I don't know how your MAP is supplied with vac, but on the older Fiestas the pipe can get kinked/blocked and cause over-fuelling, so to save wrecking your new cat I'd be checking it as a matter of course. Depending on software level the engine warning light may not be illuminated, especially if it's within normal range albeit always rich.
If there's dirt/particles trapped under an injector nozzle it's possible it won't shut completely and drip fuel. You need it on the 4-gas to eliminate one at a time if you want to test, if the Co drops to spec when one cylinders injector is disconnected, you know it's in that area.