The check engine came on this past weekend, and I took it to have the code checked. The mechanic told me that the cat was bad. I need a new cat. What would be a good cat to replace it with? Should I repace it with a factory cat?

Replace it with a cool cat:
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But seriously, this is an ideal time to replace it with a hi-flow cat from Magnaflow.

http://www.car-sound.com/02product/*...cat=Bonneville

Also, I think we should discuss what else was done to your car by the mechanic, if anything. A catalytic converter typically doesn't just "go bad" without some outside influence. In most cases a "bad" cat is a good indicator that you have one or more bad O2 sensors.

Did the mechanic tell you what code # it was?

Willwren is shipping one your way










Off-topic, but Lash started it

Funny stuff in here

I agree with Lash. What STARTED the problem? A code number would be great, as well as knowing how hot your car typically runs, and what fuel mileage you've been getting up until now.

I got code P0420, Catalyst System Efficiency Below Threshold (Bank 1).

My wife drives the car primarily. We tested it after we got it back from having another engine put in.

First fillup we averaged 23mpg. If I push it, I would get 380 per tank.
I don't know what it is now.

I didn't get much reply on tthis, but can someone tell me why the cat fails? I did put a new engine in the car. The new engine came from a 98 Olds 98. They are both 3800 Series II. Are there different cats for each car that has the Series II

Cats can fail for numerous reasons. Running too rich will clog the passages over time. Running too lean will make it run hotter than normal. Burning oil will plug it up fast with residue, as will an intake manifold failure and burning coolant.