You have to understand what MAP sensor does to understand the issue , without load on the boat , it runs fine , but once you fill the ballast and put a load on the engine it's spits and sputters ..... Next time take some carb cleaner and spray around the intake manifold and around the sensor , does it change the state of engine ? Rev or bog ? ..... Absolute manifold pressure , you getting any backfire ? If so is it coming through the intake ? Most times a air leak would be the culprit , but it also could be injectors or if the intake is plastic molded . Could be a crack .
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