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 261 (ENGINE CONTROLS TROUBLESHOOTING - NO CODES - 3.1L)SYMPTOMSPOOR FUEL ECONOMYADDITIONAL CHECKS
1999 GMC Forward Control 5.7 R, Automatic
Additional Checks
1999 GMC Forward Control 5.7 R, AutomaticSECTION Additional Checks
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
Check the exhaust system for any possible restrictions.
- See EXHAUST RESTRICTION under EXHAUST SYSTEM CHECK under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
- Check exhaust system for damaged or collapsed pipes.
- Check mufflers for heat distress or possible internal failure.
- For possible plugged catalytic converter.
- Check for proper Torque Converter Clutch (TCC) operation. Check the Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in TRANSMISSIONS.
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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.