My cats are known failing (sound like rattle cans) and I recently had 2 instances of cylinder 6 misfire. Cleared the codes and been ok since.

What cats are folks going with these days - just welding in Flowmaster cats only, or perhaps the entire set of pipes and cats from the likes of Magnaflow?

thanks!

 

Bad cats won't cause misfires, but misfires will cause bad cats. I've just welded in the flowmaster spun style. I did headers and larger diameter pipe at the same time and I'd really recommend it if you've got the ability. I did 2.5" pipe in the y-pipe and 3" single out the back and all mandrel bends and it made a noticeable difference in the 2 miles before my crank position sensor went out. I'm working on that today.

If you just cut out the factory cat and weld in the universal style then the pipe won't line up just right and you'll decrease flow, but if you're not worried about that then that will work fine.

 

Bad O2 sensors will cause misfire.
Bad speed sensor.
Bad wires.
Bad plugs.
Sticking valves.
Failing fuel pump.
Bad gas.

For codes
http://enginecodemaster.com