Downpipe

This procedure covers removal and replacement of the downpipe (exhaust pipe between turbocharger and catalytic converter/mid-pipe) on the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• Downpipe assembly (turbo to mid-pipe) × 1 — Aftermarket or OEM replacement
• Exhaust gasket (turbo to downpipe) × 1 — Use OEM specification
• Exhaust gasket (downpipe to mid-pipe) × 1 — Use OEM specification
• Oxygen sensor (if reusing, inspect condition) × 1 — Downstream O2 sensor
• Anti-seize compound (nickel-based) × 1 — High-temperature rated

Preparation

1. Park vehicle on level surface and allow exhaust system to cool completely (minimum 2 hours)
2. Apply wheel chocks to rear wheels
3. Raise front of vehicle with floor jack and support on jack stands at frame rails
4. Spray all exhaust flange bolts, hanger bolts, and O2 sensor with penetrating oil and allow to soak for 15-30 minutes
5. Disconnect negative battery cable if replacing O2 sensor to prevent fault codes

Procedure

1. 1

   Disconnect oxygen sensor
   This diesel application does not use an oxygen sensor on the downpipe. Skip this step. Note: pre-2007 5.9L Cummins engines have no exhaust O2 sensor; if any exhaust temperature (EGT) probe or sensor is present in the pipe, disconnect its connector and carefully remove it before proceeding.
2. 2

   Remove heat shield (if equipped)
   Some models have a heat shield covering portions of the downpipe. Remove heat shield mounting bolts using appropriate socket. Set heat shield aside for reinstallation.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
3. 3

   Disconnect downpipe from turbocharger outlet
   Locate the exhaust flange connection between turbocharger outlet and downpipe inlet. On most factory HX35/HY35 applications this is a 4-bolt flange at the turbo outlet; some aftermarket or later HE351 turbos use a V-band clamp. Verify your specific turbo outlet configuration before removal. Remove the fasteners securing the connection. You may need to support the downpipe weight with a jack or helper. Separate the joint carefully, working the downpipe free from the turbo outlet. Remove and discard the old gasket.
   ⚠Turbo outlet flange studs are prone to breaking. Apply penetrating oil and use gradual turning force.
   Torque spec

   Exhaust Flange Bolt45 Nm (33 lb-ft)
4. 4

   Support downpipe weight
   Position a floor jack with a block of wood under the downpipe to support its weight while you disconnect the remaining connections. This prevents stress on the remaining mounting points.
5. 5

   Disconnect exhaust hangers
   Locate rubber exhaust hangers supporting the downpipe. Remove hanger bolts or unhook rubber isolators from their mounting brackets as applicable. Most 2nd generation Rams use bolt-on hangers at the transmission crossmember area.
   Torque spec

   Hanger Bolts20 Nm (15 lb-ft)
6. 6

   Disconnect downpipe from mid-pipe/catalytic converter
   Locate the flange connection at the rear of the downpipe where it connects to the exhaust pipe. Note: these pre-emissions 5.9L Cummins trucks do not have a catalytic converter. Remove the flange bolts securing this connection. Separate the joint and remove the old gasket. The downpipe should now be free to remove.
7. 7

   Remove downpipe from vehicle
   With all connections disconnected, carefully maneuver the downpipe out from under the vehicle. It may need to be rotated or angled to clear the transmission crossmember, driveshaft, and other components. Lower the jack supporting the downpipe as you remove it.
8. 8

   Clean mating surfaces
   Use a wire brush and scraper to thoroughly clean all exhaust flange mating surfaces on the turbocharger outlet, mid-pipe inlet, and any other connection points. Remove all old gasket material, carbon deposits, and rust. Clean surfaces ensure proper sealing and prevent exhaust leaks.
9. 9

   Prepare new downpipe and install oxygen sensor
   This diesel application has no oxygen sensor to install. If your downpipe has an EGT probe bung, apply high-temp anti-seize to the probe threads, thread it in by hand, and tighten to the probe manufacturer's specification.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
10. 10

    Position new downpipe
    Position the new downpipe under the vehicle, using a floor jack to support its weight. Align the downpipe so all connection points are accessible. Install new gaskets at both the turbo outlet connection and the mid-pipe connection (do not reuse old gaskets).
11. 11

    Connect downpipe to mid-pipe
    Align the downpipe rear flange with the mid-pipe or catalytic converter inlet flange. Install new gasket between flanges. Apply anti-seize compound to flange bolt threads. Start all flange bolts by hand, then tighten in a cross-pattern to ensure even gasket compression. Torque to specification.
12. 12

    Connect downpipe to turbocharger
    Align the downpipe front flange with the turbocharger outlet. Install new gasket between flanges. Apply anti-seize compound to exhaust flange bolt threads. Start all fasteners by hand to ensure proper alignment, then tighten evenly in a cross-pattern. Torque to specification.
    Torque spec

    Exhaust Flange Bolt45 Nm (33 lb-ft)
13. 13

    Install exhaust hangers
    Reconnect all exhaust hangers and rubber isolators. Ensure the downpipe hangs properly without binding or stress. Install hanger bolts and torque to specification. The exhaust system should have slight flexibility but not be loose or sagging.
    Torque spec

    Hanger Bolts20 Nm (15 lb-ft)
14. 14

    Reinstall heat shield and connect oxygen sensor
    If equipped with a heat shield, reinstall it and torque mounting bolts to specification. If an EGT probe was removed, reconnect its harness and route the wire away from hot exhaust components, securing with any factory clips.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)
15. 15

    Final inspection
    Visually inspect all connections to ensure fasteners are tight and gaskets are properly seated. Check for adequate clearance between the downpipe and driveshaft, frame rails, crossmembers, and brake lines. Reconnect negative battery cable if disconnected.

Reassembly

1. Ensure all exhaust connections are tight and gaskets are properly installed
2. Verify oxygen sensor connector is fully seated and wire is routed safely
3. Confirm downpipe has adequate clearance from all surrounding components
4. Lower vehicle from jack stands carefully

Verification

• Start engine and allow to idle, listening for exhaust leaks at all connection points
• Check for visible exhaust smoke escaping from flanges or connections
• Rev engine slightly and verify no rattles or contact between downpipe and chassis components
• Test drive vehicle and monitor for unusual exhaust noise or check engine light
• After test drive, re-inspect all connections while exhaust is warm to ensure no leaks developed

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