#1 misfire on 97 outback

[jelly man]

I have a 97 outback with an EJ25 that I replaced the head gaskets on just after I bought it. When I had the heads cleaned all the spark plugs looked ok. It now has a low speed misfire after it warms up from idle up to 2k-3k rpm. The onboard diagnostics says it is # 1 cylinder. I replaced all the spark plugs but # 1 because it started to strip out and I didn't dare pull it . The others came out easily with WD40. I swapped # 1 and # 3 injectors and changed the coil and replaced the spark plug wires. It still misfires on # 1 cylinder. I also swapped the plugs on #1 and #3 injectors and still it only misfires on #1 so I don't think it's in the wiring or the computer either. The next step would be to replace the # 1 spark plug but I'll probably wind up having to pull the head and putting in a helicoil. Before I try that can anyone think of any other cause or anything else I can do? I'd sure hate it if I go to all that trouble and it turns out to be something else simple that I hadn't thought of.

[Fairtax4me]

It started to strip as you were removing it? What made you think that?

 

I had a spark plug on my Ranger that worked its way loose once and eventually exhaust started to blow by the seat of the plug. After about two weeks of a cold start misfire it went away, only to come back about a month later as a dead miss. Pulled all the plugs and found one very difficult to remove compared to the rest, it was covered in carbon and part of the seat and threads were literally blown out. But a brand new one threaded into the head no problem, so a new plug and away I went.

[jelly man]

It broke loose as hard as the rest but then it started getting very hard to turn after a turn or so. I sprayed WD40 on it and tried working it back and forth a little then backing it out a few times but that didn't make a difference. I figured some of the aluminum threads were stuck on the plug and it started getting harder to turn the more I went. I figured I was making a bigger mess of the threads by taking it out so I tightened it back in and hoped for the best. I hit the others with WD40 first. They broke loose hard at first also but after that they could be turned by spinning the extension in your fingers.

[idosubaru]

gah, that sucks. i'd take it out, chase the threads with a spark plug thread chaser and try to install another plug. if it starts to get tight, work it back and forth and take LOTS OF BREAKs. as it gets tight the metal is going to start heating and expanding almost instantly (rub your hands together really hard...they heat up fast). if you take it really slow, work it back and forth and take a bunch of 10 minute breaks you might do little damage and leave enough metal to repair the threads with a chaser. i just helped someone do this on an intake manifold bolt a month ago. trying to remove it in 5 minutes it would have sheared. working it like i said, he got it out in about 30 or 45 minutes and saved the threads. it was so tight i was actually thinking that wouldn't work but i knew that was the only hope and he got lucky.

 

the EJ25's are a real pain with spark plug access. they sell thread repair kits, i'd ask folks if there's anyway to get access to repair the threads? maybe loosen the lower motor mounts and jack the entire engine up, the #1 being up front yo umight be able to get access to it if needed.