This procedure covers the removal and replacement of the high-pressure fuel rail assembly on the 6.7L Cummins diesel engine, including disconnection of fuel lines and injector connectors.

Warnings

Tools required

Parts

• Fuel rail assembly × 1 — Use OEM specification
• Fuel line O-rings × 4 — Use OEM specification
• Fuel rail mounting bolt seals (if equipped) × 6 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect both negative and positive battery cables to prevent accidental starter engagement
3. Allow engine to cool completely if recently operated
4. Remove engine cover by removing the cover screws
5. Place catch pans under work area to collect fuel spillage
6. Relieve fuel system pressure by loosening the fuel filter drain valve and allowing fuel to drain into a suitable container

Procedure

1. 1

   Remove engine cover
   Remove all cover screws securing the plastic engine cover. Lift the cover straight up to disengage any mounting grommets. Set aside in a clean area.
   Torque spec

   Cover Screws15 Nm (11 lb-ft)
2. 2

   Disconnect injector electrical connectors
   Locate all six fuel injector electrical connectors on top of the valve cover. Press the release tab on each connector and pull straight up to disconnect. Label or organize connectors to ensure correct reinstallation (cylinders 1-6 from front to rear).
3. 3

   Disconnect fuel supply and return lines
   Using the appropriate fuel line disconnect tool, disconnect the high-pressure fuel supply line from the inlet side of the fuel rail (driver side front). Also disconnect the fuel return line. Have shop towels ready as residual fuel will drain. Cap or plug open lines immediately to prevent contamination.
   ⚠Even with pressure relieved, fuel will spray initially. Wear safety glasses and gloves.
   Torque spec

   Fuel Line Fittings25 Nm (18 lb-ft)
4. 4

   Remove fuel rail bracket bolts
   Remove the bracket bolts securing the fuel rail support brackets. There are typically two brackets supporting the fuel rail assembly along its length. Remove bolts and set brackets aside.
   Torque spec

   Bracket Bolts27 Nm (20 lb-ft)
5. 5

   Remove fuel rail mounting bolts
   Locate and remove all six fuel rail mounting bolts that secure the fuel rail to the cylinder head. These bolts pass through the fuel rail and thread into the head between the injectors. Remove bolts in a gradual crisscross pattern to avoid binding.
   ℹ️Keep track of any sealing washers or seals on these bolts for reinstallation.
   Torque spec

   Fuel Rail Bolts12 Nm (9 lb-ft)
6. 6

   Remove fuel rail assembly
   Carefully lift the fuel rail assembly straight up and away from the cylinder head. The injectors may pull out with the rail or remain in the head depending on seal condition. Work the rail gently if resistance is felt. Once free, place the assembly on a clean workbench with injectors facing up to prevent contamination.
   ⚠Do not pry or twist the fuel rail excessively as this may damage injector seals or the rail itself.
7. 7

   Inspect injector bores and clean surfaces
   If injectors remained in the cylinder head, cover exposed injector bores with clean shop towels to prevent debris entry. Clean all sealing surfaces on the cylinder head where the fuel rail mounts. Use compressed air to blow away any debris from the area. Inspect O-ring grooves for damage.
8. 8

   Prepare new fuel rail assembly
   Install new O-rings on all fuel line connection points of the new fuel rail. Lubricate O-rings lightly with clean diesel fuel. Verify all mounting bolt holes are clear and threaded properly. If reusing injectors, transfer them to the new rail ensuring proper orientation and torque per injector installation specifications.
   ℹ️New O-rings are critical for proper sealing and must not be reused.
9. 9

   Install fuel rail assembly
   Carefully align the fuel rail assembly over the cylinder head, guiding injectors into their respective bores. Ensure the rail seats evenly and fully against the mounting surface. Do not force or cock the rail at an angle.
   ⚠Verify all injectors are properly aligned with their bores before applying downward pressure.
10. 10

    Install and torque fuel rail mounting bolts
    Install all six fuel rail mounting bolts with any required sealing washers. Thread bolts in by hand first to ensure proper engagement. Torque bolts to specification in a crisscross pattern starting from the center and working outward to ensure even seating.
    Torque spec

    Fuel Rail Bolts12 Nm (9 lb-ft)
11. 11

    Install fuel rail support brackets
    Reinstall the fuel rail support brackets in their original positions. Install bracket bolts and torque to specification.
    Torque spec

    Bracket Bolts27 Nm (20 lb-ft)
12. 12

    Reconnect fuel supply and return lines
    Remove caps or plugs from fuel lines. Connect the high-pressure fuel supply line and fuel return line to the fuel rail, ensuring connections are fully seated. Torque line fittings to specification using a flare nut wrench or line wrench to avoid rounding fittings.
    ⚠Ensure new O-rings are in place on all connections before tightening.
    Torque spec

    Fuel Line Fittings25 Nm (18 lb-ft)
13. 13

    Reconnect injector electrical connectors
    Reconnect all six injector electrical connectors in the correct order (cylinders 1-6 from front to rear). Ensure each connector clicks securely into place and locking tabs are fully engaged.
14. 14

    Prime fuel system and check for leaks
    Reconnect battery cables. Turn ignition key to the ON position (without starting) for 30 seconds to allow the lift pump to prime the fuel system. Repeat this cycle 3-4 times. Carefully inspect all fuel connections for leaks while the system is pressurized. Wipe up any spilled fuel.
    ⚠️Do not start engine if any fuel leaks are detected. Repair leaks immediately.

Reassembly

1. Reinstall engine cover with cover screws torqued to specification
2. Verify all tools and parts have been removed from engine bay
3. Dispose of old fuel-soaked rags and absorbent materials properly according to local regulations

Verification

• Start engine and allow to idle. Monitor for smooth operation with no misfires or rough running
• Check for fuel leaks at all connection points while engine is running at idle and at elevated RPM (1500-2000)
• Verify no diagnostic trouble codes (DTCs) are present using a scan tool
• Confirm proper fuel pressure readings if scan tool supports live data monitoring
• Test drive vehicle to verify normal operation under load and acceleration

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