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 DIAGNOSISSURGES/CHUGGLESFUEL 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.
- Determine if a rich or lean system can cause the condition. Drive the vehicle at the speed of the complaint. Monitoring the Fuel Trim may help identify the problem.
- Lean
The Long Term Fuel Trim will be more than 20 percent. - Rich
The Long Term Fuel Trim will be less than -20 percent.
- Lean
- Check the fuel injectors. Perform the following procedures:
- Fuel Injector Coil Test. See FUEL INJECTOR COIL TEST - ENGINE COOLANT TEMPERATURE BETWEEN 50-95°F (10-35°C) or FUEL INJECTOR COIL TEST - ENGINE COOLANT TEMPERATURE OUTSIDE 50-95°F (10-35°C) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
- Fuel Injector Balance Test. See FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
- Check the fuel pressure while the condition exists. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
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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.