If you have a clogged cat...I guess what I'm looking for is symptoms for a clogged cat. What's the worst things that can happen?

 

The motor will run like it has something blocking the exhaust: namely, it won't rev, especially under load; and eventually it will try to blow out something, usually the check valves in the AIR system. Guess how I know that. When that happens, whatever the exhaust blows on, will melt; wiring, hoses, coolant recovery bottle, air cleaner parts, etc. etc.

Let's work it from the opposite direction: what does your car do?

 

Feels like you are pulling a semi behind you. How do I know? My cat plugged and this went in its place.

 

The double post