Quoted from dsuperbee:Absolutely not true. I ran an off road x pipe on my mustang for years, and the error code would pop up in about 30 miles. Had to turn off the rear o2 sensors with a hand held tuner.
Doubling up spark plugs anti foulers are what the kids are doing and allows enough pollution through that computers thinks cats are there.
SCT got busted by the EPA back in 2018 and no longer able to have the programmers be able to turn off the rear O2’s. So there’s work arounds as mentioned above.