This procedure covers the removal and replacement of exhaust manifold studs on the 3.5L V6 EcoBoost engine, including extraction of broken studs and installation of new hardware.

Warnings

Tools required

Parts

• Exhaust manifold studs × 12 — Use OEM specification
• Exhaust manifold nuts × 12 — Use OEM specification
• Exhaust manifold gaskets × 2 — Use OEM specification
• Turbocharger inlet gaskets × 2 — Use OEM specification
• O2 sensor anti-seize compound × 1 — Nickel-based anti-seize

Preparation

1. Ensure engine is completely cold (minimum 2 hours after last operation)
2. Disconnect negative battery terminal and wait 5 minutes
3. Raise and support vehicle on jack stands if accessing from below
4. Remove engine cover by pulling upward on clip attachments
5. Apply penetrating oil to all exhaust manifold nuts and O2 sensor threads, allow to soak minimum 30 minutes

Procedure

1. 1

   Remove oxygen sensors
   Disconnect electrical connectors from both upstream oxygen sensors. Using an oxygen sensor socket, carefully remove both O2 sensors from the exhaust manifolds. If sensors are seized, apply heat and additional penetrating oil. Mark sensor locations (left/right bank) for reinstallation.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
2. 2

   Disconnect turbocharger inlet pipes
   Remove the heat shields covering turbocharger connections by removing mounting bolts. Disconnect the turbocharger inlet pipes from both exhaust manifolds by removing the flange bolts. Support pipes to prevent strain on turbocharger connections.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)

   Exhaust Flange Bolts45 Nm (33 lb-ft)
3. 3

   Remove exhaust manifold nuts
   Working from the center outward on each manifold, carefully remove all accessible exhaust manifold nuts using a socket and extension. Note which studs are broken or damaged. If nuts are seized, apply additional penetrating oil and allow to soak, then retry with increased care to avoid breaking additional studs.
   ⚠Do not apply excessive force to seized nuts. Breaking additional studs significantly increases repair time and complexity.
   Torque spec

   Manifold Nuts39 Nm (29 lb-ft)
4. 4

   Remove exhaust manifolds
   With all nuts removed, carefully separate exhaust manifolds from cylinder heads. Manifolds may be stuck due to carbon buildup; use gentle prying at designated lift points only. Remove and discard old manifold gaskets. Inspect manifold mating surfaces for warping or cracks.
5. 5

   Assess broken studs
   Inspect all stud locations and identify broken studs. If stud broke flush or below surface, mark location clearly. If stud protrudes above surface, attempt removal using locking pliers or stud extractor. Clean area around each broken stud thoroughly with wire brush.
6. 6

   Center punch broken studs
   For each broken stud, use a center punch to mark the exact center of the stud remnant. Accurate centering is critical to avoid drilling into threads. Apply cutting oil to marked locations.
   ⚠Accurate center punching is essential. Off-center drilling will damage cylinder head threads and may require helicoil insertion or head replacement.
7. 7

   Drill pilot holes
   Using a small left-hand drill bit (1/8 inch), carefully drill pilot holes in the center of each broken stud to a depth slightly less than stud length. Use low drill speed and frequent cutting oil application. Left-hand rotation may spin out the stud during drilling.
   ⚠️Drilling into aluminum cylinder heads requires constant attention. Metal shavings MUST NOT enter cylinder head ports or coolant passages. Use shop vacuum continuously during drilling.
8. 8

   Extract broken studs
   Progressively increase left-hand drill bit size, staying centered on pilot hole. Continue until stud wall thickness is minimal. Use screw extractor appropriate for remaining stud size. Apply firm downward pressure while turning counterclockwise. If extractor fails, continue drilling with progressively larger left-hand bits until stud can be picked out with magnetic tool.
9. 9

   Clean and chase threads
   Once all studs are removed, thoroughly vacuum cylinder head stud holes to remove all metal shavings. Use M8 x 1.25 thread chaser to clean and verify thread condition in all stud holes. Inspect threads carefully for damage. If threads are damaged, helicoil installation may be required.
   ℹ️Damaged threads must be repaired before proceeding. Helicoil installation adds approximately 1-2 hours to repair time.
10. 10

    Install new exhaust manifold studs
    Apply small amount of anti-seize compound to threads of new exhaust manifold studs (avoid getting anti-seize on stud portion that enters cylinder head). Thread studs into cylinder head by hand until fully seated. Use two nuts locked against each other on stud end to achieve final tightening if needed. Verify all studs are properly seated and perpendicular to mounting surface.
    ℹ️Studs should thread in smoothly by hand. If resistance is encountered, stop and verify thread condition.
11. 11

    Clean manifold mating surfaces
    Thoroughly clean cylinder head exhaust manifold mating surfaces using wire brush or scraper. Remove all old gasket material and carbon deposits. Clean exhaust manifold mating surfaces similarly. Surfaces must be completely clean and flat for proper sealing.
12. 12

    Install exhaust manifolds
    Position new exhaust manifold gaskets on cylinder head studs. Carefully align exhaust manifolds onto studs and seat against gaskets. Install new manifold nuts finger-tight on all studs. Apply anti-seize compound to nut threads before installation.
13. 13

    Torque manifold nuts
    Torque exhaust manifold nuts in sequence from center outward in three progressive stages: first to 15 Nm, then to 29 Nm, and finally to specification. This ensures even loading and proper gasket compression.
    ℹ️Use progressive torque sequence to prevent manifold warping and ensure even gasket compression across all mounting points.
    Torque spec

    Manifold Nuts39 Nm (29 lb-ft)
14. 14

    Reconnect turbocharger inlet pipes
    Install new turbocharger inlet gaskets. Position inlet pipes to manifold flanges and install flange bolts with anti-seize compound as specified. Torque to specification. Reinstall heat shields and torque mounting bolts.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)

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

    Install oxygen sensors
    Apply anti-seize compound to oxygen sensor threads only (avoid getting compound on sensor tip). Install oxygen sensors to correct locations (as marked during removal) and torque to specification. Reconnect electrical connectors ensuring positive engagement.
    ⚠Do not apply anti-seize to oxygen sensor tip. Contamination will cause sensor failure and false readings.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)

Reassembly

1. Reinstall engine cover by pressing down firmly on all clip locations until seated
2. Reconnect negative battery terminal
3. Lower vehicle from jack stands if raised

Verification

• Start engine and listen for exhaust leaks at manifold/head interface - there should be no hissing or ticking sounds
• Allow engine to reach operating temperature and verify no exhaust odors in cabin or engine bay
• Check for exhaust leaks at all flange connections and O2 sensor locations
• Verify no check engine light illumination and scan for O2 sensor codes
• After first heat cycle, re-check manifold nut torque when engine is cold (recommended but not required)
• Monitor for exhaust leaks during first 100 miles of operation

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