i dont know what year your car is but some later models go crazy when you set the rear o2 codes to no report and keep commanding the catalyst efficency test resulting in a massive fuel dump just get a spoof and be done with it
I think its 2001+ cars that have this issue.
Regal GS Intake Headers 3.5mps pulley 1.9 rockers ZZP throttle body and Blower Wideband DHP