First off, this is sorta a common sense thing. Make sure the car is cold. Park it for the night where you plan to do the change and start the next day. You're gonna get personal with your engine for a few hours
I used the NGK SILFR6C11A Spark Plugs
3/8 Plug Socket (with a rubber boot)
1/4 10mm and 12mm deep well
10mm wrench (for one little nut on the airbox)
3/8 U-Joint adapter or 1" 3/8 extension, for rear plugs.
3/8 6" Extension
1/4 or 3/8, 6" extension with 12mm, whatever works.
Small Flat Head Screwdriver for coilpack clips (very carefully pry them up, you can break them easily)
Large Flat Head for intake clamps
Needle Nose Pliers
Start with removing:
The Battery, negative then positive terminals. 10mm socket. Also the battery lockdown that uses 10mm.
The snorkel to the air box, two plastic rivets
The MAF sensor plug
Slide off the power steering pump hose from the air box
Needle nose pliers to remove clip for MAF sensor wire
Remove intake hose from the airbox
Two bolts secure the box, one 10mm wrench towards the headlamp and one at the bottom middle near the engine, 1/4 or 3/8 extension with 10mm.
Alright, you can see the coilpacks. You'll get a good look at them at this time so if you see one where the metal is separating or even the pack is cracked, it'd be a good idea to replace it.
Doesn't look so
bad now, huh? I removed the metal brackets on each side that hold the coilpack wires up. This can be a hindrance and a help at the same time. Not sure which was more. (2) 10mm bolts hold them on.
The packs are held on with 12mm bolts. Used the 1/4 12mm socket to make switching back and forth quick. The bolts thread out forever and ever and ever so get used to hand loosening. Slide the pack straight off. You're gonna use the 6" extension and 3/8 ratchet for the first four plugs closest to the radiator. Bust it loose and after a few cranks, you can hand loosen the plug out. Best to double check that all the gaps are correct on the new plugs before installation. Subaru spec is .38 - .43.
Now, for torquing the plugs, there's two ways. First, hand tighten the plugs in there to avoid crossthreading. Something you really do not
There's torque specs on the NGK site and in the manual but I just crushed the washer, and when it crushed, gave it another 1/2 to 2/3 turn. I didn't have an inch/lb torque wrench handy. Not sure how you'd even get one on the rear ones anyways. I didn't use anti-seize on the plugs. NGK suggests not to as it can lead to over torquing. I didn't have much issue busting loose the old plugs and a few others said they never used anti-seize and haven't had any issues, given the zinc plating on the plugs prevent it. I believe as long as you don't wait 100k miles to change the plugs again, it should be fine.
Some of the coilpacks might give you issue getting them back in. Make sure they're in correctly and snug. I re-attached the packs and connectors as I went. Make sure they *click* back on. (6.6 lb/Ft is the torque specs for the 12mm bolts)
The back ones is where it gets tricky. The packs can only come out one way. It's best to remember this. When you pull them out, twist them a bit more than 90 degrees and lift it out. That's the only way it'll go back in. The first one I was dumbfounded because the pack literally does not fit between the rail and the valve covers unless in the very right spot.
For the plug, you can use the 6" extension and it's best done with a ratchet that falls out easily. There's no room to hit the release button. You could
try using a screwdriver to push the button but, hey, that's up to you. As soon as it's loose, you can use the U-Joint attached to that a lot more easily. The 6" itself will only go so far before bumping the rail. I just left the U-joint on and hand loosened it the rest of the way out. Reverse order, plug, plug socket and U-Joint, hand tighten it for days and days and days, then once the washer is against the wall, switch to the 6" extension to tighten it down.
that all the packs are bolted down, packs connected, wire brackets in place and reverse order the air box and battery back together. Make sure MAF sensor connector is secure before battery is connected. I took the liberty of cleaning the MAF since it was out anyways and glanced at the filter. Take account for all tools.
Start her up and let her idle for a minute to re-learn, then take a brief drive around for ~10 minutes or so and the IAM should return to normal. If you have RomRaider or some other monitoring software, check for misfires and make sure everything looks good.
Overall, it wasn't nearly as bad as I thought. If it had been 70F out, had a constant supply of cold water, I might actually enjoyed it.
I hope this helps fellow future 3.6 plug changers.
Also should note, I laid plugs out in relation to the engine. 1-3-5 is the passenger side, 1 being closest to the radiator. 2-4-6 for driver side. 2 closest to the radiator. Take a pic for easy reference later.