Intake Manifold Gasket

This procedure replaces the intake manifold gasket on the 5.9L Cummins diesel engine, addressing air leaks that can cause rough idle, reduced power, and increased emissions.

Warnings

Tools required

Parts

• Intake manifold gasket × 1 — Use OEM specification
• Throttle body gasket (if equipped) × 1 — Inspect and replace if damaged

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery cable, then positive battery cable
3. Wait at least 2 minutes for electrical system discharge
4. Remove engine cover if equipped
5. Take photos of vacuum line routing, electrical connections, and fuel line positions for reference during reassembly

Procedure

1. 1

   Disconnect intake plumbing and air filter housing
   Loosen clamp at the turbocharger compressor inlet and disconnect the intake tube. Remove air filter housing assembly by disconnecting any mounting bolts and separating from turbocharger. Set aside in clean area.
2. 2

   Remove throttle body assembly
   This engine does not use a throttle body. Air intake on the 5.9L Cummins is unrestricted (no throttle plate); fueling is controlled electronically. Skip this step — there is no throttle body to remove.
   Torque spec

   Throttle Body Bolts10 Nm (7 lb-ft)
3. 3

   Disconnect fuel system components
   The 5.9L common-rail fuel system operates at extremely high pressure. Do NOT loosen the high-pressure fuel lines unless required — allow the system to depressurize per FSM procedure and observe all high-pressure fuel safety precautions. In most cases the fuel rail and high-pressure lines do not need to be disturbed to replace the intake manifold gasket; disconnect only what is necessary for manifold removal.
4. 4

   Remove fuel rail assembly
   On the 5.9L Cummins, the fuel rail mounts to the cylinder head and the injectors are retained in the head, connected via individual high-pressure lines. The fuel rail generally does not need removal to replace the intake manifold (grid heater) gasket. If access requires it, follow the FSM high-pressure fuel line and rail removal procedure.
   Torque spec

   Fuel Rail Bolts12 Nm (9 lb-ft)
5. 5

   Disconnect vacuum lines and electrical connections
   Disconnect any electrical connectors attached to intake manifold components (e.g., intake air temperature/manifold pressure sensor and the intake grid heater connections). Note that this diesel does not run vacuum lines off the intake manifold. Disconnect the EGR connection if equipped (2007 emissions configuration).
6. 6

   Remove intake manifold mounting bolts
   Remove all intake manifold mounting bolts in reverse order from center outward (opposite of tightening sequence). Refer to the FSM for the exact number of bolts securing the intake manifold/grid heater assembly on the 5.9L Cummins. Keep bolts organized and inspect for damage or thread wear.
   Torque spec

   Intake Manifold Bolts25 Nm (18 lb-ft)
7. 7

   Remove intake manifold
   Carefully lift intake manifold away from cylinder head. The manifold may be stuck to the gasket - gently work it loose with a plastic pry tool if needed, being careful not to damage sealing surfaces. Cover cylinder head ports immediately with clean rags or tape to prevent debris entry.
8. 8

   Clean gasket surfaces on cylinder head
   Use plastic gasket scraper to remove all old gasket material from cylinder head surface. Follow with nylon brush to remove residue. Clean surface thoroughly with brake cleaner and lint-free rags. Use shop vacuum to remove any debris. Inspect surface for damage, warping, or corrosion. Surface must be completely clean and dry.
9. 9

   Clean intake manifold mating surface
   Remove all old gasket material from intake manifold sealing surface using plastic scraper and nylon brush. Clean thoroughly with brake cleaner. Inspect manifold for cracks, especially around bolt holes and port openings. Ensure all passages are clear of debris.
10. 10

    Install new intake manifold gasket
    Remove protective covering from new gasket. Position gasket on cylinder head, ensuring proper orientation (check for UP markings or port alignment). Verify all bolt holes and ports align correctly. Gasket should lay flat without forcing - do not use gasket sealer unless specifically required by gasket manufacturer.
11. 11

    Install intake manifold
    Remove protective covering from cylinder head ports. Carefully lower intake manifold onto gasket, aligning all ports and bolt holes. Do not slide manifold once positioned as this can tear or displace gasket. Insert all mounting bolts finger-tight before proceeding to torque.
12. 12

    Torque intake manifold bolts
    Using a torque wrench, tighten the intake manifold/grid heater bolts to the Cummins FSM-specified torque and sequence for the 5.9L ISB (verify exact value against factory documentation before tightening). Tighten evenly in the specified pattern.
    Torque spec

    Intake Manifold Bolts25 Nm (18 lb-ft)
13. 13

    Reinstall fuel rail assembly
    If injectors were disturbed, follow the FSM injector installation procedure: seat injectors with new hold-down/seal components, install the injector hold-down clamps, and connect high-pressure lines torqued to Cummins specification (high-pressure lines are typically one-time-use and must be replaced). Do not press-fit injectors via the rail.
    Torque spec

    Fuel Rail Bolts12 Nm (9 lb-ft)
14. 14

    Reconnect fuel and electrical connections
    Reconnect fuel supply and return lines to fuel rail, ensuring connections are secure. Reconnect all fuel injector electrical connectors. Reconnect all vacuum lines to proper ports as documented in photos. Reconnect any intake manifold sensors or electrical connections.
15. 15

    Reinstall throttle body and intake system
    Reinstall the air filter housing and connect the intake tube to the turbocharger compressor inlet, tightening the clamp securely. (No throttle body, throttle position sensor, or throttle linkage is present on this diesel.)
    Torque spec

    Throttle Body Bolts10 Nm (7 lb-ft)

Reassembly

1. Reinstall engine cover if equipped
2. Reconnect positive battery cable, then negative battery cable
3. Double-check all electrical connections, vacuum lines, and fuel connections are secure
4. Verify no tools or rags were left in engine compartment

Verification

• Turn ignition to ON position without starting to pressurize fuel system. Check for fuel leaks at fuel rail connections
• Start engine and allow to idle. Listen for abnormal hissing sounds indicating intake air leaks
• Check for smooth idle quality - rough idle may indicate vacuum leak or improper gasket seating
• Rev engine gently and verify throttle response is normal with no hesitation
• Inspect all connections for leaks while engine is running
• Test drive vehicle to confirm normal power delivery and acceleration
• After test drive, recheck all bolts and connections for any signs of looseness or leakage

Related trouble codes on this vehicle

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