I have a 1999 3.8 liter camaro that had 87000 miles on it and i blew the engine so i put a identical engine in it with 22000 miles on it. It ran really good and strong for about 3000 miles then one day i was driving it and it started having a loss in power.I pulled off along the road and noticed the cat. converter was glowing orange. It took all it had to make it home.I replaced the cat. and i took it out after wards and still ran like ****! It only will go up to 4500rpms and has hesitation when you give it gas. I checked the fuel filter and it was clean.The car will idle fine but runs awful! My friend pluged a code reader to it and it said multiple misfiring cylinders.I cant take it to a garge due to money purposes. I really need to know with the problem is.

 

change the plugs and wires

 

A cat that isn't plugged but glows red means your air/fuel mix is on the rich side. Your multiple misfire issue means it could be an ignition problem causing one or more spark plugs to not fire, or fire inconsistently. Or, you could have bad/leaky injector(s). Or, your fuel pressure regulator could be bad, raising the fuel pressure. Any one of those can make raw fuel "pour" out the exhaust, making the cat glow.
By the way, when you replaced the engine, was the WHOLE engine from top to bottom replaced? Or did you re-use your (possibly bad) old intake setup and ignition components?

 

You really need to look at the fuel trim data to see what it is doing a code reader is just that a code reader. Do a fuel injector drop test to check injectors and the fuel press. regulator. It does sound like it is running really rich.

 

Stupid question - when your cat grenaded, did it come out whole? I wound up having that same problem in another car (Saturn) where pieces of the cat basically plugged up the exhaust. Car had no power, and ran like crap when given gas. Would idle ok, but was REALLY hot.

 

His cat didn't grenade, it's just glowing red. Even though it might not be good for the life of the cat, it's glowing because it's doing it's job, given the circumstances. He has a rich fuel issue, and the cat is burning it up.