U know what, that pretty much happened to my SHO. The ford warranty decided to replace all the injectors while they replaced the faulty one. Two days later I had a code for a cat that would come and go every other day. $650 for a cat is a lot cheaper than what the dealership quoted me for that part. They wanted $980 each. PPE catted downpipes(pair) was 700 or 800, so I went with them. I hope you won't have to deal with a cat. But if you do, I recommend PPE. I would get no codes on the factory tune with those.