My cat clogged last winter and was changed figuring that after 140K it was 'due'. But now its fall and 8K later I need another one. Last time everything scanned fine, spark plug looked clean... blah blah.

I haven't scanned it yet but nothing has changed mileage or feel wise so I don't expect to find anything out of range but I think something must be out of whack. Any ideas on what to try blind so to speak?

 

Bump, someone must be able to tell me where to start looking. Don't exactly want to send my car to GM without a 'list' of things to diag. They are likely to check my tire pressure as a cause otherwise

 

Generally killing cats prematurely is caused by a rich condition. Have you done anything that would affect that? Programming, etc? Might check for an exhaust leak or bad O2??? Do you or have you run any leaded gas or additives? What brand of cat did they install?

If the car feels/runs fine, what leads you to believe you need a new cat?

 

just a quick question, how did u know ur cat needed changing on both occasions? thanks

 

Turns out the car is fine, well except for the cat.

The first time, the cat's core melted down preventing the motor from going above 1400RPMish and this time I heard a rattle that I thought was the tranny crossmember or mount but ended up being that the cat's internal core is breaking up.

Everything scans out ok, and passes visual inspection though so no worries... for now. Probably just bottomed out hard on a speed bump and shattered the core this time around.