Catty ?'s

Cat converters should almost never go bad, yours going bad twice suggests either another problem, or a shyster mechanic. Take it back to the guy who replaced it. If he starts telling you it's normal, take it somewhere else. If he's any good, he will look for the real cause this time...

What proof do you have that it's "bad"? The catalytic converter is a reactor that changes the composition of your exhaust. There's no way you can tell how well it's working.

When my catty went the first time i felt a difference in the acceleration and rpms. When it first went i couldnt get the car over 70 miles an hr, then 50 mph, then 40, until eventually it was almost non-driveable. I took it to a mechanic who thought it had to do with the fuel filter and put a new one in and told me it was a variety of other problems. I then took it for a 2nd opinion and the mechanic said it was the catty and replaced it and there was no acceleration or rpm problems. Now nearly 2 months later it is having almost the same acceleration problems (it caught at 40 mph and held the other night) and the other night i heard rattling under the hood as i did the first time. This is why i believe its the catty.

Listen to what I'm saying here... Under normal circumstances the cat will almost never go bad. You must have other problems, even if the symptom you are most concerned about is the cat. If it went badthe first time, something caused it. If it is bad again, the problem has not been fixed. It may very well be that you need another new cat, but unless your real problem gets fixed, you will be here again in a few months.