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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 (Cab & Chassis) >> 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 a Vacuum Gauge (J-44638) to the fuel system service port, located on right front side of the engine.
  2. Remove the air duct from the air cleaner assembly to the turbo inlet.
  3. Remove the generator for visibility of fuel supply lines.
  4. Prime the fuel manager until 10 psi is indicated on the vacuum gauge.
  5. Check for external fuel leaks between the fuel filter/heater assembly and the 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 the 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  23. 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 clamp the plug.
  9. Disconnect fuel return line at the engine.
  10. Install a hand-held vacuum pump on the fuel return pipe on the 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 the fuel system components on top of the engine for vacuum leaks. Apply at least 25 in. Hg to the fuel return pipe and wait more than one minute for the system to stabilize. Repeat 6 six 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  16.
  12. Reconnect the fuel supply line and the return line at the engine.
  13. Install a transparent hose between the Fuel Injection Control Module (FICM) outlet and fuel filter inlet, with a vertical loop to observe the incoming fuel for air bubbles. FICM is located on top front right of engine.
  14. Install generator.
  15. Prime the fuel system 30 times to remove the air from the fuel hoses. If engine does not start in the next step, go to step  23. Engine must be run for at least 10 minutes to allow the fuel system to stabilize and remove all air from the fuel system.
  16. Start engine.
  17. Observe the 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  28. If any air bubbles are entering the transparent hose with the incoming fuel, turn engine off and go to step  19.
  18. Check the fuel injection pump and the on-engine fuel suction system for air leakage.
    • Disconnect the fuel outlet hose from outlet pipe of the fuel filter assembly. See Figure.
    • Open the drain on the fuel filter assembly and drain the fuel into a suitable container.
    • Close the drain.
    • Install vacuum gauge on the outlet port of the fuel filter assembly.
    • Apply 15 in. Hg to the fuel pipe and observe the 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 fuel supply line fitting and fuel filter assembly.
    • Remove vacuum gauge from outlet port of the fuel filter assembly and install vacuum gauge to fuel outlet hose.
    • Remove the air intake pipe.
    • Remove supply hose from fuel injection pump and plug hose.
    • Apply 15 in. Hg and observe reading. If vacuum drops, repair leak between 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 fuel return pipe on fuel injection pump with a 5/16" rubber plug and clamp the plug.
    • Install vacuum gauge to fuel inlet pipe of the fuel injection pump.
    • Apply 20 in. Hg and observe vacuum hose. If vacuum drops, replace fuel injection pump, then go to step  28. If vacuum does not drop, replace fuel injection pump inlet supply hose, then go to step  28.
  19. Check the fuel sender for air leakage.
    • Remove front fuel tank.
    • Remove fuel sender from the fuel tank.
    • Remove strainer from fuel sender and plug the 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 the fuel sending unit and the chassis fuel line for damage and correct as necessary. If sealing surfaces are not damaged, replace fuel line between the chassis line and the fuel sending unit, then go to step  20. If vacuum does not hold, replace fuel sender. Reinstall fuel tank and go to step  20.
  20. Prime the fuel system 30 times or until fuel pressure is 10 psi to remove the air from the fuel system. Air will be forced out of the system within 2 minutes.
  21. Start and operate engine.
  22. Observe fuel 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  28. If any air bubbles are entering the transparent hose with the incoming fuel, stop the engine and go to step  8.
  23. Prime the fuel system 30 times or until fuel pressure is 10 psi to remove the air from the fuel system. Air will be forced out of the system within 2 minutes.
  24. Remove the hose from the fuel filter assembly outlet fitting and plug the hose.
  25. Verify that vacuum gauge is installed.
  26. Remove ignition 1 relay. Relay is located in underhood fuse/relay block.
  27. Crank engine 2-3 times in 15 second intervals and observe vacuum gauge. If vacuum gauge indicates 5 in. Hg or more, go to next step. If vacuum gauge indicates less than 5 in. Hg, replace fuel injection pump, then go to next step.
  28. Remove the transparent hose, if necessary and attach any disconnected components or fuel lines.
  29. Prime the fuel system 30 times to remove the air in the fuel hoses
  30. Clean any fuel spillage.
  31. Start engine. If engine starts and stalls, repeat step  29.
  32. Operate engine to check for fuel leakage.
  33. Verify that the customer's concern is corrected. If customer concern is not corrected, go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - 6.6L SIERRA & SILVERADO - DIESEL article.
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