Stupid Question: How do you tell if a cat conv has gone bad?
 

Short of failing an emissions test after waiting in line for 45 mins and dishing out $15, how do you know it is time for a new cat?

I think they plug before they go bad, you may try bumping this in the morning, Kevin

I believe that the way they are tested is to remove threaded plug and measure pressure being released at that stage, this would indicate a plugged or free-flowing cat. When they go bad they plug up. If your car has been producing normal power, it's probably not your cat that is the problem. :cool:

If engine temp continues to rise when the car is on the road (like on the freeway) is a good indicator that it is starting to clog up.

AFJuvat

I always thought the test was

Take it off look into it. If you see anything at all (honeycomb stucture ect.) then it was bad. All you have to do to fix it though is take a metal rod to it, cleans it right out. ;) ;) ;)


Of course I say this in jest

I think you can just take the car to a muffler shop and they can look at the temperature before the cat then after the cat and tell if it is bad.

Before and after temp is the factory method in the repair manuals.
---Wil Ferch

Before and after temperature
Before and after 4/5 gas reading
Cat temperature running, should be hotter than exhaust pipe

Exhaust pressure only tests for flow, they can fail and not clog. BTDTGTTS

You can always tell when it's time for a new cat...it's when the old one is laying on it's back with it's paws straight up in the air and it's as stiff as a 2 by 4!! THEN, it's time for a new cat!!

Funny.

Thanks for the responses, i do not think i need a new cat at the moment, just trying to find a good excuse to buy a new exhaust system. Honey, the cat is dead, if i am going to swap it out might as well get SSIs and a free flow muffler while i have the car up :)

Save the $ on the new exhaust and just put in a cat by-pass pipe. You can do it for well under $300 and get about the same HP increase.