A Step by Step Guide including pictures.
This instruction sheet shows the steps required to change Spark Plugs on a Subaru WRX and STI 2008-2020.
We always recommend that work is carried out by a qualified vehicle technician. Please note this is a fiddly and difficult job mainly due to the lack of space between engine and chassis.
You can buy the Spark plugs required for this job at this link https://scoobyparts.com/subaru-impreza-wrx-sti-performance-parts/spark-plugs-ignition-leads
This is a guide only and we cannot and will not be held responsible for any harm or damage caused to either yourself, others or your vehicle by following this guide. Ensure vehicle ignition is switched off and keys removed prior to commencing work. We strongly recommend also disconnecting the battery prior to commencing work.
This guide is relevant to a 2008-2020 model STI. However many of the steps involved are similar to earlier models back to the 2001 Bugeye WRX models.
Tools Required
Flat Head Screwdriver
Either Subaru’s own specialist tool or a combination of Spark plug socket plus small and medium sized extensions with hex ends and a spanner to fit.
Ratchet
Pliers
12mm Socket or Spanner
10mm Socket or Spanner
Time Expected
1.5-2 hours
Difficulty Level
Medium
Starting on the Drivers Side / Off Side (for RHD Cars). Wait for vehicle to cool down to prevent burning yourself during fitment.
1. Unplug the Mass Air Flow Sensor and the two Airbox clips.
2. Carefully move Pipes and Mass Air Flow wire away from edge of Airbox.
3. Loosen Jubilee clip nearest engine
4. You can now carefully remove the rear half of the Airbox.
5. Remove Panel Air Filter
6. Remove Air Flow Guide by removing the two clips at the front.
7. Undo the two bolts supporting the front half of the Airbox
8. Undo the bottom bolt securing the Airbox in place. You can now carefully remove the Airbox from your Subaru.
9. Using a spanner undo the Coilpacks and slightly twist and move carefully out of the way to gain access to the Spark Plugs.
10. Using either the specialist Subaru Spark Plug Tool or the combination of Spark Plug socket, extension pieces with hex ends and spanner undo the Spark Plug and carefully remove from cylinder.
Remove old Spark Plugs and install new replacements. Refitting is a reversal of this process. When fitting be extremely careful not to damage the Spark Plugs upon refitting. Also check that the Spark Plugs you are fitting are the correct model for your car. They should be the same size and length as those you have removed. Most Spark Plugs come pre-gapped and many cannot be re-gapped.
Passenger Side / Near Side (for RHD Cars)
11. If not already done so, undo the bolt and remove the Negative connection to Battery
12. Undo the two central battery clamp bolts and remove.
13. Undo the bolt and remove the Positive connection to Battery.
14. Remove battery and plastic tray from car.
15. Using pliers undo the clamp securing the hose to the Air Pump.
16. Unclip the two Air Pump loom connections and lift away.
17. Undo the 2 securing bolts and remove Air Pump from car.
18. With the Air Pump removed you can now gain access to the 10mm bolt which holds the pipework. Once undone you can move out of the way the pipework and cover, which allows access to the Coilpacks and then Spark Plugs. Tip – you can use tie-wraps to secure pipework whilst working. Just ensure they are all removed once completed.
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Follow Steps 9 and 10 to remove Coilpacks and Spark Plugs and refit new Spark Plugs. Refitting is reversal of this process. When fitting be extremely careful not to damage the Spark Plugs upon refitting. Also check that the Spark Plugs you are fitting are the correct model for your car. They should be the same size and length as those you have removed. Most Spark Plugs come pre-gapped and many cannot be re-gapped.
You can buy the Spark plugs required for this job at this link https://scoobyparts.com/subaru-impreza-wrx-sti-performance-parts/spark-plugs-ignition-leads