Complete replacement of all six fuel injectors on the 6.7L Cummins diesel engine, including fuel rail removal and high-pressure fuel system disassembly.

Warnings

Tools required

Parts

• Fuel injector × 6 — Use OEM Cummins specification
• Fuel rail O-ring kit × 1 — Use OEM specification
• High-pressure fuel line O-rings × 6 — Use OEM specification
• Fuel return line O-rings × 6 — Use OEM specification
• Valve cover gasket (if damaged) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect both negative battery cables to prevent accidental starting
3. Allow engine to cool completely if recently operated
4. Remove engine cover by loosening cover screws
5. Clean the valve cover and surrounding area thoroughly to prevent debris entry
6. Have adequate lighting and workspace access to the top of the engine
7. Place drain pan under work area to catch fuel spillage

Procedure

1. 1

   Depressurize fuel system
   Turn ignition key to ON position without starting engine, then back to OFF. Repeat this cycle three times to allow fuel system to pressurize and depressurize through the pressure relief valve. This reduces residual pressure in the high-pressure fuel rails. Wait 10 minutes before proceeding.
2. 2

   Disconnect fuel supply and return lines
   Locate the fuel supply and return lines at the rear of the fuel rail assembly. Use fuel line disconnect tools to release the quick-connect fittings. Cap or plug all open fuel lines immediately to prevent contamination. Have shop towels ready as residual fuel will drain from lines.
3. 3

   Remove valve cover
   Remove valve cover mounting bolts in a crisscross pattern starting from the outside working inward. Carefully lift valve cover away from cylinder head. Inspect gasket condition and replace if damaged. Cover the open valve train area with clean shop towels to prevent debris entry.
   ⚠Keep all debris and tools away from the open valve train area. Foreign objects can cause catastrophic engine damage.
   Torque spec

   Mounting Bolts37 Nm (27 lb-ft)
4. 4

   Disconnect injector electrical connectors
   Disconnect the electrical connector from each of the six fuel injectors. Press the release tab and pull straight up to avoid damaging the connector pins. Move wiring harness aside and secure it away from the work area.
5. 5

   Remove high-pressure fuel lines
   Starting from cylinder 1, use high-pressure fuel line wrenches to loosen and remove the fuel line fittings at both the injector and fuel rail ends. Lines must be removed as complete assemblies. Work carefully to avoid bending or damaging the hardlines. Place removed lines on clean shop towels.
   ⚠High-pressure fuel lines are precision-machined components. Do not reuse lines that are bent, damaged, or have damaged fittings.
   Torque spec

   Fuel Line Fittings25 Nm (18 lb-ft)
6. 6

   Remove fuel return lines
   Loosen hose clamps on the fuel return lines connecting each injector. Carefully disconnect the return lines from each injector and move them aside. Note the routing for reinstallation.
   Torque spec

   Hose Clamps3 Nm (2 lb-ft)
7. 7

   Remove fuel rail assembly
   Remove the fuel rail mounting bolts securing the rail to the cylinder head. There are typically three bolts along the rail. Carefully lift the fuel rail assembly straight up and away from the cylinder head. Set aside on clean workspace.
   Torque spec

   Fuel Rail Bolts12 Nm (9 lb-ft)
8. 8

   Extract fuel injectors
   Each injector is held in the cylinder head by a clamp. Remove the clamp bolt for each injector. Use a pry bar or injector removal tool to carefully work each injector out of its bore. Injectors may be tight due to O-ring compression and carbon buildup. Work slowly and evenly to avoid damaging the injector bore.
   ⚠Do not scratch or gouge the injector bore in the cylinder head. Damage to this sealing surface will cause combustion gas leaks and poor injector performance.
9. 9

   Clean injector bores
   Use a wire brush and compressed air to thoroughly clean each injector bore in the cylinder head. Remove all carbon deposits, old O-ring material, and debris. The bore must be completely clean for proper seating of new injectors. Wipe bores with clean, lint-free shop towels.
10. 10

    Prepare new injectors
    Remove new injectors from packaging only when ready to install. Inspect each injector for shipping damage. Install new O-rings on each injector, lubricating lightly with clean diesel fuel. Do not use petroleum-based lubricants. Verify each injector has the correct part number for this engine.
11. 11

    Install new fuel injectors
    Install each new injector into its corresponding bore in the cylinder head, ensuring proper orientation. Press injector down firmly until it seats completely. Install the injector clamp and bolt, tightening to specification. Apply light anti-seize to clamp bolt threads if desired. Install all six injectors before proceeding.
12. 12

    Reinstall fuel rail assembly
    Install new O-rings on fuel rail connections. Position fuel rail assembly over the installed injectors, ensuring proper alignment with each injector connection point. Install fuel rail mounting bolts and tighten in a crisscross pattern to specification.
    Torque spec

    Fuel Rail Bolts12 Nm (9 lb-ft)
13. 13

    Reconnect high-pressure fuel lines
    Install new O-rings on all fuel line fittings. Install high-pressure fuel lines to each injector and to the fuel rail, hand-tightening fittings first. Use high-pressure fuel line wrenches to tighten line fittings to specification. Tighten in two stages: first to 50% torque, then to final torque specification.
    Torque spec

    Fuel Line Fittings25 Nm (18 lb-ft)
14. 14

    Reconnect fuel return lines and electrical connectors
    Reconnect fuel return lines to each injector, following original routing. Install hose clamps and tighten to specification. Reconnect electrical connectors to each injector, ensuring positive engagement with an audible click.
    Torque spec

    Hose Clamps3 Nm (2 lb-ft)
15. 15

    Reinstall valve cover and fuel supply lines
    Remove protective coverings from valve train area. Install valve cover with gasket, tightening mounting bolts in a crisscross pattern from center outward to specification. Reconnect fuel supply and return lines at the rear of the fuel rail, using new O-rings. Tighten fuel line fittings to specification. Reinstall engine cover.
    Torque spec

    Mounting Bolts37 Nm (27 lb-ft)

    Fuel Line Fittings25 Nm (18 lb-ft)

    Cover Screws15 Nm (11 lb-ft)

Reassembly

1. Ensure all electrical connectors are fully seated and locked
2. Verify all fuel line connections are tight and properly torqued
3. Confirm no tools or shop towels were left in engine compartment
4. Reconnect both negative battery cables

Verification

• Turn ignition to ON position (do not start) and listen for fuel pump priming. Repeat 3-4 times to build fuel pressure
• Inspect all fuel connections for leaks before starting engine
• Start engine and allow to idle. Monitor for smooth operation and absence of fuel leaks
• Check for diagnostic trouble codes using scan tool. Clear any codes related to injector replacement procedure
• Perform a test drive to verify proper engine performance under load
• Re-inspect all connections after test drive for any signs of fuel seepage
• Monitor engine operation over the next several days for any irregularities

More procedures for this vehicle