I put defoulers on my f150 and it stopped it from setting cat codes 99% of the time. Every few months under the right conditions it will still set the code. The reason mine is doing it is the previous owner dropped a 5.4 in it when it came with a 4.6. He didnt change anything else just the engine. Its not very happy about it. I dont drive the truck that much so I put up with it

Moving the o2 sensors out of the stream with the defoulers really helped.