Catalytic Convertor Problems

[MTomlinson07]

On my Mom's 1999 M3 the catalytic convertor went bad 5 months ago, and was replaced. She opted for the non BMW branded replacement because it was $500 less. 2 months later the catalytic convertor went bad again. She bought the BMW branded one this time. Now this one has gone bad and it has only been three months! The shop that does the work specializes in BMW's and said that it is impossible to have two defective catalytic convertors so there must be some other problem, possibly with the engine. The only code that the computer shows is for the catalytic convertor. Anyone have any experience with a problem like this or have any idea what me going wrong?

[POWER///M]

buy a good one from bmw but instead of puting that on, by a straight pipe with no converter. Gain in horsepower and sounds louder. When it comes time to get it smogged, put in the catalytic converter and your good to go.

[MTomlinson07]

The second replacement cat that went bad was a a BMW one. I don't think my 45 year old mom will go for the sound that comes with the straight pipe. She already complains about the exhaust on my car.

[nukeduster]

running excessively rich will kill your cats prematurely

check your spark plugs

if they are overly carbonized/black you're running rich

[bryan1970]

although it is very unlikely it isn't impossible. there have been times where i have recived bad parts up to 3 times in a row of course they weren't cats but just goes to show that it can happen. but i'd prolly start lookin' at other possibilities for the premature failure too. you could actually test the cats by putting a gas analyzer on the car and find tou if the cats are infact bad. i guess the O2 sensors could possibly casue a problem as they are the sensors that actually check the efficientcy of the cats