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 DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - BASIC DIAGNOSTIC PROCEDURESBASIC FUEL SYSTEM CHECKS (DIESEL ENGINES)FUEL PUMP FLOW TEST
1999 GMC Forward Control 5.7 R, Automatic
Fuel Pump Flow Test
1999 GMC Forward Control 5.7 R, AutomaticSECTION Fuel Pump Flow Test
- Remove fuse for fuel pump circuit. See appropriate wiring diagram in WIRING DIAGRAMS article. Disconnect fuel line at fuel pump outlet fitting. Install a hose at fuel pump outlet fitting and place hose in a container to collect fuel.
- Crank engine for 15 seconds. If fuel pump does not supply about a 1/2 pint of fuel in 15 seconds, go to FUEL SYSTEM PRESSURE TEST .
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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.