Boat ran great all day, no issues. On the way back in she surged a few times and then lost power and shutdown. Fuel gauge is not working well(when do they ever) so I thought we ran out of fuel. Got towed in fueled up put it back in the water yesterday, she was vapor locked got it going with a little starting fluid, ran great all day then on the way back in she died the same way. I’m thinking coil??? Or water in the fuel filter??? Help please.

Have you put a new fuel pump in it?

no I have not

Which 454 ?

Please don’t answer Chevy

It wouldn't have been vapor locked if it was a cold motor. A bad coil wouldn't have been affected by using starting fluid. No spark is no spark. I think your fuel pump is toast.
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Haha! Mercruiser Gen 4 Magnum H.O.

Pull the fuel filter and dump it in a clear glass. Wait a few minutes and see if if there is separation.