Front Pipe

Replacement of the front exhaust pipes on the M275 6.0L V12 BiTurbo engine, connecting the turbocharger outlets to the catalytic converters.

Warnings

Tools required

Parts

• Front pipe assembly (left bank) × 1 — A2754901820 or equivalent
• Front pipe assembly (right bank) × 1 — A2754901920 or equivalent
• Turbocharger to front pipe gaskets × 2 — Use OEM specification
• Front pipe to catalytic converter gaskets × 2 — Use OEM specification
• Exhaust flange nuts/bolts (if corroded) × 8 — M10x1.5 exhaust hardware
• Anti-seize compound × 1 — Copper or nickel-based

Preparation

1. Ensure engine and exhaust system are completely cold to the touch
2. Raise vehicle on lift or secure on jack stands at all four corners, ensuring adequate clearance for underside access
3. Spray all exhaust flange bolts, O2 sensor threads, and heat shield fasteners with penetrating oil
4. Remove engine undertrays and heat shields as necessary for access to front pipes
5. Disconnect negative battery terminal to prevent O2 sensor fault codes during removal

Procedure

1. 1

   Remove heat shields
   Remove the heat shields covering the front pipes and turbocharger outlet areas. These are typically secured with multiple bolts along the underside. Keep track of all fasteners and brackets for reinstallation.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
2. 2

   Disconnect oxygen sensors
   Locate the oxygen sensors in the front pipes (one per bank, typically positioned downstream of turbochargers). Disconnect the electrical connectors by releasing the locking tabs. Using an oxygen sensor socket, carefully unthread the sensors from the front pipes. Turn counterclockwise and apply steady pressure - avoid shocking or impacting the sensors.
   ⚠Do not allow O2 sensors to hang by their wiring. Support them or set aside carefully to avoid internal damage.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
3. 3

   Disconnect exhaust hangers
   Locate the rubber exhaust hangers supporting the front pipes and catalytic converter assembly. Use a pry bar or lever to release the hangers from their mounting points. This will provide movement flexibility in the exhaust system.
   Torque spec

   Hanger Bolts27 Nm (20 lb-ft)
4. 4

   Remove downstream flange connection
   Locate the flange connection between the front pipes and the catalytic converters. Remove the flange bolts (typically 3-4 bolts per side) connecting the front pipes to the downstream catalytic converter assembly. Support the exhaust system to prevent it from dropping.
   ⚠Have an assistant support the exhaust or use a transmission jack to prevent the catalytic converter section from dropping when the connection is separated.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
5. 5

   Remove left bank (passenger side) turbocharger flange
   Access the flange connection between the left turbocharger outlet and the front pipe. Remove the exhaust flange bolts connecting the turbocharger to the front pipe. There are typically 3 bolts in a triangular pattern. Work may require universal joint adapters or extension bars due to limited access around the V12 engine bay.
   ℹ️Access is extremely tight on both banks of the V12. Take your time and use appropriate extensions and universal joints to avoid rounding fasteners.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
6. 6

   Remove left front pipe assembly
   With all connections disconnected, carefully maneuver the left bank front pipe assembly out from underneath the vehicle. It may need to be rotated or angled to clear surrounding components. Inspect the old gaskets and remove any residual gasket material from the turbocharger flange and catalytic converter flange.
7. 7

   Remove right bank (driver side) turbocharger flange
   Access the flange connection between the right turbocharger outlet and the front pipe. Remove the exhaust flange bolts connecting the turbocharger to the front pipe. Use the same techniques as the left side, working carefully in the confined space.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
8. 8

   Remove right front pipe assembly
   Carefully maneuver the right bank front pipe assembly out from underneath the vehicle. Clean all mating surfaces on both turbocharger outlets and catalytic converter inlets using a wire brush. Ensure surfaces are flat and free of carbon buildup, old gasket material, or corrosion.
9. 9

   Prepare new front pipes
   Unpack new front pipe assemblies and verify correct fitment for left and right banks (they are not interchangeable). Install new turbocharger outlet gaskets and catalytic converter inlet gaskets on the new pipes. Apply a thin coat of anti-seize compound to all exhaust flange bolt threads.
   ℹ️Do not reuse old exhaust gaskets. Always install new gaskets to ensure proper seal and prevent exhaust leaks.
10. 10

    Install right bank front pipe
    Position the new right bank front pipe assembly into place, aligning the turbocharger outlet flange and catalytic converter inlet flange. Start all bolts by hand before tightening any. Once all bolts are hand-started at both flanges, torque the turbocharger flange bolts first in a star pattern, then torque the catalytic converter flange bolts in a star pattern.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
11. 11

    Install left bank front pipe
    Position the new left bank front pipe assembly into place, aligning the turbocharger outlet flange and catalytic converter inlet flange. Start all bolts by hand before tightening any. Once all bolts are hand-started at both flanges, torque the turbocharger flange bolts first in a star pattern, then torque the catalytic converter flange bolts in a star pattern.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
12. 12

    Reinstall exhaust hangers
    Reconnect all rubber exhaust hangers to their mounting points. This will properly support the exhaust system and reduce vibration transfer to the chassis. Ensure the exhaust system hangs naturally without binding or stress points.
    Torque spec

    Hanger Bolts27 Nm (20 lb-ft)
13. 13

    Reinstall oxygen sensors
    Apply a small amount of anti-seize compound to the oxygen sensor threads only (do not contaminate the sensor tip). Thread each oxygen sensor into the new front pipes by hand, then torque to specification using the oxygen sensor socket. Reconnect the electrical connectors and ensure they click securely into place.
    ⚠Apply anti-seize only to threads. Keep anti-seize away from the sensor tip as contamination will cause sensor failure.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
14. 14

    Reinstall heat shields
    Reinstall all heat shields removed during disassembly. Ensure shields are properly positioned and not in contact with moving components. Torque all heat shield bolts to specification.
    Torque spec

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

    Final inspection and reconnection
    Reinstall any engine undertrays removed during preparation. Reconnect the negative battery terminal. Perform a final visual inspection of all connections, ensuring no tools or parts have been left in the engine bay or exhaust system.

Reassembly

1. Verify all exhaust flange connections are tight and properly torqued in a star pattern to ensure even gasket compression
2. Confirm all oxygen sensor electrical connectors are fully seated and locked
3. Ensure heat shields are properly installed and not rattling or in contact with exhaust components
4. Check that exhaust hangers are properly supporting the system with no excessive stress or binding

Verification

• Start the engine and allow it to idle. Listen carefully for any exhaust leaks at the turbocharger flanges and catalytic converter flanges
• Check for unusual vibrations or rattling noises that could indicate loose heat shields or improper hanger installation
• Verify no check engine light or oxygen sensor fault codes are present using a diagnostic scanner
• Perform a test drive and monitor for proper turbocharger boost pressure and smooth power delivery through the RPM range
• After the first heat cycle, re-inspect all flange connections from underneath for signs of exhaust leaks (soot staining)
• Consider re-torquing exhaust flange bolts after 50-100 miles of driving as they may settle slightly with heat cycling

More procedures for this vehicle