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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 221 (Engine Controls - Basic Diagnostic Procedures - 6.6L Diesel) >> Fuel Systems >> Fuel System Diagnosis (Pickup) >> Fuel System Air Leak Check

Fuel System Air Leak Check

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Install Vacuum Gauge (J-44638) to fuel system service port on right front side of engine.
  2. Remove air duct from air cleaner assembly to turbo inlet.
  3. Remove generator for visibility of fuel supply lines.
  4. Prime fuel manager until 10 psi is indicated on vacuum gauge.
  5. Check for external fuel leaks between fuel filter/heater assembly and fuel injection pump. See Figure. If fuel is leaking externally, replace or repair the leaking component. If no external fuel leaks are found, go to next step.
  6. Reprime fuel system until 10 psi is indicated on the vacuum gauge. If fuel pressure drops from 10 psi to 2 psi in less than one minute, go to step  24. If fuel pressure drops from 10 psi to 2 psi in more than one minute, go to next step.
  7. Disconnect fuel supply line at engine.
  8. Cap off the fuel supply pipe on the engine with a 1/2" rubber plug and hose clamp.
  9. Disconnect fuel return line at engine.
  10. Install a hand-held vacuum pump on fuel return pipe on engine.
    11. NOTE: There is an orifice in the fuel injection pump between the fuel supply and fuel return systems. This will delay the vacuum being pulled from the fuel supply lines.
  11. Check fuel system components on top of the engine for vacuum leaks. Apply at least 25 in. Hg to fuel return pipe with the hand-held vacuum pump and wait more than one minute for the system to stabilize. Repeat this step 6 times. Observe vacuum gauge. If vacuum does not drop below 8 in. Hg within 10 minutes, go to next step. If vacuum drops below 8 in. Hg within 10 minutes, go to step  22.
  12. Reconnect fuel supply line and return line at engine. See Figure.
  13. Disconnect the chassis fuel line from the short fuel line between the fuel sender and chassis fuel line in front of the fuel tank.
  14. Plug the chassis fuel line using a 1/2" rubber plug and clamp the plug.
  15. Check the fuel system components on top of the engine for vacuum leaks.
    • Apply at least 25 in. Hg to fuel return pipe and wait more than one minute for the system to stabilize. Repeat 10 times.
    • Observe vacuum gauge. If vacuum does not drop below 8 in. Hg within 10 minutes, go to next step. If vacuum drops below 8 in. Hg within 10 minutes, inspect the "O" ring sealing surfaces of the engine fuel supply line for damage and correct as necessary. If sealing surfaces are not damaged, replace chassis fuel lines and go to step  29.
  16. Reconnect fuel line at fuel tank and fuel return line at engine.
  17. Install a transparent hose between the Fuel Injection Control Module (FICM) outlet and the fuel filter inlet, with a vertical loop to observe the incoming fuel for air bubbles. FICM is located on top right front of engine.
  18. Install generator.
  19. Prime fuel system 30 times to remove the air in the fuel system.
    20. NOTE: The engine must be run for at least 10 minutes to allow the fuel system to stabilize and remove all air from the fuel system.
  20. Start and operate engine at idle.
  21. Observe fuel in the transparent hose for air bubbles. If there are no air bubbles of any kind entering the transparent hose with the incoming fuel, the fuel suction system is okay. Go to step  29. If any air bubbles are entering the transparent hose with the incoming fuel, turn engine off and go to step  23.
  22. Check fuel injection pump and on-engine fuel suction system for air leakage.
    • Disconnect the fuel outlet hose from the outlet pipe of the fuel filter assembly.
    • Open drain on the fuel filter assembly and drain fuel into a suitable container.
    • Close the drain.
    • Install hand-held vacuum pump on outlet port of the fuel filter assembly.
    • Apply 15 in. Hg of vacuum to the fuel pipe and observe vacuum gauge. If vacuum does not drop, connect the fuel supply line at the engine and go to next step. If vacuum drops, repair air leak between the fuel supply line fitting and fuel filter assembly.
    • Install hand-held vacuum pump to fuel outlet hose from the fuel filter assembly.
    • Remove air intake pipe.
    • Remove supply hose from the fuel injection pump and plug the hose.
    • Apply 15 in. Hg of vacuum and observe the reading. If the vacuum drops, repair the leak between the fuel filter assembly outlet and fuel injection pump inlet. If vacuum does not drop, go to next step.
    • Disconnect fuel injection pump return hose.
    • Cap off the fuel return pipe on the fuel injection pump with a 1/2" rubber plug and clamp the plug.
    • Install hand-held vacuum pump to fuel inlet pipe of the fuel injection pump.
    • Apply 20 in. Hg and observe vacuum gauge. If vacuum drops, replace fuel injection pump, then go to step  29. If vacuum does not drop, replace fuel injection pump inlet supply hose, then go to step  29.
  23. Check fuel sender for air leakage.
    • Remove fuel tank.
    • Remove fuel sender from fuel tank.
    • Remove strainer from fuel sender and plug bottom end of the pickup tube.
    • Apply 15 in. Hg to the upper end of the pickup tube and observe vacuum gauge. If vacuum holds, inspect the "O" ring sealing surfaces of fuel sending unit and chassis fuel line for damage and correct as necessary. If sealing surfaces are not damaged, replace fuel line between the chassis line and fuel sending unit, then go to step  29. If vacuum does not hold replace fuel sender, reinstall fuel tank, then go to step  29.
  24. Prime fuel system 30 times or until fuel pressure is 10 psi to remove air from fuel system. Air will be forced out of the system within 2 minutes.
  25. Remove hose from fuel filter assembly outlet fitting and plug hose.
  26. Verify that vacuum gauge is installed.
  27. Remove ignition 1 relay. Relay is located in underhood fuse/relay block.
  28. Crank engine 2-3 times in 15 second intervals and observe vacuum gauge. If vacuum gauge indicates 5 in. Hg or more, go to step  6. If vacuum gauge indicates less than 5 in. Hg, replace fuel injection pump. After repairs, go to next step.
  29. Remove the transparent hose, if necessary and attach any disconnected components or fuel lines.
  30. Prime fuel system 30 times to remove air in the fuel hoses
  31. Clean any fuel spillage.
  32. Start engine. If engine starts and stalls, repeat step  30.
  33. Operate engine to check for fuel leakage.
  34. Verify that the customer's concern is corrected. If customer's concern is not corrected, go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - 6.6L SIERRA & SILVERADO - DIESEL article.
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