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HOMESERVICE MANUALSGMC1995RALLY G2500, 4.3 ZREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - BASIC DIAGNOSTIC PROCEDURES - 4.3LA-3, NO-START DIAGNOSISNO START - ENGINE CRANKS OKAY (ENHANCED/HIGH VALUE IGNITION SYSTEM)IGNITION SYSTEM
1995 GMC Rally G2500, 4.3 Z

Ignition System

1995 GMC Rally G2500, 4.3 ZSECTION Ignition System
  1. Check if Code P1221 is stored. If code is present, diagnose code first. Check TP sensor voltage. If TP sensor voltage is greater than 2.5 volts at closed throttle, see Code P0118. Check ECT sensor reading. If ECT sensor reading is -30°C, see Code P0118. See TESTS W/CODES - 4.3L article.
  2. Turn ignition off for 10 seconds. Turn ignition on. Listen for fuel pump operation. Fuel pump should operate for 2 seconds. If fuel pump operates, go to next step. If fuel pump does not operate, check fuel pump relay and circuit. See the appropriate SYSTEM/COMPONENT TESTS - 4.3L article.
  3. Disconnect injector connector at intake manifold. Connect Injector Test Light (J 34730) to wiring harness connector. Crank engine. If injector test light flashes, go to next step. If injector test light does not flash or stays on steady, go to step 6).
  4. Disconnect one spark plug wire. Install Spark Tester (ST-125). Crank engine and check for spark. If spark is present, go to next step. If spark is not present, proceed to the C-4, BASIC IGNITION SYSTEM CHECKS .
  5. Reconnect spark plug wire. Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Connect Fuel Pressure Gauge (J 34730-1). Turn ignition on. Fuel pressure should be 55-61 psi (3.9-4.3 kg/cm2 ) when fuel pump stops. Pressure should hold steady. If fuel pressure is as specified and holds steady, check injectors. See SYSTEM/COMPONENT TESTS - 4.3L article. If fuel pressure is not as specified, go to A-7, BASIC FUEL SYSTEM CHECKS .
  6. If injector test light does not illuminate, go to next step. If injector test light stayed on steady, check for short to ground in injector circuit. See Fig 1. If circuit is okay, check injector resistance. Injector resistance should be greater than 1.3 ohms. If resistance is as specified, replace VCM-A. If resistance is not as specified, replace faulty injector.
    Fig 1: Enhanced/High Value Ignition & Injector Circuits (4.3L CPI "S" & "T" Series A/T & M/T With VCM-A)
    G95F27354Courtesy of GENERAL MOTORS CORP.
  7. Turn ignition off. Disconnect coil high voltage wire. Disconnect3-pin crank sensor harness connector. Turn ignition on. Using test light connected to battery, momentarily touch test light to Yellow wire crank sensor harness connector terminal. If injector test light flashed, check for faulty crank sensor harness connection or faulty crank sensor. If injector test light does not flash, go to next step.
  8. Turn ignition off. Check for open or grounded Yellow wire to crank sensor or faulty VCM-A connector. If wire or connector is okay, remove injector test light.
  9. Turn ignition on. Using test light connected to ground, probe engine harness connector. If test light illuminates on one of the terminals, go to next step. If test light illuminates on both terminals, repair short to voltage in Dark Blue wire between injector and VCM-A. If test light does not illuminate on either terminal, repair open between ignition coil (Driver module) Pink wire to VCM-A.
  10. Turn ignition off. Reconnect injector connector. Disconnect Red VCM-A connector. Turn ignition on. Using test light connected to ground, probe VCM-A terminal No. RE3. If test light illuminates, check for faulty VCM-A connector or faulty VCM-A. If test light does not illuminate, check for faulty VCM-A connector or open in circuit.
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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.