I havn't done anything to it yet, I'll do a comp test and check the plugs.. car only has 108,000 miles on it.. if its got low compression, I'll just run with it cause the car isn't worth it. I paid $500 for it with hopes it would last the winter.. it seems to have all the power it needs so I doubt it is the cat cause I know what happens to performance when they clog.. but it is a factory ford exhaust system, I can get it to operating temp and check the cat with my non contact pyrometer. ( 5-10* hotter on exit side of cat means cat is operating )...

It only cost's $29 per week to fill it up, so it's not that bad to drive, just if I can improve the MPG for less cost than 1 fill up, I would.