Mercury - Fuel Pump MerCruiser Sterndrives 42725A3. Overview. If you've spent any time working on the old 2.5L, 3.0L, or 3.7L MerCruiser sterndrives, you know the mechanical fuel pump is one of those parts that slowly fades rather than suddenly fails. The engine starts getting picky-harder to start, a stumble when you crack the throttle, or it just runs out of breath when you're trying to get on plane. This pump is the proper replacement for the versions with the filter bowl pointing down. It bo