I have a 1999 502 MPI with a malfunctioning E.C.M.#3. Merucry Marine tells me that the E.C.M. i have is no longer available. Is there an aftermarket E.C.M. avalable or can i use a different Merc. E.C.M.

Might not have too hard of a time finding used one. Could also post "wanted" add on variouis cities with craig's list.

You are correct, the MEFI3 ECM is NLA for any application. Have been for a while. Mercruiser sells a MEFI4 replacement kit (part # 895104A01), which is the best fix, but a pricey one. Don't know why they would not have told you that.

Or you could try reflashing your existing ECM, or finding another one from a different application and reflashing it.

Dave