Change the Spark Plugs on a 2nd Generation (2002-2007 ) GD/GG Subaru Impreza WRX

Works For:
2002, 2003, 2004, 2005, 2006, 2007 Subaru Impreza WRX Models

Source: i-club

Some of the tools necessary for spark plug replacement:

four (4) new spark plugs
3/8″-drive metric socket set
3/8″-drive ratchet (fine tooth works best)
3/8″-drive spark plug socket with integrated u-joint
various length 3/8″-drive extensions
large slotted screwdriver to loosen hose clamps
spark plug gapping gauge and adjustment tool
torque wrench

Factory spark plugs for the 2002 model year WRX is the NGK PFR6G. I used NGK Iridium spark plugs one step colder than the factory plugs, number BKR7EIX.

Note the 16 or 18 gauge electrical wire inserted through the spark plug socket pivot pin for the u-joint. A good spark plug socket has a rubber insert to positively retain the spark plug inside of the socket. Unfortunately, the socket will sometimes get stuck on the spark plug after you install the new one and it pops loose from the ratchet or extension when you pull on it. The wire allows you to simply pull out the socket for easy retrieval. 

This Champion spark plug gapping tool is only good for checking plug gap, not for adjustment (I will upload an image of a decent gapping tool as time permits). Do not pound on the side electrode to close down the gap.

Proper gap as specified by the factory manual is .028″ to .031″. Spark plug gap must be checked prior to installation! I found the plug gaps on an already installed set to be .034″ to .035″, which may cause a high-speed misfire under load.

1) Remove negative battery cable and secure out of the way. Remove the positive battery cable. Loosen the battery hold-down bracket and remove the battery. The coil can be removed without removing the battery but working room is limited and will take longer by doing so.

2) Remove two fasteners securing windshield washer reservoir to driver’s side strut tower. Lift reservoir bottle and unplug wiring harness. Secure reservoir out of the way.

3) Remove two fasteners retaining air cleaner snorkel to radiator support. Carefully wriggle snorkel until it pulls free of the fender panel.

4) Loosen two hose clamps and remove connecting elbow from MAF and airbox assembly. Note position of cables and tubing that clip to the elbow and airbox.

5) Remove two fasteners holding airbox to lower frame rail. Remove airbox either intact or removing cover and filter first. See detailed procedure for air filter element replacement.

6) Ignition coils on passenger-side bank of engine. Each coil is retained by one fastener. On a 2002 WRX, one coil also has a bracket that positions the exhaust gas temperature sensor wire. It is shown in this pic as the gold-colored bracket under the coil fastener.

The coil fasteners will be retained by the coil assembly and will not drop loose when you remove the coil. The coil wiring harness needn’t be removed to replace the spark plugs.

7) Images show the coil fastener and how it is retained, as well as the integrated spark plug boot on the underside of the coil. This entire assembly is easily removed by hand once the fastener is loosened.

8) Remove spark plugs and replace with new ones. Insert spark plug into socket and thread by hand until you are satisfied that it is not cross-threaded, which could become a major headache and time in the shop. Torque to factory specification of 15 ft. lbs. It may be difficult to use a torque wrench in the limited space around the cam cover and using a u-joint adapter will alter torque readings significantly. If that’s the case, tighten snugly and you will be able to feel the spark plug crush washer being compressed against the cylinder head. Tighten them snugly, but 15 ft. lbs. is not a lot. Basically, I tighten them until I feel the crush washer compress and then cinch them down a bit more to make sure it doesn’t back out of the hole. I found two of the old spark plugs to be almost loose enough to be removed by hand!

9) Replace ignition coils by placing boot squarely over spark plug end. You won’t be able to see the spark plug when it is installed but you will feel the boot slide over the spark plug and the coil fastener will line up with its threaded hole.

10) Replace other components, taking care to route vacuum hoses in proper clips on air box cover. Cruise control cable must be routed above the elbow to fit into its retaining clip. Tighten hose clamps on elbow, ensuring that the worm gear of the clamp does not rub on adjacent parts.

11) Start engine and check for proper operation. If it doesn’t idle smoothly, then double-check coil connections.