Fuel Line - High Pressure

This procedure covers replacement of the high-pressure fuel line running from the fuel injection pump to the fuel rail on the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• High pressure fuel line assembly × 1 — Use OEM Mopar specification for 5.9L Cummins
• Fuel line sealing washers/crush washers × 4 — Use OEM specification - typically included with line

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 (minimum 2 hours)
4. Place fire extinguisher within immediate reach of work area
5. Prepare clean workspace and lay out clean shop towels
6. Position drain pan and fuel catch container under fuel injection pump area
7. Photograph or diagram all fuel line routing and connections before disassembly

Procedure

1. 1

   Relieve fuel system pressure
   Although no specific pressure relief procedure exists for this system, allow vehicle to sit with batteries disconnected for at least 30 minutes. This allows some pressure dissipation. Be aware that significant pressure will still be present when lines are opened.
2. 2

   Access high-pressure fuel line
   Open hood and secure with prop rod. Locate the high-pressure fuel line running from the injection pump (driver side of engine) to the fuel rail on top of the engine. Remove any engine covers or air intake components that obstruct access. On some configurations, you may need to remove or loosen the intercooler tube for better access.
3. 3

   Clean connection areas
   Use wire brush to thoroughly clean all fittings at both ends of the high-pressure line. Remove all dirt, corrosion, and debris around the fittings to prevent contamination from entering the fuel system. Spray fittings with penetrating oil if corrosion is present and allow to soak for 10-15 minutes.
4. 4

   Position fuel containment
   Wrap multiple shop towels around the injection pump end connection. Position drain pan directly below. Ensure adequate fuel containment as diesel will spray and drain when connection is loosened. Have additional clean towels ready.
5. 5

   Disconnect line at injection pump
   Using proper size flare nut wrench, carefully loosen the high-pressure line fitting at the injection pump outlet. Turn slowly and expect fuel to spray initially. Once loose, allow fuel to drain completely into towels and pan. Remove fitting completely and immediately cap or plug the injection pump outlet with a clean plug to prevent contamination. Cap the end of the disconnected line as well.
6. 6

   Disconnect line at fuel rail
   Reposition towels and drain pan under the fuel rail connection. Using flare nut wrench, loosen the high-pressure line fitting at the fuel rail inlet. Again, expect fuel discharge. Once loose, allow complete drainage. Remove the line completely from vehicle. Immediately cap or plug the fuel rail inlet to prevent any debris from entering the system.
7. 7

   Inspect and clean connection points
   With line removed, inspect both the injection pump outlet and fuel rail inlet for any debris, metal particles, or damage. Wipe both connection points clean with lint-free shop towels. Inspect mating surfaces for scratches, corrosion, or damage that could prevent proper sealing.
8. 8

   Prepare new fuel line
   Remove new high-pressure fuel line from packaging. Verify it matches the old line in length, fitting sizes, and routing configuration. Verify the sealing method for this line — Cummins high-pressure common rail lines typically use metal-to-metal conical flare seats rather than crush washers. Confirm against the service manual whether any sealing washers are required. Keep all protective caps on line ends until immediately before installation. Do not remove caps until ready to connect to prevent any contamination.
9. 9

   Install new line at injection pump
   Remove cap from injection pump outlet and from pump end of new line. Install new sealing washer onto fitting. Carefully thread the new line onto the injection pump outlet by hand, ensuring threads engage properly without cross-threading. Hand tighten until fitting seats, then use flare nut wrench to tighten firmly. Torque the fitting to the factory specification (verify in the Mopar service manual for this engine — typically approximately 28-33 ft-lbs / 38-45 Nm for the high-pressure line nuts). Do not guess; under- or over-torquing a common rail fitting can cause dangerous high-pressure leaks or crack the line.
10. 10

    Route and secure new line
    Route the new fuel line following the same path as the original, ensuring it does not contact hot exhaust components, sharp edges, or moving parts. Verify adequate clearance from alternator, belts, and other accessories. The line should have gentle bends without kinks or tight radius curves.
11. 11

    Connect line at fuel rail
    Remove cap from fuel rail inlet and from rail end of new line. Install new sealing washer onto fitting. Thread fitting onto fuel rail inlet by hand to ensure proper engagement. Hand tighten until seated, then torque to the factory specification (verify in the Mopar service manual — typically approximately 28-33 ft-lbs / 38-45 Nm). Do not overtighten and do not under-torque a high-pressure common rail fitting.
12. 12

    Verify installation and clearances
    Double-check that both fittings are properly tightened and that new sealing washers were installed at each connection. Verify the line routing has proper clearance from all moving parts, hot surfaces, and sharp edges. Ensure no stress or pulling exists on the line at either connection point.
13. 13

    Reconnect batteries and prime system
    Reconnect positive battery cable first, then negative cable. The CP3 injection pump is not self-priming for large air volumes. Cycle the ignition key to RUN to activate the in-tank lift pump (it runs briefly at key-on), then OFF, repeating several times to help fill the low-pressure side. Consult the service manual for the correct air-bleed/priming procedure for this system.
14. 14

    Initial leak check preparation
    Place clean cardboard or white paper under both fuel line connections. Ensure drain pan is still positioned below work area. Have fire extinguisher immediately accessible. Clear all tools and flammable materials away from engine bay.
15. 15

    Start engine and check for leaks
    Start the engine. It may take extended cranking (up to 15-20 seconds) for the system to purge air and start. Once running, immediately inspect both connections using cardboard (never hands) to check for fuel spray. Look for any wetness or drips on the cardboard under connections. If any leak is detected, immediately shut off engine, relieve pressure, and re-tighten or inspect connection. If no leaks are visible after 30 seconds of running, proceed to verification steps.

Reassembly

1. Reinstall any air intake components, intercooler tubes, or engine covers that were removed for access
2. Clean up any spilled diesel fuel from engine bay and surrounding areas using appropriate absorbent materials
3. Dispose of fuel-soaked towels and materials properly according to local regulations

Verification

• With engine at operating temperature, inspect both fuel line connections again for any signs of seepage or leaks using the cardboard method
• Check for any fuel odor around the engine bay that would indicate a small leak
• Verify engine runs smoothly with no misfires, excessive smoke, or performance issues that could indicate air in the system
• Test drive vehicle and verify normal power delivery and no fuel system warning lights
• After test drive, perform final visual inspection of both connections with engine off but still warm - look for any fuel residue or wetness
• Re-inspect connections after 24 hours of normal driving to ensure no delayed leaks develop

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