I have an 07 mustang gt and i just changed the stock exhaust to an o/r x pipe from bassani and frpp stingers axle back. My mpg has gone down significantly. I dont have a tuner to turn off the rear O2 sensors so my check engine light has come on. Could this cause my car to push extra fuel into the engine from the readings of the sensors or is it just me driving it harder since it sounds so good now. It seems that im driving it the same. Also my exhaust has a noticeable stronger smell now? This is from the cats being removed and the exhaust lubrication burning off from the install right? Any help would be greatly appreciated.