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07 Subaru WRX false knock

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I got a WRX that is showing a ton of Knock but unable to hear it in my knock ears. 07 WRX with Cobb AP, Cobb SF, Mishimoto Top Mount Intercooler, Perrin AOS, Perrin light weight crank pulley and Catted down pipe and exhaust system. On a road test it shows up to -10 on feed back knock. The tune is Cobb stage 1 ACN 91, EBCS low wastegate. We have tired a different fuel and added a bottle of VP octane booster. We compression tested the engine and it's 140 to 145 between all cylinders.

We have removed the light weight crank pulley and put a stock one back on. Replaced the knock sensor and checked sensor mounting. No codes set while driving and engine runs smooth, no cylinder misfires seen.

Just wondering if anyone has chased false knock in a Subaru and what did you find? Have a log file aswell.

Attached Files

90 percent of the times it's clutch making that noise...

Dave, sorry to say you have an AVCS issue. You're 25 or so degrees off at one point in your short log between banks and that's severe.

This is usually caused by debris from engine bearings getting into the AVCS pre filter, solenoid and gear. Engine bearing damage generally causes extreme knock at light throttle as your log shows, but I'm not saying that's certainly the cause. I really hope it's not.

Nevertheless, based on the AVCS and knock behavior, I'd inspect the oil filter and do an oil analysis when your next oil change is due. If you buy or borrow an aircraft oil filter inspection tool you can get the filter open without introducing debris and see what it has caught to potentially get some idea of what's going on inside your engine.

In the meantime, check battery terminal connections to ensure they're free of rot and all the way down at the bottom of the posts, not sitting up towards the top where they make poor contact because they're tapered. Do a grounding kit if you haven't already. I have seen major issues like this caused simply by poor grounding which occurs when these cars get as old as yours.

And just to be clear this is a normal EJ255, not a 2.5 that 2 liter heads ended up in the car for some reason at some point?

Let us know what you find. Fingers crossed.

I agree with Mike, I even made an adapter (modified banjo bolt) to check oil pressure at the AVCS Solenoid themselves and when the oil pre-filter is clogged the oil pressure is very erratic and AVCS is lagging behind or simply not working.

Attached is a picture of pretty bad pre-filter that was propably installed with a hammer!

Attached Files

Thanks guys, I saw the drift in the AVCS and was wondering if that could cause my issue. Car is new to the customer and unsure about the maintenance of the enigine and if the filters are still there or not for the AVCS. I did clean on the grounds on the engine but I will build a few extra if the knock continues after dealing with the AVCS.

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