Spark Plugs

Replace all 10 spark plugs on the 8.4L V10 engine, including removal of ignition coils and inspection of plug condition.

Warnings

Tools required

Parts

• Spark plugs × 10 — NGK LFR6A or Champion RC12YC (verify OEM specification)

Preparation

1. Ensure engine is completely cool to the touch (minimum 2 hours after shutdown)
2. Park vehicle on level surface and engage parking brake
3. Open hood and prop securely
4. Verify replacement spark plugs match OEM specification and are gapped correctly (typically 0.040" for this engine)

Procedure

1. 1

   Access ignition coils
   Locate the 10 ignition coil packs mounted directly on the valve covers. The V10 engine has 5 cylinders per bank with coils mounted vertically. Visually inspect for any damaged wiring or cracked coil bodies before proceeding.
2. 2

   Disconnect ignition coil connectors
   Press the locking tab on each ignition coil electrical connector and pull straight up to disconnect. Work on one cylinder at a time to avoid mixing up ignition coil positions. Note that each connector may have a different colored locking tab or wire routing, but all use the same disconnect method.
3. 3

   Remove ignition coil mounting bolts
   Remove the single 8mm mounting bolt from each ignition coil using an 8mm socket and ratchet. Keep bolts organized if working on multiple cylinders at once.
   Torque spec

   Ignition Coil Bolt11 Nm (8 lb-ft)
4. 4

   Extract ignition coils
   Grasp each ignition coil firmly and pull straight up with a slight twisting motion to break the seal. The coil boot seals onto the spark plug and may require moderate force to remove. If a coil is stubborn, gently rock it side-to-side while pulling upward. Do not pry against the coil body as it can crack.
5. 5

   Clean spark plug wells
   Use compressed air or a shop vacuum to remove any debris, oil, or dirt from the spark plug wells before removing the plugs. This is critical to prevent contamination from falling into the cylinders. Inspect for oil pooling in the wells, which may indicate valve cover gasket or coil seal failure.
6. 6

   Remove old spark plugs
   Insert the correct spark plug socket (verify 5/8" vs 9/16"/14mm against the actual plug) with extension onto the spark plug. Turn counterclockwise to loosen, then unthread the plug by hand once loose. Remove the plug completely and inspect the electrode condition, gap wear, and insulator color for signs of engine health issues (proper combustion shows light tan/gray color).
7. 7

   Inspect spark plug threads and cylinder
   Use a flashlight to inspect the spark plug threads in the cylinder head for damage, carbon buildup, or debris. Do not allow any tools or objects to drop into the open cylinder. If threads appear damaged, thread repair will be required before installing new plugs.
8. 8

   Prepare new spark plugs
   Verify each new spark plug is gapped to specification using a gap gauge. Apply a thin coat of anti-seize compound to the threads of each new spark plug, coating 2-3 threads only. Do not apply anti-seize to the electrode end or allow it to contaminate the insulator.
9. 9

   Install new spark plugs
   Carefully thread each new spark plug by hand into the cylinder head, ensuring it threads smoothly without resistance. If resistance is felt, back out and restart to avoid cross-threading. Once hand-tight, use the torque wrench and correct spark plug socket to tighten to specification (reduce spec by ~10-15% when anti-seize is used). The 8.4L V10 uses aluminum cylinder heads.
   Torque spec

   Spark Plug20 Nm (15 lb-ft)
10. 10

    Reinstall ignition coils
    Apply a small amount of dielectric grease to the inside of each ignition coil boot if desired (helps with future removal). Align each coil over its corresponding spark plug and push down firmly until the coil boot seats completely onto the plug. The coil should sit flush against the valve cover mounting surface.
11. 11

    Secure ignition coils
    Install the 8mm mounting bolt for each ignition coil and tighten to specification using a torque wrench. Do not overtighten as the coil mounting points can crack.
    Torque spec

    Ignition Coil Bolt11 Nm (8 lb-ft)
12. 12

    Reconnect electrical connectors
    Push each ignition coil electrical connector straight down onto the coil until the locking tab clicks into place. Gently tug on each connector to verify it is fully seated and locked.

Reassembly

1. Double-check that all 10 ignition coil electrical connectors are fully seated and locked
2. Verify no tools or parts are left in the engine bay
3. Close hood securely

Verification

• Start engine and listen for smooth idle with no misfires or rough running
• Check for any illuminated check engine light or misfire codes
• Allow engine to reach operating temperature and verify smooth acceleration
• Perform a test drive to confirm proper engine performance under load
• After first heat cycle, consider re-checking spark plug torque if concerned about seating (though not typically required with proper initial torque)

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