Originally Posted by iLUVBMWS
the reason you getting crappy mileage is your O2 sensors are not getting the correct reading form the cat delete, causing your ECU to put in more fuel, it's trying to get to the correct readings. probably why you're getting a SES code.
i have supersprint headers and i had the same thing, low gas mileage, engine ran erratic, plus SES code. to get rid of all that i put in O2 simulator, the engine really came alive, exhaust tone was louder, ran smoother and gas mileage back to normal. i never ran anything less than 92 oct though.
well i have the AA off road tune (stage 2) to it turned off my rear o2's so i had no need for a o2 sim's. but i havent had a SES light in over 200miles. Whats weird to me is when my rear o2's were plugged in i kept throwing ses light it was for the rear sensor how could this be if they are off well i unplugged them and no more ses light and crap millage still! lol
and all codes were for bank 1 sensor 2 voltage low input. and bank 1&2 both sensor 1's were stuck rich.