i removed my cat all together, and my cars running EXTREMLY rich (helps when i push it over 110mph) but i am getting crappy (around town) mileage, but anyways i removed my cat, and my O2 sensors are phucked, at first my check engine light came on for a while becasue of excessive NOX, and HC levels but i cleared them and the light doesnt come on for them anymore, it will come on once in a while if i dont let my car warm up at idle! for excessive cat threshold, but it turns it self off after 4 drive cycles! but other then that no real problems. also does anyone know where to purchase "O2 Eliminators" they send false signals to the ECM saying everythings ok! i've found them for almost every car but tiburons!

 

just hang the 2nd O2 sensors somewhere safe under the car and you'll never throw a CEL.. DSM people remove the O2 sensor all together and put resistor packs on it