Bad cat?

[Erich Zeppelin]

My SES went off, checked the code, showed a bad cat. I replaced all 4 O2 sensors hoping that would fix it, but no. My question is, will my mileage drop with a bad cat? I went from 14 mpg to 12........

 

[IMINYOURCHAIR]

a clogged cat can restrict exhaust flow, making the engine work to pump out the gasses and reducing the mileage as a result. there are ways to check for a failed converter but I can't remember them all off the top of my head.

 

[FordandPolaris]

Does your exhaust smell like eggs? Often failed cats don't scrub out the sulfur like they are supposed to causing stinky exhaust. Also are you down on power?

 

[Erich Zeppelin]

No bad smell from the exhaust, but she seems a little sluggish, may be my imagination though.

 

[98EXPnSRQ]

There are a couple of youtube videos about testing cats. Basically, they used an IR heat gun to measure the temp before and after the cat, or you can use a pressure gauge, drill a small hole before and after the cat and measure the pressure differential.