So here is the problem, after running the car on the highway for a while, there is a funky smell, comparable to rotten eggs or sulfur. Now the Cat was just replaced, as a matter of fact the smell only started after they put the new cat on. I think it might be the CO2 sensor, but i am not a mechanic, and i would appreciate any input.
Its probably irrelevant, but its an 83 z28, 305 stock motor.
Thanks

 

Yep, I know what you're talking about, did the same thing when I first got my cat, now it doesn't. I guess it was breaking in.
Either way that egg smell that you smell is just the cat working, it's converting the gas into sulfur dioxide, if I recall correctly.

 

sounds like that new cat is working great. but i would check it for a leak, it just sounds like you are catching the exhaust fumes so maybe the connection is a little loose. i have to get under my car and tighten mine up as well, i just replaced the cat a couple weeks ago with a new one and it has loosened up a little bit to the point i could hear it, which is incredible with the flowmaster.