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Home >> GMC >> 1998 >> Forward Control 7.4 B >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing - 4.3L >> Fuel System >> Fuel Control >> Fuel Injector Circuit Diagnosis
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Fuel Injector Circuit Diagnosis

  1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES article.
  2. Turn ignition switch to LOCK position. Disconnect fuel injector harness connectors. Using a test light connected to ground, probe appropriate injector ignition feed circuit at injector harness connector. Turn ignition switch to RUN position. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
  3. Connect Fuel Injector Test Light (J-34730-350) to fuel injector harness connectors one at a time. Crank engine while observing test light. If test light does not flash at each injector, go to next step. If test light flashes at each injector, perform inject coil test. See INJECTOR COIL TEST.
  4. If fuel injector test light illuminates constantly while engine is being cranked, go to next step. If fuel injector test light does not illuminate constantly while engine is being cranked, go to step 6).
  5. Install fuel injector test light on affected circuit. Turn ignition switch to LOCK position. Disconnect PCM/VCM harness connectors. Turn ignition switch to RUN position. If test light illuminates, go to step 8). If test light does not illuminate, go to step 11).
  6. Check injector control circuit for open or short to voltage between PCM and injector harness connectors. If open or short exists, go to next step. If open or short does not exist, go to step 9).
  7. Repair open or short to voltage in injector control circuit between PCM and injector harness connectors. After repairs are complete, go to step 12).
  8. Repair short to ground in injector control circuit, between PCM and injector harness connectors. After repairs, go to step 12).
  9. Check PCM/VCM harness connectors for poor connections. If poor connection exists, go to next step. If poor connection does not exist, go to step 11).
  10. Repair connections as necessary and go to step 12).
  11. Replace PCM/VCM and go to next step.
  12. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start and continue to run, go to step 2).
  13. Let engine idle until normal operating temperature is obtained. Retrieve DTCs. If no DTCs are present, system is okay at this time. If any DTCs are present, perform appropriate DTC test. See TESTS W/CODES article.
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