Ignition System (3.4L "F" Body)
- Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
- Install scan tester. Check for stored ECM trouble codes. Scan TPS voltage. If TPS reading is greater than 2.5 volts, use Code 21 chart first. Scan RPM while cranking engine. If 3X RPM signal is displayed on scan tester, go to step 5). If RPM is not displayed, check for spark on each coil (1-4, 2-5 or 3-6) using Spark Tester (ST-125). Check one wire at a time. Ground the companion cylinder plug wire while cranking. Leave the other 4 wires connected to spark plugs. If a crisp Blue spark occurs on all wires, go to next step. If no spark occurs on either wire, go to Code 82 chart in appropriate TESTS W/CODES
article in the ENGINE PERFORMANCE Section. If spark occurs on one wire only, go to step 4).
- Turn ignition off. Disconnect 6-wire ignition module connector. Turn ignition on. Monitor scanned RPM while momentarily touching RPM reference circuit wire (circuit No. 647) of ignition module harness connector with a test light connected to battery voltage. If RPM is indicated on scan tester, problem is faulty ignition module-to-harness connection or faulty ignition module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty ECM.
- If spark occurs on one wire only, check pair of wires for plug that did not spark. Ensure each wire measures less than 30,000 ohms resistance. If wires are okay, switch coil assemblies. If problem moves with coil, replace faulty coil. If problem does not follow coil, ignition module is faulty.
- Scan fuel pump signal (PPSW) during cranking. If voltage is not indicated, see Code 54 chart in appropriate TESTS W/CODES
article in the ENGINE PERFORMANCE Section. If voltage is indicated, check fuel system pressure. See BASIC FUEL SYSTEM CHECKS. If fuel pressure is within specification, go to next step.
- Disconnect injector No. 1 or 2 harness connector. Turn ignition on. With test light connected to ground, probe Pink/Black wires of injector harness connectors. See Fig 1
. If light is not on, repair open in injector power supply wire.
- If test light is on, connect Injector Tester (J-32730-3C) to injector No. 1. Crank engine. Repeat test on remaining injectors. Test light should flash for each injector while engine is cranking. If test light flashes on all injectors, go to next step. If test light did not flash for all injectors, repair open in circuit that did not flash, check for faulty ECM connection on that circuit or replace faulty ECM.
- At this point, no problem has been isolated for not start condition. A damaged crankshaft reluctor ring may cause a crank but will not run condition.
Courtesy of GENERAL MOTORS CORP.