how do you check to see if a catalytic converter is bad

I seem to have some power loss

Bang on the bottom of it with a rubber mallet or something. Mine sounded like it was full of rocks. Or take it to a muffler shop and have them do a flow test.

Dan

just wondering what exactly is a flow test, my cat is rattling like there is no tomorrow i havent got any good licks in with the mallet yet

Muffler shops usually do the 'quickie test':

Burn a quarter inch hole a couple inches in front of the cat.
If the sound/tone/performance of the engine remains about the same, then the cat is NOT plugged.
Then, they weld it back shut.

Midas has done this for me several times at no cost.

You could do the same with a drill, then seal it again with a large galvanized (NOT stainless unless your tube is stainless) steel self-tapping/self-threading sheet metal screw. Make the hole in the side, not the bottom (so moisture that condenses in the tube bottom doesn't promote rust).

Some cats are honeycomb, and the rattle sound is a signal that the honeycomb has broken (doesn't happen often).
Other cats are pellets, so the rattle sound means nothing.

Bottom line: Does it flow or not.

Good luck.
-Rick

This is an easy one.

If the cat is restricting enough to cause a performance loss then you can test it very easily without cutting into anything.

When the motor is warm & idling, take your hand & carefully feel the exhaust behind the cat. Now feel the exhaust pipe ahead of the cat, if the pipe is hotter ahead of the cat then it's plugging or plugged. If the cat is flowing fine the exhaust pipe will be roughly the same temp ahead & behind the cat.

A "CAT" is either good or bad, no in between. Trust me, I have designed a few at work. 95% of the time it will melt together into a glob. It is a honey comb looking substrate basically made out of different precious metals.