Exhaust Gasket - Rear

Replace the rear exhaust gasket between the catalytic converters and rear exhaust pipe on a 2011-2014 Ford F-150 3.5L EcoBoost 4WD.

Warnings

Tools required

Parts

• Exhaust flange gasket (rear converter to muffler) × 1 — Use OEM specification
• Exhaust flange bolts/nuts × 4 — Replace if corroded

Preparation

1. Park vehicle on level surface and apply parking brake
2. Allow exhaust system to cool completely for at least 2 hours
3. Raise vehicle using floor jack and support on jack stands at frame rails behind front wheels
4. Spray all exhaust flange bolts and oxygen sensor with penetrating oil and let soak for 15-30 minutes
5. Remove any heat shields that obstruct access to the rear exhaust flange connection

Procedure

1. 1

   Remove heat shields if necessary
   If present, remove the heat shield bolts securing any shields that block access to the rear exhaust flange. The flange is located approximately 18 inches behind the catalytic converters, near the transmission crossmember. Keep hardware organized for reinstallation.
   Torque spec

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

   Support the rear exhaust section
   Place a jack stand or transmission jack under the rear muffler section to support its weight once the flange is disconnected. This prevents stress on the exhaust hangers and makes alignment easier during reassembly.
   ⚠Do not allow the exhaust to hang unsupported by rubber hangers only, as this can damage the hangers or misalign the system.
3. 3

   Remove oxygen sensor if obstructing access
   If the downstream oxygen sensor interferes with access to the rear flange bolts, disconnect the electrical connector and remove the sensor using an oxygen sensor socket or 22mm wrench. Turn counterclockwise to remove. Inspect sensor threads and clean if reusing.
   ℹ️Mark the sensor orientation before removal to ensure proper reinstallation angle.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
4. 4

   Remove rear exhaust flange bolts
   Using a 15mm socket with extensions, remove the 4 bolts connecting the catalytic converter outlet flange to the rear exhaust pipe flange. Work in a cross pattern (top-left, bottom-right, top-right, bottom-left) to prevent binding. If bolts are seized, apply heat carefully or use a breaker bar.
   ⚠Bolts may be severely corroded. If bolt heads round off or studs break, extraction may be required.
5. 5

   Separate exhaust flanges
   Once all bolts are removed, carefully separate the two exhaust flanges. You may need to tap gently with a rubber mallet or pry carefully with a flat bar. Lower the rear exhaust section slightly using the support jack to create clearance.
   ⚠Do not force the flanges apart excessively, as this can bend the pipes or damage threaded studs.
6. 6

   Remove old gasket and clean surfaces
   Remove the old gasket from both flange faces. Use a wire brush to thoroughly clean both mating surfaces, removing all carbon deposits, rust, and old gasket material. The surfaces must be flat and clean for proper sealing.
   ℹ️Inspect flange faces for warping or damage. Minor imperfections can be dressed with a file, but severely warped flanges require replacement.
7. 7

   Install new gasket
   Position the new exhaust gasket between the two flanges. Align the gasket bolt holes with the flange holes. Most gaskets have a reinforced metal ring and should be installed with any markings facing the rear of the vehicle.
   ℹ️Ensure the gasket is fully seated in the flange recess if applicable. Some gaskets are symmetrical, others have a specific orientation.
8. 8

   Reconnect exhaust flanges
   Raise the rear exhaust section using the support jack to align the flanges. Guide the gasket into position and align all bolt holes. Insert bolts finger-tight in a cross pattern to ensure even alignment before torquing.
   ⚠Do not force bolts through misaligned holes, as this can strip threads. Adjust exhaust position until all bolts thread easily.
9. 9

   Apply anti-seize and torque flange bolts
   Apply anti-seize compound to the threads of all exhaust flange bolts. Torque the bolts in a cross pattern (opposite corners) to 45 Nm (33 lb-ft). Make two passes: first to 20 Nm, then final torque to 45 Nm to ensure even gasket compression.
   ℹ️Even torque is critical to prevent gasket leaks. Always use a cross pattern when tightening.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
10. 10

    Reinstall oxygen sensor if removed
    If the oxygen sensor was removed, apply a thin coat of anti-seize to the sensor threads only (avoid the sensor tip). Thread the sensor in by hand, then torque to 45 Nm (33 lb-ft). Reconnect the electrical connector.
    ⚠Never apply anti-seize to the sensor tip, as this will contaminate it and cause false readings.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
11. 11

    Reinstall heat shields
    If heat shields were removed, reinstall them in their original positions and torque the bolts to 10 Nm (7 lb-ft).
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)
12. 12

    Remove support and lower vehicle
    Remove the jack or support from under the rear exhaust. Verify all exhaust hangers are properly seated. Lower the vehicle from jack stands and remove all tools from under the vehicle.

Reassembly

1. Double-check that all flange bolts are torqued to specification in a cross pattern
2. Ensure oxygen sensor electrical connector is fully seated and secured
3. Verify all heat shields are reinstalled and properly secured
4. Confirm exhaust system is not contacting the driveshaft, frame, or fuel tank

Verification

• Start the engine and listen for exhaust leaks at the rear flange connection. A leak will produce a ticking or hissing sound that increases with RPM
• With engine at operating temperature, visually inspect the flange joint for escaping exhaust gases (slight smoke or vapor)
• Rev the engine to 2500 RPM and verify no exhaust leak sounds are present
• Check that no exhaust odor is entering the cabin during test drive
• Verify no check engine light appears due to oxygen sensor issues

Related trouble codes on this vehicle

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