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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 151 (ENGINE CONTROL SYSTEM & ENGINE COMPONENT TESTS - 2.2L)FUEL SYSTEMSFUEL TANK LEAK TESTDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 GMC Sonoma and 2003 Chevrolet S10 Pickup. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article.
    2. CAUTION: Gasoline or gasoline vapors are highly flammable. A fire could occur if an ignition source is present. Never drain or store gasoline or diesel fuel in an open container, due to the possibility of fire or explosion. Have a dry chemical (Class "B") fire extinguisher nearby.
  2. Raise and support vehicle. Inspect fuel tank and fuel pipes for damage or external leaks. Did you find fuel leaking from the fuel tank? If yes, go to step  6. If no, go to next step.
  3. Turn ignition on, with engine off. Using scan tool, command fuel pump relay on. Inspect for fuel leaking from the fuel pipes. Did you find fuel leaking from the fuel pipes? If yes, go to step  7. If no, go to next step.
  4. Turn ignition off. Install Fuel Tank Cap Adapter (J-41415-40). Connect the Evaporative Emissions System Tester (J-41413-200) to fuel tank cap adapter. Turn ignition on, with engine off. Seal the EVAP system with scan tool. DO NOT exceed 15 in. H2O. Pressurize fuel tank using evaporative emissions system tester. Did fuel leak from the fuel tank? If yes, go to step  6. If no, go to next step.
  5. Maintain pressure in the fuel tank with the evaporative emissions system tester. The fuel tank may need to be partially lowered. Using an Ultrasonic Leak Detector (J-41416), test for leaks above the fuel level in the following locations: fuel tank, fill limiter vent valve, pressure relief valve and the rollover valves. Check the fuel sender housing and fuel sender seal. Check the FTP sensor seal, EVAP vapor pipes, fuel fill pipe, fuel fill hose, and fuel fill cap. Did you find and correct the condition? If yes, go to step  8. If no, go to DIAGNOSTIC AIDS .
  6. Replace fuel tank. See appropriate REMOVAL & INSTALLATION article. After replacing fuel tank, go to step  8.
  7. Replace the leaking fuel pipe. After repairs, go to next step.
  8. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. 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.