "H" (CKT 646) and B+. Test light should flash ON and OFF as starter is bumped. If test light does flash, go to step 8). If test light is on all the time, check CKT 646 for a short to ground. If circuit is okay, check for a faulty crank sensor. If test light is never on, check CKT 646 for an open or short to voltage, CKT 645 for an open, and CKT 644 for an open or short to ground. If circuit is okay, check for a faulty crank sensor.
  8. Connect test light between ignition module harness connector terminal "G" (CKT 643) and B+. Observe test light while repeatedly bumping starter. Test light should flicker as starter is bumped. If test light flickers, go to step 9). If test light is on all the time, check CKT 643 for a short to ground. If okay, check for a faulty crank sensor. If test light is never on, Check CKT 643 for an open or short to voltage. If okay, it's a faulty crank sensor.
  9. Turn ignition on. Probe ignition module harness connector terminal "P" (CKT 839) with a test light to ground. If test light is on, check for poor connections at ignition module or faulty ignition module. If test light is not on, repair open CKT 839 to ignition module.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.