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2005 PSM 2.5RS
37 Posts
Discussion Starter #1
I'm having issues with engine knock that I just cannot diagnose in my '05 2.5RS 5MT. Engine is bone stock with 70k miles.

I couldn't hear any knock, but IAMs were around 0.1 or 0.2 and I've done everything in the book to eliminate any possible source of mechanical noise (remove heat shields etc.) That didn't help so I tried tuning it by retarding timing (tactrix cable). This was somewhat successful for WOT pulls and I got the IAMs up slightly. Still showed bad knock driving around town.

Now I've completely rebuilt the entire top end of the engine. Absolutely no change except I put in all Group-N mounts and now I can hear it knocking from inside the car.

These are the compression numbers after the rebuild:
Cylinder #1 210psi
Cylinder #2 210psi
Cylinder #3 210psi
Cylinder #4 200psi

They seem a little high but it may just be the calibration of my tester.

What in the world could be causing a perfectly good engine to knock? It's most severe when taking off from a standstill or when cruising and then accelerating without downshifting. I can't hear any knocking under engine braking, so it's definitely of the detonation variety, not rod knock.
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