Wow. If you dont have any 02 sensors then your engine light will be on and you wont be able to tell if your car is running lean or rich. Why would you want to take them out in the first place? The front 02 sensors tell you if your car is running lean or rich, the rear ones deal with the cats. Now if you have an o/r mid pipe (no cats) then you get mils which turn the rear 02's off.