exhaust

Flex Pipe

for 2021 Ford F-150 3.5L V6 EcoBoost · 4WD

Difficulty

Moderate

Time

1.8 h

Tools

Steps

This procedure covers removal and replacement of the flex pipe section in the exhaust system on a 2021-2024 Ford F-150 with the 3.5L EcoBoost V6 engine.

Warnings

⚠️Exhaust system operates at extremely high temperatures. Allow at least 2 hours cooling time before starting work to prevent severe burns.

⚠Exhaust components may be corroded and fragile. Use penetrating oil 24 hours before beginning work if possible.

⚠Support the exhaust system properly during removal to prevent damage to catalytic converters and O2 sensors.

ℹ️The flex pipe is located between the catalytic converters and the mid-pipe section on RWD models.

Tools required

Floor jack and jack standsEssential

Wheel chocksEssential

Torque wrench (10-80 Nm range)Essential

15mm socket and ratchetEssential

13mm socket and ratchetEssential

18mm wrench or socketEssential

O2 sensor socket (22mm)

Penetrating oil

Wire brush

Exhaust hanger removal tool

Anti-seize compoundEssential

Safety glassesEssential

Work glovesEssential

Parts

Flex pipe assembly × 1 — Use OEM Ford specification
Exhaust flange gasket (upstream) × 1 — Use OEM specification
Exhaust flange gasket (downstream) × 1 — Use OEM specification
Flange bolts and nuts × 6 — M10 exhaust hardware
Anti-seize compound × 1 — High temperature rated

Preparation

Park vehicle on level surface and apply parking brake
Place wheel chocks behind rear wheels
Ensure exhaust system is completely cool to the touch
Spray all exhaust flange bolts, clamps, and hanger bolts with penetrating oil
Raise front of vehicle and secure on jack stands at frame rails
Inspect the flex pipe location - positioned approximately 24-30 inches rearward of the catalytic converters on RWD models

Procedure

1
Remove heat shields if equipped
Locate and remove any heat shields covering the flex pipe area. Remove the mounting bolts and set shields aside. Note the orientation and position for reinstallation.
Torque spec
Heat Shield Bolts16 Nm (12 lb-ft)
2
Disconnect upstream O2 sensor connector
Locate the oxygen sensor downstream of the catalytic converter and upstream of the flex pipe. Disconnect the electrical connector by pressing the release tab. Tuck the wiring harness safely away from the work area.
⚠Do not pull on the sensor wires directly; always disconnect at the connector body to prevent wire damage.
3
Support exhaust system
Place a jack stand or transmission jack under the mid-pipe section behind the flex pipe to support the weight of the exhaust system during removal. Adjust to just make contact without applying upward pressure.
⚠Proper support prevents stress on catalytic converters and other exhaust components during flex pipe removal.
4
Remove exhaust hanger connections
Locate the rubber exhaust hangers supporting the mid-pipe section near the flex pipe. Use an exhaust hanger removal tool or carefully pry the rubber hangers off their mounting studs. You may need to support and manipulate the exhaust slightly to relieve tension.
Torque spec
Hanger Bolts23 Nm (17 lb-ft)
5
Remove upstream flange connection
Locate the bolted flange connection between the catalytic converter outlet pipe and the flex pipe inlet. Remove all flange bolts using a 15mm socket. You may need to use a combination of socket and wrench if bolts spin. Wire brush the studs and apply penetrating oil if they are seized.
⚠If bolts are severely corroded and break, you may need to drill out studs and use new hardware.
Torque spec
Flange Bolts45 Nm (33 lb-ft)
6
Remove downstream flange or clamp connection
Locate the connection between the flex pipe outlet and the mid-pipe. This may be a bolted flange or band clamp depending on configuration. If flange, remove all bolts. If band clamp, loosen clamp bolt and remove clamp assembly completely.
Torque spec
Flange Bolts45 Nm (33 lb-ft)
Exhaust Clamps55 Nm (41 lb-ft)
7
Remove flex pipe assembly
With both connections freed, carefully lower and remove the flex pipe section from the vehicle. You may need to rotate and angle it to clear surrounding components. Inspect the old flex pipe for the failure point to confirm diagnosis.
ℹ️Flex pipes commonly fail due to cracking in the corrugated section or at the welds connecting it to the straight pipe sections.
8
Clean mating surfaces
Use a wire brush to thoroughly clean all flange mating surfaces on both the upstream catalytic converter outlet and downstream mid-pipe inlet. Remove all old gasket material, carbon buildup, and corrosion to ensure proper sealing. Clean the flange bolt threads and inspect for damage.
ℹ️Proper surface preparation prevents exhaust leaks and ensures accurate torque values during reassembly.
9
Install new flex pipe assembly
Position the new flex pipe assembly into place, aligning it with both the upstream and downstream connections. Install new exhaust gaskets at both flange locations. Start all flange bolts or clamp hardware by hand before tightening any fasteners. Ensure the flex pipe is properly oriented with adequate clearance from chassis components, fuel lines, and brake lines.
⚠Verify minimum 1 inch clearance between flex pipe and all chassis components, fuel lines, and brake lines to prevent contact during engine movement and temperature expansion.
10
Torque upstream flange connection
Apply anti-seize compound to the flange bolt threads. Torque the upstream flange bolts in a crisscross pattern to ensure even gasket compression and proper sealing.
Torque spec
Flange Bolts45 Nm (33 lb-ft)
11
Torque downstream connection
Apply anti-seize to fastener threads. Torque the downstream flange bolts in a crisscross pattern, or torque the band clamp bolt if equipped with clamp-style connection. Ensure even gap around the flange perimeter.
Torque spec
Flange Bolts45 Nm (33 lb-ft)
Exhaust Clamps55 Nm (41 lb-ft)
12
Reinstall exhaust hangers
Reconnect the rubber exhaust hangers to their mounting studs. You may need to use a pry bar or hanger tool to stretch the rubber onto the studs. Ensure all hangers are fully seated and the exhaust system hangs naturally without binding or excessive tension.
Torque spec
Hanger Bolts23 Nm (17 lb-ft)
13
Reconnect O2 sensor
Reconnect the oxygen sensor electrical connector, ensuring it clicks securely into place. Verify the wiring is routed away from hot exhaust components and has no contact points that could cause abrasion.
ℹ️If O2 sensor was removed during the procedure, apply anti-seize to threads and torque to specification before reconnecting.
14
Reinstall heat shields
Reinstall any heat shields removed during disassembly in their original positions. Ensure shields do not contact the flex pipe or create interference.
Torque spec
Heat Shield Bolts16 Nm (12 lb-ft)

Reassembly

Remove jack stands supporting the exhaust system
Visually verify all connections are secure and properly torqued
Check that exhaust system hangs evenly with adequate clearance from chassis, fuel lines, and brake lines
Lower vehicle to ground

Verification

Start engine and allow to idle - listen for exhaust leaks at both flange connections
With engine at idle, carefully inspect all connections for escaping exhaust gases (visible as wisps or pulsing air)
Rev engine to 2000 RPM briefly and recheck for leaks
Verify no contact between flex pipe and chassis components during engine movement
Check for proper clearance while assistant turns steering wheel lock-to-lock with engine running
Test drive vehicle and listen for any exhaust noise, rattles, or vibrations
After test drive, re-inspect all connections while exhaust is hot to verify no leaks developed
Check for exhaust odor in cabin during operation which would indicate a leak