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 283 (ENGINE CONTROLS - TROUBLESHOOTING - NO CODES)SYMPTOMSPOOR FUEL ECONOMYFUEL SYSTEM
1999 GMC Forward Control 5.7 R, Automatic
Fuel System
1999 GMC Forward Control 5.7 R, AutomaticSECTION Fuel System
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
- Test the fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.6L DEVILLE & SEVILLE article.
- Test the fuel injectors. See FUEL INJECTOR COIL TEST , FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL or FUEL INJECTOR BALANCE TEST WITH TECH 2 under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.6L DEVILLE & SEVILLE article.
- Inspect for fuel in the pressure regulator.
- Inspect the minimum idle speed.
- Inspect for items that cause the engine to run rich.
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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.