You run rich, the excess fuel burns up in the ford catalytic converter
. Run too much extra gas, and you'll start torching up the innards of the catalytic. Bad news if you live in an area with stringent emissions testing. If I recall, an OEM cat will run you quite a bit, I was quoted 800 for an oem one by my local dealer.
1. Fix the excess fuel problem. This will keep the life of the second catalytic up, and will also keep your fuel costs down in the long term.
2. you can get an oem catalytic that's 50 state legal from magnaflow in varying diameters for a fraction of the cost of an oem. Just need to get it welded up.