Replace the high-pressure fuel line connecting the CP3 injection pump to the fuel rail on the 6.7L Cummins diesel engine, requiring careful handling of high-pressure fuel system components.

Warnings

Tools required

Parts

• High-pressure fuel line assembly × 1 — Use OEM Mopar/Cummins specification
• Fuel line O-rings × 4 — Use OEM specification
• Banjo bolt sealing washers (if applicable) × 4 — Use OEM specification

Preparation

1. Park vehicle on level surface, engage parking brake, and allow engine to cool completely (minimum 2 hours)
2. Ensure adequate ventilation in work area
3. Place absorbent pads under fuel system components to catch spillage
4. Disconnect both negative and positive battery cables to prevent ignition sources
5. Remove engine cover by lifting from rear and pulling forward to release front clips
6. Clean all dirt and debris from around fuel line connections using compressed air and wire brush
7. Have replacement parts, O-rings, and tools organized and within reach before breaking any fuel connections

Procedure

1. 1

   Relieve fuel system pressure
   Allow engine to sit for minimum 1 hour after last operation to allow fuel pressure to bleed down naturally. The CP3 pump has an internal pressure relief that returns fuel to tank. Verify no fuel spray when loosening connections by placing shop towel over connection and slowly cracking fitting 1/8 turn. If pressure is present, wait longer.
   ⚠️Never attempt to relieve pressure by loosening injector lines or other connections while under pressure. Wait for natural pressure decay.
2. 2

   Identify and document fuel line routing
   Photograph or diagram the exact routing of the high-pressure fuel line from CP3 pump (driver side of engine) to the fuel rail (passenger side). Note any clips, brackets, or protective covers. The line runs across the front of the engine and includes mounting brackets that must be reinstalled in correct locations.
3. 3

   Disconnect fuel line at fuel rail
   Using appropriate flare nut wrench to prevent rounding, carefully loosen the fuel line fitting at the fuel rail connection (passenger side). Place shop towel around connection to catch residual fuel. Once loose, carefully unthread by hand. Remove and discard old O-rings from connection. Cap or plug the fuel rail port immediately with clean plastic plug to prevent contamination entry.
   ⚠Use only flare nut wrenches on these fittings. Standard open-end wrenches will round the soft brass/aluminum fittings.
4. 4

   Remove fuel line bracket fasteners
   Locate and remove all mounting brackets securing the high-pressure fuel line to the engine. Typically there are 2-3 bracket assemblies along the line route. Remove bracket bolts and retain for reinstallation. Keep track of bracket orientation and spacers if present.
   Torque spec

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

   Disconnect fuel line at CP3 pump
   At the driver side of engine, locate the high-pressure fuel line connection to the CP3 injection pump outlet. Using flare nut wrench, carefully loosen and remove the fitting. Place shop towel to catch residual fuel. Remove and discard old O-rings. Immediately cap or plug both the pump outlet and the fuel line end with clean plastic caps to prevent any contamination from entering the system.
   ⚠The CP3 pump outlet is particularly sensitive to contamination. Do not allow any dirt, debris, or foreign material near this connection.
6. 6

   Remove high-pressure fuel line
   Carefully maneuver the fuel line out of the engine bay, taking care not to drop it or allow the ends to contact any surfaces. Inspect the line routing path for any debris that may have accumulated and clean thoroughly. Inspect fuel rail and pump ports for damage, debris, or metal particles.
7. 7

   Inspect and clean connection points
   Thoroughly clean the fuel rail and CP3 pump connection threads and sealing surfaces using lint-free shop towels and approved parts cleaner. Inspect threads for damage or cross-threading. Inspect O-ring sealing surfaces for scoring, scratches, or damage. Any damage requires component replacement. Blow out ports with clean, dry compressed air if available.
   ⚠Never use shop air that may contain moisture or oil contamination. Use only filtered, dry compressed air or omit this step.
8. 8

