I have a '93 Bonneville SE and I replaced the plugs and wires and the car still runs rough and the car seems to BOG down between 45MPH and 50MPH. It'* like it won't stay in 4th gear! My gas mileage is also CRAPPY. I thought it may be a clogged Catalytic Converter so I banged on the Cat when it was cold- NO rattle! I checked for trouble codes and there are NO trouble codes- only Code 12 (System Pass)! I also checked the transmission fluid. It'* O.K. Doesn't smell burned and is still RED. Any ideas?

How old is the O2 sensor?

Ordered an O2 sensor online. Will follow up in a few days. Thanks!

O2 sensor was fine. I decided that I would replace the Cat after all! The way the car runs rough and the poor gas mileage all POINT to a clogged Cat! I bought a Universal but I don't see a notch or an arrow etched into the metal to show me which side is Inlet/Outlet. Both sides are 2.5"

I would guess there is no backwards. I would check for a cracked exhaust manifold. Try cleaning your MAF.

Thanks Nighthwk12! I will make sure to check those things. I called the manufacturer of my universal cat. and he said that it does NOT matter which way you put the cat on. You guessed RIGHT on! Thanks again!

Thanks DANTHURS and NIGHTHWK12 for your help!

No problem at all, any time.