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 MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 284 (ENGINE CONTROLS - TROUBLE SHOOTING - NO CODES)SYMPTOMSENGINE BACKFIRESIGNITION SYSTEM
1999 GMC Forward Control 5.7 R, Automatic
Ignition System
1999 GMC Forward Control 5.7 R, AutomaticSECTION Ignition System
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
- Inspect for proper ignition voltage output with Spark Tester (J 26792).
- Remove spark plugs and inspect for the following:
- Wet Plugs
- Cracks
- Wear
- Improper Gap
- Burned Electrodes
- Heavy Deposits
- An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gauge gap tool.
- Determine the cause of the fouling before replacing the spark plugs.
- Visually and physically inspect secondary ignition for the following:
- Ignition wires arcing to ground.
- Ignition coils arcing to ground.
- Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water.
- Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use DTC P0300 for diagnosis. See DTC P0300: ENGINE MISFIRE DETECTED in SELF-DIAGNOSTICS - 5.7L CORVETTE article.
- Inspect for loose ignition coil grounds.
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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.