I think I know the answer... second opinions?

[Dalee1104]

Hey all, so I'll preface by saying this isn't technically for a legacy but as I'm sure you guys are all aware the engines are shared amongst subarus. If not okay please remove this topic. 

Anywhos, the car in question is a 2001 subaru forester. The previous owner mentioned it has an engine swap from a 2003 subaru outback, intake manifold is still from the forester and whatnot. I'm pretty sure the engine is the same? I got this car for free in exchange for some work, the body is clean, interior is clean, but has a blown 5 speed and the engine has a cylinder 4 misfire. Runs okay, has a uneven idle, a little lumpy, but does still run and drive with no flashing of the engine light.

The trans I already have squared away, picking one up this Saturday and going to stuff it in but the engine is more worrisome. I went ahead and did spark plugs and plug wires and when I pulled the cylinder 4 spark plug out the plug was huge. Turns out, it's a spark plug repair kit you can buy at autozone. The cylinder head had been stripped, and the repair kit taps new threads in and uses red loctite to secure a new fitting for the spark plug to thread into.

I'm trying to get second opinions on what I should do. I was thinking about doing a leakdown/compression test to see if I'm losing pressure through that plug. Do any of you guys have any experience with these spark plug repair kits? Do they actually work? Am I most likely losing compression on that cylinder causing the misfire? Could the misfire be caused by something else like a coilpack (figured if that was bad id see misfires on all cylinders as its one unit, not coil on plug)? 

I'm leaning towards the only real way to tell is a compression test or leak down and I will likely chase that. I'm predicting I'm going to have to tear the engine down and replace the cylinder head. I was really hoping it would be something smaller but alas that's the way it goes, so I'm trying to be prepared for whatever the situation is. 

I greatly appreciate any insight yall can provide! 

[m sprank]

Leak down to confirm. But sounds like you need a new head and a possibly a rebuild at the same time. 

[Dalee1104]

That's what I feared lol but it's what I was expecting as well. Appreciate it Sprank

[silverton]

the coil packs on those are waste spark so when you have a failure it affects two cylinders, as the paired cylinders fire together.  1 and 2, or 3 and 4

 

You could be losing compression through a bad thread fix and would cause an occasional misfire, like sprank said... your best bet is finding a good set of heads to put on it.

Edited April 7, 2023 by silverton

[Dalee1104]

Yeah more and more evidence pointing towards just needing a new head in whole. What a pain I was hoping for an easy fix lol