This procedure covers removal and replacement of the exhaust flex pipe on a 2011-2014 Ford F-150 with 3.5L EcoBoost engine, including proper disconnection of oxygen sensors and exhaust component separation.

Warnings

Tools required

Parts

• Exhaust flex pipe assembly × 1 — Use OEM specification
• Exhaust flange gasket × 2 — Use OEM specification
• Flange bolts × 4 — Replace if damaged
• Exhaust clamps × 2 — Replace if damaged

Preparation

1. Park vehicle on level surface and apply parking brake
2. Place wheel chocks behind rear wheels
3. Allow exhaust system to cool completely (minimum 2 hours after last operation)
4. Apply penetrating oil to all exhaust fasteners, clamps, and oxygen sensor threads
5. Raise vehicle using floor jack and support securely on jack stands at frame points
6. Verify vehicle is stable before working underneath

Procedure

1. 1

   Locate and identify flex pipe assembly
   Position yourself under the vehicle near the transmission crossmember area. The flex pipe is located in the mid-section of the exhaust system, between the catalytic converters (near firewall) and the muffler assembly. Identify the upstream and downstream oxygen sensors on either side of the flex pipe section. Note the orientation and routing of exhaust hangers.
2. 2

   Disconnect upstream oxygen sensor
   Locate the upstream oxygen sensor electrical connector near the transmission tunnel. Press the connector release tab and carefully disconnect the wiring harness. Using an oxygen sensor socket, carefully loosen the sensor by turning counterclockwise. Remove the sensor completely and set aside in a clean area away from contaminants. Do not allow sensor to hang by its wire.
   ⚠Do not use excessive force on oxygen sensor. If sensor does not turn easily, apply more penetrating oil and wait. Damaged threads will require catalytic converter replacement.
3. 3

   Disconnect downstream oxygen sensor
   Locate the downstream oxygen sensor on the outlet side of the flex pipe assembly. Disconnect the electrical connector by pressing the release tab. Using the oxygen sensor socket, carefully remove the sensor by turning counterclockwise. Store the sensor in a clean location with threads facing upward to prevent contamination.
   ⚠Keep oxygen sensors away from any fluids, oils, or debris. Contamination will damage the sensor and require replacement.
4. 4

   Support exhaust system
   Place a jack or support stand under the muffler section to support the weight of the downstream exhaust components. Adjust height so there is no strain on the exhaust hangers but the system is adequately supported. This prevents the exhaust from dropping when the flex pipe is disconnected.
5. 5

   Remove upstream flange bolts
   Locate the flange connection between the catalytic converter outlet and the flex pipe inlet. There are typically two bolts securing this flange. Using a socket wrench, remove both flange bolts. If bolts are seized, apply additional penetrating oil and allow to soak. Remove the old flange gasket and inspect the mating surfaces for damage.
   ℹ️Bolts may be corroded. If bolts break during removal, the flange studs may need extraction or replacement.
6. 6

   Remove downstream connection
   At the downstream end of the flex pipe, remove the exhaust clamp or flange bolts connecting the flex pipe to the intermediate pipe. If equipped with a band clamp, loosen the clamp bolt completely and slide the clamp away from the joint. If equipped with a flange, remove both bolts and separate the connection. Remove any gaskets or seals.
   Torque spec

   Exhaust Clamps55 Nm (41 lb-ft)

   Flange Bolts45 Nm (33 lb-ft)
7. 7

   Remove exhaust hangers
   The flex pipe assembly is typically supported by one or two rubber exhaust hangers. Using an exhaust hanger removal tool or careful prying with a pry bar, detach the metal hanger loops from the rubber isolators. Work carefully to avoid tearing the rubber hangers if they will be reused. Note the orientation for reinstallation.
8. 8

   Remove flex pipe assembly
   With all connections and hangers disconnected, carefully lower and maneuver the flex pipe assembly out from under the vehicle. The assembly may need to be rotated or angled to clear the frame rails, driveshaft, and other components. Inspect the removed assembly to confirm proper replacement part selection.
9. 9

   Clean mating surfaces
   Using a wire brush, thoroughly clean all flange mating surfaces on both the catalytic converter outlet and the intermediate pipe. Remove all old gasket material, carbon deposits, and rust. Clean the oxygen sensor bungs with a thread chaser or tap if available. Inspect all surfaces for cracks or damage that would affect sealing.
10. 10

    Install new flex pipe assembly
    Position the new flex pipe assembly under the vehicle. Install new flange gaskets on both upstream and downstream connections. Maneuver the flex pipe into position, aligning the flange bolt holes. Attach the exhaust hangers to the rubber isolators, ensuring proper orientation. Do not fully tighten any fasteners yet.
    ℹ️Ensure flex pipe is oriented correctly with proper clearance from driveshaft, fuel lines, and brake lines before tightening.
11. 11

    Install upstream flange connection
    At the catalytic converter outlet, ensure the flange gasket is properly seated. Install the flange bolts finger-tight. Using a torque wrench, tighten the bolts in a cross pattern to the specified torque. Verify the flange is seated evenly with no gaps.
    Torque spec

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

    Install downstream connection
    At the downstream connection to the intermediate pipe, install the new gasket if using a flange connection, or position the slip joint properly if using a clamp. Install flange bolts or exhaust clamp. Tighten flange bolts to specification using a cross pattern, or tighten the clamp bolt to specification ensuring even compression around the joint.
    Torque spec

    Flange Bolts45 Nm (33 lb-ft)

    Exhaust Clamps55 Nm (41 lb-ft)
13. 13

    Reinstall upstream oxygen sensor
    Apply a small amount of anti-seize compound to the oxygen sensor threads (avoid getting any on the sensor tip). Thread the upstream oxygen sensor into the catalytic converter bung by hand until seated. Using the oxygen sensor socket and torque wrench, tighten to specification. Reconnect the electrical connector ensuring it clicks into place securely.
    ⚠Do not over-tighten oxygen sensors. Excessive torque can damage the sensor or exhaust bung threads. Use a torque wrench.
    Torque spec

    O2 Sensor55 Nm (40 lb-ft)
14. 14

    Reinstall downstream oxygen sensor
    Apply anti-seize compound to the downstream oxygen sensor threads (keeping compound away from sensor tip). Install the sensor by hand into the flex pipe or intermediate pipe bung. Tighten to specification using a torque wrench and oxygen sensor socket. Reconnect the electrical connector and ensure it is fully seated.
    Torque spec

    O2 Sensor55 Nm (40 lb-ft)
15. 15

    Final inspection and clearance check
    Remove the support from under the exhaust system. Visually inspect all connections for proper alignment and torque. Verify that the flex pipe and all exhaust components have adequate clearance from the driveshaft, fuel lines, brake lines, chassis components, and body panels. Check that all oxygen sensor wires are properly routed and secured away from heat and moving parts.

Reassembly

1. Verify all exhaust clamps and flange bolts are torqued to specification
2. Confirm all oxygen sensor electrical connectors are fully seated and locked
3. Check that exhaust hangers are properly engaged in rubber isolators
4. Ensure no tools or parts were left in the work area

Verification

• Lower vehicle from jack stands to ground level
• Start engine and allow to idle. Listen for any exhaust leaks at the flex pipe connections
• With engine running, visually inspect all joints for exhaust gas leakage
• Check oxygen sensor operation: scan for diagnostic trouble codes using an OBD-II scanner. No oxygen sensor codes should be present
• Test drive vehicle and verify normal exhaust sound with no rattles or abnormal noises
• After test drive, re-inspect all connections while exhaust is hot for any signs of leakage
• Verify exhaust maintains proper clearance during suspension travel and acceleration

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