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Ignition System (3.1L VIN M "W" Body)

  1. Disconnect tachometer wire (if equipped). A shorted tachometer or tachometer circuit will prevent vehicle from starting.
  2. Install scan tester. Check for stored PCM trouble codes. Scan TP sensor voltage. If TP sensor reading is greater than 2.5 volts, use diagnostic trouble Code 21 chart first. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below.
    • G - TESTS W/CODES - 3.1L
    • G - TESTS W/CODES - 3.4L
    • G - TESTS W/CODES - 3.8L
  3. Scan RPM while cranking engine. If RPM is displayed on scan tester, go to step 7). If RPM is not displayed, check for spark on 2 wires (2-4 or 4-6) using Spark Tester (ST-125). Check one wire at a time. Leave other wires connected to spark plugs while cranking.
  4. If spark occurs on both wires, go to next step. If no spark occurs on either wire, use diagnostic trouble Code 82. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below. If spark occurs on one wire only, go to step 6).
    • G - TESTS W/CODES - 3.1L
    • G - TESTS W/CODES - 3.4L
    • G - TESTS W/CODES - 3.8L
  5. Turn ignition off. Disconnect 6-wire ignition module connector. Turn ignition on. Monitor scanned RPM while momentarily touching RPM reference circuit wire (circuit No. 430) of ignition module harness connector with a test light connected to battery voltage. See Fig 1 . If RPM is indicated on scan tester, problem is faulty ignition module-to-harness connection or faulty ignition control module. If RPM is not indicated, problem is open or short to ground in RPM reference circuit or faulty PCM.
  6. If spark occurs on one wire only, check pair of wires for plug that did not spark. Each wire should measure 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 control module is faulty.
  7. Scan fuel pump signal (PPSW) during cranking. If voltage is not indicated, see appropriate diagnostic trouble Code 54 chart. If voltage is indicated, turn ignition off. Install fuel pressure gauge. Turn ignition on. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm2 ).
  8. If fuel pressure is not as specified, diagnose fuel system. If fuel pressure is okay, disconnect injector No. 1 or 6 harness connector. Turn ignition on, engine off. Using a test light connected to ground, probe test light on injector harness circuit No. 839 (Pink wire). See Fig 1 .
  9. If test light did not illuminate, check for open in circuit No. 839 (Pink wire). If test light illuminated, disconnect 10-pin injector harness connector. Install DVOM and set to 1 k/ohm position. Connect DVOM positive probe to injector harness terminal "D" (Pink wire) and touch DVOM negative probe to injector harness terminals "A", "B", "C", "F" and "G". Resistance should be less than 20 ohms.
  10. If resistance is not as specified, check injector harness circuit. If circuit is okay, replace faulty injector. If resistance is as specified, set DVOM to DC volts position. With DVOM positive probe connected to battery voltage, probe injector harness terminals "A", "B", "C", "H", "J" and "K" while cranking engine. DVOM should read/toggle from zero to 12 volts on each terminal.
  11. If reading is as specified, problem is not present at this point. If reading is not as specified, check for open injector circuit, faulty PCM connections or faulty PCM.
Fig 1: 3.1L (VIN M) MFI Ignition Sys. (Achieva, Grand Am & Skylark)
G94J34065Courtesy of GENERAL MOTORS CORP.
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