2015-2020 BMW M3 / M4 (F8x) S55 spark plug and ignition coil replacement
Tools
- 3/8 inch drive ratchet with 6 inch and 10 inch extensions
- Torque wrench that covers 5 to 25 ft lbs
- Torque wrench that covers 60 to 300 in lbs
- 14mm thin-wall magnetic spark plug socket
- T25, T30 Torx bits
- 10mm socket
- Small pick set for coil retaining clips
- Compressed air with blow gun (for clearing plug wells)
- Nitrile gloves and shop rags
- Dielectric grease
- Anti-seize (nickel-based, for plug threads only)
Parts
- Spark plugs — NGK 96206 SILZKAR8H8SG (BMW OEM 12120039664), six required
- Ignition coils — BMW 12138616153 (Delphi GN10570 acceptable OE equivalent), six required, replace as a set on any car above 60,000 miles
- Coil harness connectors — inspect, replace individual pigtails only if the locking clip is broken
Steps
01Disconnect the battery
The S55 engine ECU wants to see zero coil activity during plug changes to avoid stored fault codes. Open the trunk, lift the trunk floor, and disconnect the negative battery terminal at the battery in the trunk. Wait five minutes for the DME to power down before touching the coil connectors.
02Remove the engine cover and airbox cover
The center engine cover pulls straight up from four rubber grommet mounts. On F8x M3 and M4, the airbox intake tube blocks direct access to the front cylinders; loosen the two throttle body clamps and lift the intake plenum away without disconnecting the MAF or crankcase breather. Cover the exposed throttle body openings with clean rags. Any debris that falls into an open throttle body will end up in a cylinder; take the extra minute to cover them.
03Disconnect the coil harness connectors
Each coil connector has a wire-bail lock. Lift the bail with a small pick, then rock the connector free by hand. Do not pull on the harness; the S55 coil pigtails harden with heat and the wire will pull out of the terminal at the connector body.
04Remove the coil hold-down bolts and lift the coils
Each coil is retained by a single 10mm bolt at the front edge. Loosen and remove each bolt. Lift the coil straight up out of the spark plug well. Rocking side to side to break free is fine; twisting is not; the boot tears and gets left in the well.
05Blow out the spark plug wells
Fit a blow gun into each empty plug well and blow the debris out with compressed air before removing the plug. Any grit that falls past the plug when the plug comes out ends up in the cylinder. This step matters more on the S55 than on iron-block engines because the aluminum head is soft and sooty debris scores the plug threads.
06Remove the old spark plugs
Fit the 14mm thin-wall magnetic plug socket on a 10 inch extension. Break each plug loose gently. Once free, spin out by hand until the plug can be lifted straight up on the socket magnet. Inspect each plug: normal color is a light tan on the porcelain and a dry electrode. Black soot means rich running (fueling calibration or misfire); white or blistered porcelain means detonation (typically from too-aggressive tune or bad fuel).
07Prep and install the new plugs
Confirm the new plug gap on each new plug with a wire gauge; the S55 spec is 0.028 inch (0.7 mm) and NGK ships pre-gapped, but a bench check catches the occasional bent electrode. Apply a small dab of nickel-based anti-seize to the plug threads only (not the ceramic, not the electrode). Thread each plug in by hand until fully seated. Torque the S55 spark plugs to 17 ft lbs (23 Nm). Verify against your service manual. Do not over-torque; the aluminum head threads are the failure point, not the plug.
08Install new ignition coils
Apply a light film of dielectric grease inside each new coil boot. Set each coil into its plug well, orienting the harness connector to the outboard side. Press down firmly until the boot fully seats over the plug's ceramic insulator. Install the 10mm hold-down bolt. Torque the S55 coil bolts to 89 in lbs (10 Nm). Verify against your service manual.
09Reconnect the coil harness
Fit each coil connector to its coil. Push straight down until the wire bail snaps to the locked position. Tug lightly to confirm engagement. A connector that is not fully seated will misfire under load once the harness heats up.
10Reinstall the airbox intake and covers
Remove the throttle body covers. Refit the airbox intake plenum. Torque the intake plenum clamps to 62 in lbs (7 Nm). Verify against your service manual. Snap the engine cover onto its grommets.
11Reconnect the battery and clear codes
Reconnect the negative battery terminal in the trunk. Turn the ignition on without cranking for 30 seconds to allow the DME to complete its power-on self test. Start the engine. Idle should stabilize within five seconds with no roughness and no misfire lamp. Scan for stored codes with a BMW-capable tool (Bimmerlink, ISTA+, or Autel MS906) and clear any residual codes from the battery disconnect and coil-out state.
Notes
Reference guide — verify every torque figure before you rely on it. A general procedure compiled by Wrenchpit, not a first-hand write-up from one owner's vehicle. The fastener torques below are commonly cited values, not measured ones, and they vary by model year, engine and trim. This job involves fasteners where an incorrect torque can let a component come apart in service. Look the figures up in your service manual and use a calibrated torque wrench. Part numbers should be checked against the labels on your old parts.
Applies to roughly 2015-2020 model years. Filed under 2016 because a guide carries a single model year.
The S55 3.0L twin-turbo inline six shipped in the F8x M3, M4, and M2 Competition. Factory recommendation on plugs is every 60,000 miles, but the community consensus (m3post, m3-forum, BimmerBoost) is 20,000 to 30,000 miles for tuned cars and every plug service for track cars. High-boost tunes push cylinder pressures well beyond stock and wear the electrode fast. NGK 96206 is the OEM plug in the correct heat range for a stock S55; going one step colder (NGK 97506) is common on Stage 2+ tunes running 20+ psi. Coils on the S55 have a well-known failure pattern that starts around 40,000 miles with intermittent misfires under boost on one or two cylinders. Replace as a full set of six once one goes; mixed old-and-new coils cause phantom misfire chases. Inspect the CCV valve on the valve cover any time the coils come off; a stuck CCV pulls oil into the intake and coats the plug electrodes with a black wet film that reads like a coil failure. Buy plugs and coils from a BMW authorized parts network; the S55 plug is a widely counterfeited part and fake plugs run rich and misfire under boost.
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