Spark Plug Change Help

Attempted doing my spark plugs yesterday. Worked off the Service Manual, and was using new NGK plugs listed in the service manual (everything torque’d to spec etc). Long story short, got things hooked back up and put back together, waited 10 seconds after connecting the ground, the 10 seconds after putting the key in and turning to on. Then I started the engine. Immediately heard knocking, horrible idle, and when I put the car in reverse it was misfiring bad. Check Engine light came on and I turned the car off. T’was a school night, so I bit the bullet and just put the old plugs back in. Car runs better, but still misfires when accelerating, and occasionally puts on the check engine light.

 

Today as I thought about it- there are a few things that could’ve gone awry as I did the exchange initially:

 

Used WD40 (small amount) on the connectors to the coil to the engine harness. (Possibly some ended up inside the connector? – Might spray those connectors out with electronics cleaner.

 

Accidentally disconnected the battery backwards (neg first then positive, with the battery sensor still connected) Could this fry the ECM?

 

Sprayed out the MAF with MAF cleaner. (small spritz held can back good 15”)

 

Ignition coil packs perhaps aren’t fully seated on plugs? (I pushed and twisted them as far as I could get them to go. Bolted in to torque spec 5.9 ftlb)

 

Also replaced the battery for a Napa Legend Premium, and engine air filter to Fram. I changed the filter back to the stock one after the engine ran poorly, but kept the new battery in.

 

 

 

I also didn’t know if the ECM just needs time to recalibrate after the change. If so how long? 1 day, 2 days? I would think it should even out after 30 minutes or so of driving time.

 

I’m going to try to pull the check engine codes and see what it says.

 

The car was driving fine before the maintenance. Seems there are four elements: plug, coil, wiring harness and ECM.

 

Any input/tips/checks would be greatly appreciated.

 

Thanks.

 

FIXED! UPDATE: Turns out plug insulators were breaking when I put the plugs in and then causing misfires. I blamed the magnetic 14mm plug socket I got from O'Reilley. Won't be using a magnetic plug socket again. Additionally, the NGK 93482 (non-subaru version) were gapped wrong (off .1mm). Took those back. Got Subaru plugs from dealer, a normal 14mm plug socket, and a stock Subaru Air Filter. I also sprayed the coil connectors out with CRC QD electronics cleaner and let them dry overnight.

 

I used HVAC silver tape to keep the 1" extension and plug socket together as I installed the new ones, and removed the socket very carefully.

 

Glad to put this beast to sleep (hoping I didn't do long-term damage when I drove the car misfiring).

Edited November 9, 2019 by Lttlwing16

Maybe you had the wired crosses with the new plugs and corrected their position when you installed the olds plugs. YouTube crossed spark plug wires to see if you had a similar issue

 

I doubt the other work contributed to your issue because the old plugs worked fine.

 

Compare the gaps between the old and new plugs, if the are the same then return and get a new set

 

Damn that sucks, and least your getting a great lesson in patience building changing plug after plug along with hardened knuckles

 

Are you changing them out on a 6 cylinder

Its the WD40 dude. Get that stuff out of there pronto. Pretty sure it doesnt say that in the manual

when you do your plugs

 

 

1. do them one at a time

2. do not use anything other recommended Subaru products as lubricants/cleaners...

 

 

I did the plugs on my 5th gen and I did straight iridium, no not paying $18 a plug for iridium that have a lop on the end of the ground. There is absolutely no difference in how the car runs or fuel economy...

Edited November 8, 2019 by YeuEmMaiMai

Its the WD40 dude. Get that stuff out of there pronto. Pretty sure it doesnt say that in the manual

 

*Facepalm* you're completely right. I saw the tip from a 1a autoparts repair video, and the connectors were stuck tight so I figured just a drop while the connector is connected wouldn't hurt. Put it on there Weds , probably can spray them off tonight/tomorrow. Can I use MAF cleaner on the connections, or do I need to use actual electronics cleaner?

 

Possible it did long term damage?

If you need to put anything on the connectors use something called die-electric grease. Comes in a tube, much safer than wd40 for high voltage and electronic components. MAF cleaner is fine to wash it out, but make sure it dries out completely before reconnecting.

If you need to put anything on the connectors use something called die-electric grease. Comes in a tube, much safer than wd40 for high voltage and electronic components. MAF cleaner is fine to wash it out, but make sure it dries out completely before reconnecting.

 

Will attempt to wash them out tonight. Hopefully that's the issue. I'll also try to fully seat the ignition coil packs on the coils. Could also be part of the issue. Damn things are hard to get fully seated.

You didn't reverse the coils right? Black on back IIRC.

You didn't reverse the coils right? Black on back IIRC.

 

Not likely, worked one plug/coil at a time

Updated OP with fix

Interesting, I wonder how the insulators broke? I'd be curious to see a picture because I don't really understand.

 

Also, anytime I've used ngk plugs, the gap has been off by like .1mm. It's not a big deal though, it's not enough to make any difference, I never touch them. I kind of wonder if ngk does that on purpose, because the gap will grow as the plug wears/ages. Either way, it's always been within the .039-043" gap that Subaru specs for my 09, I think that's the range, I'm going off memory.

Interesting, I wonder how the insulators broke? I'd be curious to see a picture because I don't really understand.

 

Also, anytime I've used ngk plugs, the gap has been off by like .1mm. It's not a big deal though, it's not enough to make any difference, I never touch them. I kind of wonder if ngk does that on purpose, because the gap will grow as the plug wears/ages. Either way, it's always been within the .039-043" gap that Subaru specs for my 09, I think that's the range, I'm going off memory.

 

Yeah, it's weird. The ceramic insulators broke on both the new (NGK) plugs I put in and the old ones I put back in. I think what was happening was the magnetic plug socket was attracted to the end of the plug, which caused the inside metal of the socket to knock against the ceramic. Additionally, the magnet would pull of the plug as I was installing/changing bits/ratchets. and I'd have to reseat on the plug in the well, where above I think was occuring.

 

Folks from Napa, autozone, pepboys, and the Subaru service techs I spoke to said you don't gap iridium, and .1 is enough to make a difference. *Shoulder shrug*. I didn't even check the subaru branded NGK's (per the Subaru service tech's recommendation), just put them in and they worked.

 

Fingers crossed I don't run into problems down the road from driving around with occasionally misfires.

Updated OP with fix

Thanks for following up!