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installing/replacing spark plugs

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The biggest problem is the clearance to the fenders - it looks as though the engine will have to be raised 2-3" to get a socket on the plugs. If anybody has a way to do it without the lift I'd like to hear about it.
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Good info so far. There are a few tricks if you have not done this job before. I remember cursing a lot the first time I did it. ;)


Here's a few tips:


-Getting the coil packs out of the way can be difficult on the rear two cylinders. Once you've removed the 10mm retaining bolts, you can rotate the coil packs 180 degrees making them slip out more easily. You don't necessarily have to remove the wiring harness from the coil pack -- the wiring harness is a bit fragile so it's less likely to break if you just leave it attached.

-The combo of spark plug socket, u-joint and short extension is just the right length to reach the spark plug and leave room to attach a ratchet. A low-profile ratchet helps give you more room to work.

-Don't over-tighten. The spark plugs thread into fairly soft aluminum. Use the torque specs above or tighten each plug by hand and turn no more than an additional 1/4 to 1/2 turn until firmly seated.

-Some people recommend using anti-seize on the plug threads. NGK advises not to use it. The plugs already have a coating on them to prevent seizing.

Edited by MilesA
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I found that the LH side required that I remove the battery box in addition to the battery. There's six (6) 14mm bolts holding it down. Two (2) on the side of the box required a long handle racketing box end wrench, but I used a regular size wrench with my makeshift breaker bar pipe. This was the hardest part of the replacement for me. Don't forget to lube the spark plug boots. Some of mine where welded on making it difficult to remove the ignition coil without worrying I was going to damage the boots.


Sent from my SM-G920V using Tapatalk

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The factory guide is pretty much spot on, plus you have a 2.5 which is easier than the 3.6. The rear plug on each side is a royal pain to remove with the six cylinder.


The rear plugs? No, no, the plugs are fine. Trying to figure out how the hell to get the coilpack off in the back, then looking like an idiot because you're spending 10 minutes trying to get it back in, haha.

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  • 9 months later...

Just replaced mine this weekend at 109K miles in my 2016 Legacy.

The battery tray mount bolts (you know the two) were the toughest part of the job for me.

I ended up leaving them out as the four remaining are more than adequate to secure it.

Picked this up from Amazon and it was perfect with the extensions I already had on hand.


Ordered new plugs directly from NGK.

Pic shows How they looked next to new one.


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  • 1 year later...

Figured this was as good a place as any to post an update.

2016 Legacy 2.5 Premium 188k miles.

Second spark plug replacement (see previous post for 109k replacement)

I'm glad I left out the two PITA battery tray bolts. Saved a bunch of time and cursing.


Engine was running just fine.

However... Based on my findings (side electrodes were toast), I let these go too long and will replace again at 60k as per the Service Manual scheduled maintenance interval.


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you will need to remove the intake up to the throttle body and this involves unplugging the maf and un-clipping the harness from the air box . disconnect battery first or wait 10 minutes for the car to shut off completely




you will need to unbolt the PS pump reservoir (oops not applicable to 6th gen)

it is recommended you remove the battery for easier access on driver side

you can do it without jacking the engine.




after you have done the above,



1. Start on the front plug passenger side

2. unbolt coil pack and lay aside

3. unbolt rear coil pack and lay aside (due to length it is IMPOSSIBLE to mix them up) if coil pack is not intact or is otherwise damaged, replace


4. insert spark plug socket into hole

5. insert 6in ext into hole and snap it into the spark plug socket, then rotate it until it slides on plug

6. insert ratchet into extension

7. loosen plug

8. remove ratchet from extension

9. use fingers to finish removing plug

10. remove ext with socket and plug attached

11. repeat 2-10 for rear plug


12. separate ext from spark plug socket.

13. insert new plug into socket.

14. Insert socket into hole

15. insert extension into hole and gently press until it locks into spark plugs socket

16. turn extension left a bit so you are not threaded into hole improperly

17 hand tighten plug with fingers

18. put toque wrench/ratchet on ext and tighten to correct specs

19 remove torque wrench from ext.

20. remove ext from hole while still attached to spark plug socket

21. replace coil pack, make sure you hear it POP and then replace bolt and tighten to spec.

22. Repeat steps 12-21 for rear plug



driver side is identical except for you have to un-clip a brake line and the high pressure AC line from the frame rail and move them back slightly so the socket and ext can clear the rail when removing the plugs



when done replace PS pump reservoir and intake tract on passenger side and do not forget to plug in the maf. replace battery on driver side. start car with nothing on and let it relearn idle

Edited by YeuEmMaiMai
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you will need to unbolt the PS pump reservoir



Gen 6 Legacys have electrically boosted power steering: no reservoir.

"If you don't know where you're going, any road will take you there." ~ The Cheshire Cat (Alice in Wonderland)


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