On my 99 F250 SD 7.4 PS, Auto trans. on the passenger side, under the starter selenoid, mounted on the fender well, there is some kind of a pump with what looks to be 2 vacuum hoses, one is piped to an oval shaped box next to the battery. A small black thing that is making a LOT of racket and vibration. It's driving me crazy. I need to relace it, but I don't know what it is. Is it crirical?
Thanks