RomRaider

Welp, did I leakdown test. Cylinder 2 has ~30% leadage and is very clearly coming from the exhaust. Didn't hear anything from the oil neck and no bubbles in coolant expansion tank. Forgot to check pcv. So my guess is either burnt exhaust valve or blown headgasket leaking air into cylinder 4?

sounds like the heads coming off for a nosey then see what's happened

So the test was user error. I didn't notice the air pressure was moving the piston down slightly and opening the valves. However, I finally got around to looking at the Forester again today and I noticed a faint knock I didn't notice before at certain a rpm range. Put a brick on the pedal and went to listen under the hood. Sounds like rod knock, but is only present around 3k. Any chance it's anything less severe? And just for the sake of completion, that's probably what's screwing up my tune, correct? Knock sensor is hearing that and making the changes seen in my logs?

https://imgur.com/a/Mm9qDjN

are you sure that's not a valve clattering in that video? always harder to tell vs listening in person. What you could try is moving the phone around to different areas of the engine bay and see if the sound changes any on the recording. But yes if the ecu is hearing knock then it will pull timing that's all it can do.

I'm definitely not 100% sure on the origin of the noise. It's possible it's valve clatter, but it's pretty loud and seems to originate from the block just below the throttle body. I don't think it's piston slap since it doesn't seem to change when the engine is warm.