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 263 (ENGINE CONTROLS - SYSTEM TESTING & ENGINE COMPONENT TESTS - 3.1L)FUEL SYSTEMSFUEL INJECTOR COIL TESTDIAGNOSTIC PROCEDURE
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Procedure
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedure
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.
- Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. After performing diagnostic system check - engine controls, go to next step.
- Using scan tool, check Engine Coolant Temperature (ECT) sensor value. Is the ECT sensor value 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4.
- Disconnect fuel injector harness connector. Using a DVOM, measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way harness connector. See Fig 1. Do any of the fuel injectors display a resistance outside 11-14 ohms? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
- Disconnect the fuel injector multi-way harness connector. Using a DVOM, measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way harness connector. See Fig 1. Record each fuel injector value. Subtract the lowest resistance value from the highest resistance value. Is the difference equal to, or less than 3 ohms? If yes, go to FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL or FUEL INJECTOR BALANCE TEST WITH TECH 2 . If no, go to next step.
- Add all fuel injector resistance values to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors, to obtain an average resistance value. Subtract the lowest and the highest individual fuel injector resistance values from the average resistance value. Replace the fuel injector that displays the greatest resistance difference, above or below the average. After repair, go to step 7.
- Replace the fuel injector or fuel injectors that are out of the 11-14 ohms range. After repair, go to next step.
- Operate system to verify repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step 2.
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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.