GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Bulletins 🢒 SMU - Fuel Leaks (Inside of Engine) and Fuel Leaks (Outside of Engine) Diagnostics

SMU - Fuel Leaks (Inside of Engine) and Fuel Leaks (Outside of Engine) Diagnostics

Subject:Fuel Leaks (Inside of Engine) and Fuel Leaks (Outside of Engine) Diagnostics

Models:2001 Chevrolet and GMC C/K Pickup Models (Silverado, Sierra)
with 6.6L Engine (VIN 1 -- RPO LB7)


This bulletin is being issued to add the Fuel Leaks (Inside of Engine) and Fuel Leaks (Outside of Engine) diagnostics in the Engine Controls-6.6L sub-section of the Service Manual.

The following information has been updated within SI. If you are using a paper version of this Service Manual, please make a reference to this bulletin on the affected page.

Fuel Leaks (Inside of Engine)

Important: If you were directed here from Fuel Return System Diagnosis, go to step 15. This will be performed with the same components disconnected as stated in that test.


    Object Number: 761597 Size: SH
  1. Disconnect the fuel return line (1) at the engine. Refer to Quick Connect Fittings Service (Metal Collar).
  2. Remove the air duct from the air cleaner assembly to the turbo inlet.
  3. Remove the air intake pipe. Refer to Air Intake Pipe Replacement.

    4. Object Number: 744233 Size: SH
  4. Remove the fuel return rubber hose of the fuel injection pump from the junction block (2). Cap the fitting on the block with a 9.53 mm (3/8 in) rubber cap (1) to prevent fuel leakage.
  5. Install the J 23738-A Vacuum Pump at the fuel return pipe.
  6. Apply 50.8 kPa (15 inches Hg) of vacuum to the pipe.
    7. • If the vacuum holds, go to step 23.
    • If the vacuum does not hold, go to step 7.
  7. Remove the generator. Refer to Generator Replacement in Engine Electrical.

    8. Object Number: 761695 Size: SH
  8. Disconnect the fuel return line (1) from the right front cylinder head and left rear cylinder heads.

    9. Object Number: 844173 Size: SH
  9. Install the black hose (1) from the J 45873 on to each cylinder head return port and install the J 23738-A onto the black hose on the right cylinder head.
  10. Apply 50.8 kPa (15 inches Hg) of vacuum to the port.
  11. Install the J 23738-A to the black hose on the left cylinder head return port and apply 50.8 kPa (15 inches Hg) of vacuum.
    12. • If the vacuum holds on both sides, replace the fuel return line between the cylinder head return ports.
    •  If the vacuum does not hold on one or both sides, go to step 12.
  12. Perform the lower valve cover removal procedure for the bank(s) that did not hold vacuum. Refer to Valve Rocker Arm Cover Replacement-Lower Right and Valve Rocker Arm Cover Replacement-Lower Left in Engine Mechanical. Then go to step 13.
  13. Connect the fuel return line to both cylinder heads.

    14. Tighten
    Tighten the bolts to 15 N·m(11 lb.ft).


    Object Number: 820461 Size: SH
  14. Install the J 42964-1 9.53 mm (3/8 in) Fuel Pipe Shutoff Valve (2) to the fuel return line (1).
  15. Install the J 35800-A Fuel Injector Cleaner on the J 42964-1 3/8 Fuel Pipe Shutoff Valve port closest to the fuel return line.
  16. Ensure that the shutoff valve is closed.
  17. Add 0.296L (10 ounces) of diesel fuel and 0.118L (4 ounces) of oil dye to the J 35800-A Fuel Injector Cleaner.
  18. Connect the shop air supply to the J 35800-A.
  19. Adjust the pressure regulator on the J 35800-A to 103 kPa (15 psi).
  20. Clean the fuel injectors and fuel return lines with brake cleaning solvent and let dry.
  21. Open the valve on the bottom of the J-35800-A fuel injector cleaner canister.
  22. Inspect for leaks around the fuel injectors and the spill lines with a J 28428-E High Intensity Black Light Kit. Then go to step 29.
  23. Remove both upper valve covers. Refer to Valve Rocker Arm Cover Replacement-Upper Left and Valve Rocker Arm Cover Replacement-Upper Right in Engine Mechanical.
  24. Install the fuel injector feed pipes.

    25. Tighten
    Tighten the fuel feed pipes to 44 N·m (32 lb.ft.).

  25. Add 0.237L (8 ounces) of oil dye to the fuel tank. On dual tank systems, add the dye to the front, or primary, tank. Refer to Fuel System Description.
  26. Start the engine.
  27. Increase the fuel pressure to 160 MPa with a scan tool.
  28. Inspect for leaks around the fuel injectors with a J 28428-E High Intensity Black Light Kit. Then go to step 29.
  29. Tighten or replace any leaking components or gaskets.
  30. Perform the lower valve cover installation procedures as necessary. Refer to Valve Rocker Arm Cover Replacement-Lower Left and Valve Rocker Arm Cover Replacement-Lower Right in Engine Mechanical .

Fuel Leaks (Outside of Engine)

    Object Number: 658266 Size: SH
  1. Remove the upper intake manifold sight shield using the following procedure:
    2. 1.1. Remove the retaining bolt in the front of the shield.
    1.2. Lift up on the front of the shield.
    1.3. Lift the shield off the rear bracket.
  2. Clean all of the fuel lines between the fuel injection pump and the fuel injectors using brake cleaning solvent, and let dry.
  3. Add 0.237L (8 ounces) of oil dye to the fuel tank. On dual tanks, add the dye to the front, or primary, tank. Refer to Fuel System Description.
  4. Connect a scan tool to the DLC.
  5. Start and idle the engine for 3-5 minutes.
  6. Command the fuel pressure control to 160 MPa (23,206 psi) with a scan tool.
  7. Inspect for fuel leaks around the fuel injection pump, junction block, fuel rails, and fuel injector supply lines with a J 28428-E High Intensity Black Light Kit.

    8. Tighten or replace any leaking lines or components. Refer to the following:

    • Fuel Injection Line Routing Diagram
    • Fastener Tightening Specifications
    • Fuel Rail Assembly Replacement-Bank 1
    • Fuel Rail Assembly Replacement-Bank 2
    • Fuel Junction Block Replacement
    • Fuel Injection Pump Replacement