Spark Plug replacement on a Subaru Impreza STi/WRX

Installing the coils (Step 6)

This is just like steps 3. Line the coil back over the spark plug and re-install the bolt. Remember on the left rear side (facing car) there is the bracket that needs to connect with the coils bolt. Each coil must connect to it’s spark plug. The coils with the shorter wires go to the spark plugs closer to the firewall. Even though when removing these, it felt like they had a clip holding them in, THEY DO NOT CLIP BACK IN, they just seat there and you tighten them down

Re-install battery, washer resevoir, and intake (Step 7)

If you forgot how to do this look at the pictures in steps 1 and 2 again.

Your done! Start the car up and go for a ride.

Additional Info:

  • Spark Plugs Used: Denso Ultra-Fine 0.4mm Iridium Spark Plugs, part# IKH22. These are one step colder over the stock spark plugs
  • Price: Around $50 bucks
  • Gapping: These spark plugs DO NOT need to be gapped at all. They come pre-gapped for the STI. Just put them in and tighten them down.
 Torque Settings:
  • Tightening torque (spark plug): 21 N·m (2.1 kgf-m, 15.2 ft-lb)
  • Tightening torque (coil): 16 N·m (1.6 kgf-m, 11.7 ft-lb)
  • If a torque wrench is not available, tighten the spark plug until gasket contacts cylinder head: then tighten further 1/4 to 1/2 turns.