So ive been pushing my tC real hard lately and within the last 3 days ive noticed a slight rattle/knock coming from the engine under acceleration only. I opened the hood and listened for knocking at idle and there was nothing. The supercharger still sounds perfectly fine too. Last night on my way home from work the CEL came on. Today i hooked it up to the OBDII computer and read this code:

P0420 Catalyst Efficiency below threshold (bank 1)

I could be wrong but this tells me my cat has an issue. Maybe its plugged up. What do u think? ...and could this be causing a rattle/ knock under acceleration?

 

Likely bad O2 sensor or bad CAT.

http://www.obd-codes.com/p0420

 

Thanks for the link. Well at least that'll be covered under warranty. But my main concern is this knocking noise. Sounds like if u were to accelerate heavily with out letting the car warm up on a below freezing day. Im hopping that it has something to do with the cat being plugged up causing massive backpressure in the manifold causing a knock. And since it only happens under acceleration (when exhaust pressure is greatest esp. With boost) it might make sense. But then again im not a mechanic. Is this possible?

 

I guess it sounds plausible... but the question would be whether it's a plugged/bad cat or a bad O2 sensor. A bad O2 sensor could throw off some other things that could potentially cause some knock too, I guess. I'm no mechanic either... but if you're still under warranty, best to take it in and see what they say.

 

Just brought her in...Worst thing bout keeping your warranty is having bring your car to a dealer. I'd say I have a 17.8% success rate with these service departments but hey If i get through unscathed I will have saved myself a couple of Benjys.

You don't think they're gonna tell me they need to remove the SC in order to get the manifold off? ...That would spell disaster

 

Its the cat... And they gotta take my SC off... There goes my bearings