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Home >> Cadillac >> 2002 >> Escalade EXT >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Fuel System (Diesel) >> Fuel System Diagnosis - Pickup (6.6L) >> Fuel System Air Leak Check
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Fuel System Air Leak Check

  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. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
  4. Prime fuel manager until 10 psi is indicated on (J 44638).
  5. Check for external fuel leaks between fuel filter/heater assembly and fuel injection pump. If fuel is leaking externally, replace or repair leaking component. If no external fuel leaks are found, go to next step.
  6. Reprime fuel system until 10 psi is indicated on (J 44638). 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. See QUICK CONNECT FITTINGS (METAL COLLAR) under FUEL SYSTEMS in appropriate REMOVAL, OVERHAUL & INSTALLATION article.
  8. Cap off fuel supply pipe on engine with a 1/2" rubber plug and clamp.
  9. Disconnect fuel return line at engine. See QUICK CONNECT FITTINGS (METAL COLLAR) under FUEL SYSTEMS in appropriate REMOVAL, OVERHAUL & INSTALLATION article.
  10. Install Mityvac (J 23738-A) on fuel return pipe on engine.
  11. Check fuel system components on top of engine for vacuum leaks.
      NOTE: There is an orifice in fuel injection pump between fuel supply and fuel return systems. This will delay vacuum being pulled from fuel supply lines.
    1. Apply at least 25 inches of Hg of vacuum to fuel return pipe with (J 23738-A) and wait more than one minute for system to stabilize. Repeat this step 6 times.
    2. Observe (J 23738-A). If vacuum does not drop to less than 8 in. Hg within 10 minutes, go to next step. If vacuum drops to less than 8 in. Hg within 10 minutes, go to step  22.
  12. Reconnect fuel supply line and return line at engine.
  13. Disconnect chassis fuel line from short fuel line between fuel sender and chassis fuel line in front of fuel tank. See QUICK CONNECT FITTINGS (METAL COLLAR) under FUEL SYSTEMS in appropriate REMOVAL, OVERHAUL & INSTALLATION article.
  14. Plug chassis fuel line using a 1/2" rubber plug and clamp plug.
    15. NOTE: There is an orifice in fuel injection pump between fuel supply and fuel return systems. This will delay vacuum being pulled from fuel supply lines.
  15. Check fuel system components on top of engine for vacuum leaks.
    1. Apply at least 25 in. Hg of vacuum to fuel return pipe with (J 23738-A) and wait more than one minute for system to stabilize. Repeat this step 10 times.
    2. Observe (J 23738-A). If vacuum does not drop below 8 in. Hg within 10 minutes, go to next step. If vacuum does drop below 8 in. Hg within 10 minutes, inspect "O" ring sealing surfaces of 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 Fuel Injection Control Module (FICM) outlet and fuel filter inlet, with a vertical loop to observe incoming fuel for air bubbles.
  18. Install generator.
  19. Prime fuel system 30 times to remove air from fuel hoses.
    20. NOTE: Engine must be run for at least 10 minutes to allow fuel system to stabilize and remove all air from fuel system.
  20. Start and idle engine.
  21. Observe fuel in transparent hose for air bubbles. If there are no air bubbles of any kind entering transparent hose with incoming fuel, fuel suction system is okay. Go to step  29. If any air bubbles are entering transparent hose with incoming fuel, stop engine and go to step  23.
  22. Check fuel injection pump and on-engine fuel suction system for air leakage.
    1. Disconnect fuel outlet hose from outlet pipe of fuel filter assembly.
    2. Open drain on fuel filter assembly and drain fuel into a suitable container.
    3. Close drain.
    4. Install (J 23738-A) on outlet port of fuel filter assembly.
    5. Apply 15 in. Hg of vacuum to fuel pipe and observe (J 23738-A). If vacuum does not drop, connect fuel supply line at engine and go to step  F. If vacuum drops, repair air leak between fuel supply line fitting and fuel filter assembly.
    6. Remove (J 23738-A) from outlet port of fuel filter assembly and install (J 23738-A) to fuel outlet hose.
    7. Remove air intake pipe.
    8. Remove supply hose from fuel injection pump and plug hose.
    9. Apply 15 in. Hg of vacuum 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 step  J.
    10. Disconnect fuel injection pump return hose.
    11. Cap off fuel return pipe on fuel injection pump with a 1/2" rubber plug, and clamp plug.
    12. Install (J 23738-A) to fuel inlet pipe of fuel injection pump.
    13. Apply 20 in. Hg of vacuum and observe (J 23738-A). 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.
    1. Remove front fuel tank.
    2. Remove fuel sender from fuel tank.
    3. Remove strainer from fuel sender and plug bottom end of pickup tube.
    4. Apply 15 in. Hg of vacuum to upper end of pickup tube and observe (J 23738-A). If vacuum holds, inspect "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 chassis line and fuel sending unit, then go to step  29. If vacuum does not hold, replace fuel sender. Reinstall fuel tank and 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 system within 2 minutes.
  25. Remove hose from fuel filter assembly outlet fitting and plug hose.
  26. Verify (J 44638) is installed.
  27. Remove Ignition 1 relay.
  28. Crank engine 2-3 times in 15 second intervals and observe (J 44638). If (J 44638) indicates 5 in. Hg of vacuum or more, go to step  6. If (J 44638) indicates less than 5 in. Hg of vacuum, replace fuel injection pump, then go to next step.
  29. Remove transparent hose if necessary and attach any disconnected components or fuel lines.
  30. Prime fuel system 30 times to remove air in fuel hoses.
  31. Clean any fuel spillage.
  32. Start engine. If engine starts and stalls, repeat step  30.
  33. Run engine to check for fuel leakage.
  34. Verify customer concern is corrected. If customer concern is not corrected, go to SYMPTOM DIAGNOSIS under SYMPTOMS (DIESEL) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
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