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 150 (ENGINE CONTROL SYSTEM - TROUBLE SHOOTING - NO CODES)SYMPTOM DIAGNOSISDETONATION/SPARK KNOCKFUEL SYSTEM CHECKS
1999 GMC Forward Control 5.7 R, Automatic
Fuel System Checks
1999 GMC Forward Control 5.7 R, AutomaticSECTION Fuel System Checks
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
- Check to determine if a lean system causes the condition. Drive vehicle at the speed of the complaint. Monitoring the Fuel Trim will help identify the problem. If the system is lean, the Long Term Fuel Trim will be more than 20 percent.
- Check the fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
- Check fuel injectors. Perform Fuel Injector Coil Test procedure and the Fuel Injector Balance Test procedure. See FUEL INJECTOR COIL TEST - ENGINE COOLANT TEMPERATURE BETWEEN 50-95°F (10-35°C) and FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
- Check for inferior quality fuel and the proper octane rating. See ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article. Fill fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Road test vehicle and re-evaluate vehicle performance.
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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.