I have a UEL Header and two factory CATs with the fowler installed on the second CAT. The car is ( OBD 1). It had a resonator which I removed and then have the Magnaflow 6" factory polished tip muffler which im super happy with. Now everything has been fine with no Check Engine Light until today. But last inspection I was told by my mechanic that he had to test the emissions twice and it barely passed. I think it's time for two new CATs.