with the engine off and cold. tap on the muffler with a rubber mallet and listen for a rattle. kinda sounds like change shaking in ur pocket. if you hear it then its possible that its full of crap. then let the car run for 15 to 20 mins. turn it off and look at the cat. if the cat is red then yeah its bad. if you had a bad coil then the gas wasnt getting burned off and got dumped into the cat. it will clog the cat depending on how long it was bad. the smell of gas should come out the tail pipe till the cat gets hot enough. after that the smell should be almost gone. if the smell is still strong after 20 to 30 mins of running then the cat is clogged up.