H6 knocking at high RPM

Nov 24, 2022
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I have a 2005 Subaru Outback L.L. Bean Edition with an EZ30 in it. Recently I purchased it from a friend after he needed to sell it because it isn’t running right. He went over a gnarly pothole and it started becoming undriveable within 10 mins. It surges and has no power. At one point it was throwing misfire codes for cylinders 2,4,6 and had a code for O2 sensors. I’ve done the following:

Replaced timing chain tensioners, water pump and reclocked the timing. Driver side had chain slap noise when running and starting, noise went away with new tensioners. Driver side timing was off one tooth, assuming lack of tension and pothole mentioned above knocked it loose just enough to jump.

Replaced all 4 O2 sensors, cleaned and tested MAF by un-plugging it while running. Engine died as a result.

Replaced all 6 spark plugs

Oil and coolant change (from pulling rad and doing timing work)

It will start and idle perfectly fine, it’ll rev up in neutral fine up until about 4K rpm at the rev limiter and it’ll start having a knocking/slapping noise which I initially assumed as due to the timing being incorrect but now I’m thinking it’s maybe running lean and pre-detonating. If anybody has any advice or suggestions on what I should test or do that would be very much appreciated by me Currently there’s no check engine lights whatsoever.
Perform a warm compression test and "cylinder leak down" test.
Measure the oil pressure in a warm to hot condition.
Have a spare oil filter ready, remove the old one and open it. Look for any metallic particles.

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