So i finally figured out the rattle in my car. I have a bad cat on the driver's side. I mean I banged on both cats with my fist and only the left one rattled. it sounds like there are a bunch of rocks, or pieces of metal in there. if the cat has too many gas deposits, it means i'm running rich right? I mean I haven't thrown a single code so I have no idea where to start. of course for now, I'm just going to gut the cats.
In the future though I'd like to put on another catalytic converter. that means I gotta fix the problem so I won't keep having to replace it. anybody have any idea where I should start? I've got a CAI and a tune that came with the CAI. So I don't think it's the tune.
What're the usual problems of running rich?

 

Are you sure that it is the cat and not the heat shield or something loose?

If it is the cat for sure then there is an EPA-mandated 8 year/80k mile warranty on catalytic converters. Take it to the dealer and they have to fix it for free.

Hopefully that helps, if not then just post so.

 

Hey guys I've got an 04 gt with the same problem and I have no more ideas for a fix. It's blown the cat out twice now, did you ever find a fix? Any help would be great thanks!

 

I'm pretty sure it's the cat, if not there IS something in my pipes. I've listened all around as I bang on the left cat, and it still rattles. but yeah, I'm just going to straight pipe it. The inspector I go to doesn't check air quality anyway.

 

Put on Bassani hi-flo cats.

 

It is the cat but like I've said mine has done it twice now. The muffler shop isn't warrant mine out anymore because they said they don't just crap out on there own. I just don't know what would cause it.

 

Blown cat could be caused by running too rich. The fact that the tune came with the CAI doesn't mean it's a good tune, where did it come from? Could get your A/F checked at a dyno shop. It's just a theory though, who knows what really caused the failure.