Looking to get all 4 of the stock cats cut out of my truck and get 2 magnaflow high flow cats installed to replace them. Will the CEL come on with that setup. And can I expect any mpg increase from this setup

 

Maggie's are known to burn out. That is no good. I would either cut the back two out or cut them all. You can do the 02 gotts. That will get rid of any cel

 

And you might get .5 ish. That's a big maybe though.

 

You won't gain anything from them, I have a set but I also didn't buy them for mileage. I bought them so I could have loud exhaust without getting tickets. My truck progressively has gotten far louder then when they were first installed so maybe they do burn out like previously said, I have never checked nor do I care enough to check. They're there and as long as they're there I can't get a ticket.