   Prepare new fuel line
   Unpack new high-pressure fuel line carefully. Verify protective caps are in place on both ends until installation. Inspect line for any shipping damage, kinks, or deformation. Install new O-rings on both connection ends, lightly lubricating with clean diesel fuel. Do not use any petroleum-based lubricants or assembly lubes. Verify O-rings are seated properly in their grooves.
9. 9

   Install fuel line at CP3 pump
   Remove protective cap from pump end of new fuel line and from CP3 pump outlet immediately before connection. Carefully thread the fitting onto the CP3 pump outlet by hand, ensuring straight threading with no cross-threading. Hand-tighten until O-ring contact is felt, then use flare nut wrench and torque wrench to tighten to specification. Do not over-torque as this can damage sealing surfaces.
   ⚠If fitting does not thread smoothly by hand, do not force it. Remove and inspect for cross-threading or debris.
   Torque spec

   Fuel Line Fittings25 Nm (18 lb-ft)
10. 10

    Route and secure fuel line
    Route the new high-pressure fuel line along the same path as the original, ensuring no contact with sharp edges, hot exhaust components, or moving parts. Install all mounting brackets in their original positions, ensuring the line is properly seated in bracket clips. Verify adequate clearance from all surrounding components. Torque bracket bolts to specification.
    Torque spec

    Bracket Bolts27 Nm (20 lb-ft)
11. 11

    Connect fuel line at fuel rail
    Remove protective caps from fuel rail end of line and fuel rail port immediately before connection. Carefully thread the fitting onto the fuel rail port by hand, ensuring straight threading. Hand-tighten until O-ring contact is felt, then use flare nut wrench and torque wrench to tighten to specification. Verify line has no stress, twisting, or tension at either connection point.
    Torque spec

    Fuel Line Fittings25 Nm (18 lb-ft)
12. 12

    Inspect installation
    Perform final visual inspection of entire fuel line installation. Verify all brackets are secure, no part of the line contacts any moving or hot components, both connections are properly torqued, and there is no visible damage or stress on the line. Check that no tools or hardware have been left in engine bay.
13. 13

    Reconnect battery and prime system
    Reconnect positive battery cable first, then negative cable. Turn ignition key to ON position (do not crank) for 30 seconds to allow lift pump to prime the system. Turn key OFF, wait 10 seconds, then repeat ON cycle 3-4 times. This allows the low-pressure system to fill and purge air before starting.
14. 14

    Start engine and check for leaks
    With shop towels positioned around both high-pressure connections, start the engine. Immediately observe both connections for any sign of fuel seepage or spray. Let engine idle for 30 seconds during initial check. If any leak is detected, immediately shut down engine and investigate. If no leaks observed, allow engine to idle for 5 minutes while monitoring connections.
    ⚠️Stand clear of fuel line routing during initial start. High-pressure fuel spray is invisible and can penetrate skin. If leak is detected, do not attempt to tighten connections while engine is running.
15. 15

    Perform full pressure leak test
    After successful idle test, increase engine speed to approximately 1500 RPM for 2-3 minutes to bring system to full operating pressure. Carefully inspect all connections again with engine at elevated RPM. Shut down engine and perform final visual inspection of dry connections. Wipe all connections clean with white shop towel to verify no seepage. Reinstall engine cover.

Reassembly

1. Ensure engine cover clips are properly engaged at front mounting points before seating rear of cover
2. Verify no tools, rags, or parts remain in engine bay
3. Document repair date and mileage for maintenance records

Verification

• Start engine and verify smooth idle with no fuel smell or visible leaks at connections
• Check for diagnostic trouble codes using scan tool - there should be no fuel pressure or fuel system codes
• Test drive vehicle and verify normal power delivery and throttle response
• After test drive, perform final inspection of both fuel line connections for any seepage or wetness
• Monitor fuel system operation for next 100 miles and re-inspect connections if any fuel smell is detected

More procedures for this vehicle