Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1995FORWARD CONTROL 4.3 Z, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - BASIC DIAGNOSTIC PROCEDURES - 4.3LC-4, BASIC IGNITION SYSTEM CHECKSENHANCED/HIGH VALUE IGNITION SYSTEM (OBD-II)IGNITION COIL POWER SOURCE
1995 GMC Forward Control 4.3 Z, Standard
Ignition Coil Power Source
1995 GMC Forward Control 4.3 Z, StandardSECTION Ignition Coil Power Source
- Turn ignition off. Disconnect ignition coil driver module connector. Turn ignition on. Using DVOM, check voltage at ignition coil driver module terminals "A" and "D". See Figure. Both terminals should read 10 volts or greater. If voltage is as specified on both terminals, go to next step. If voltage is 10 volts or less on either or both terminals, go to step 6).
- Place DVOM on AC scale. Connect DVOM to ignition coil module terminal "B" and ground. Crank engine. Voltage reading should be 1-4 volts. If voltage reading is as specified, go to next step. If voltage reading is not as specified, go to step 4).
- Connect test light to battery voltage and probe coil driver module connector terminal "C". See Figure. If test light illuminates, check for faulty ignition coil driver module connection or faulty ignition coil module. If test light does not illuminate, check for open ignition coil driver module ground.
- Turn ignition off. Disconnect Gray VCM-A harness connector. Check for continuity between VCM-A ignition control connector terminal and ignition driver module connector terminal "B". If continuity is present, go to next step. If continuity is not present, check for open IC circuit between VCM-A and ignition coil driver module.
- Connect test light to battery voltage and probe VCM-A ignition control harness terminal. If test light illuminates, check for grounded IC circuit between VCM-A and ignition coil driver module. If test light does not illuminate, check for faulty VCM-A connection or VCM-A.
- If voltage is less than 10 volts on both terminals, check for faulty ignition feed circuit to ignition coil, grounded external coil circuit or faulty ignition coil. If voltage is less than 10 volts on only one of the terminals, check circuit from affected terminal or check for faulty coil connection or faulty coil.
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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.