Walt wrote:
Boat Tech wrote:
With the 6.2 it could be a number of things, But my first guess would be bad spark plugs.
Definitely do the compression check.
Also recheck the fuel pressure, But this time look to see if the pressure is bouncing around a lot, If it is then you may have an internal problem within the engine.
Good luck with it.

Before I swapped press regulators, I was running 35-38 psi. Merc said that was too low (spec- 41). After swapping the HP fuel pump and regulators got it to 50 psi idle, up to 55 at WOT (not wavering, or jumping)
In the spring I plan on checking the plugs/wires first, and doing compression check as I go. My intuition says intake gasket. My wallet is expecting it to be a head gasket or fried inlet valve.
50 to 55 psi is to high, Sometimes it's caused by a restriction in the fuel return line system, But keep in mind it could be a bad fuel pressure gauge as well.
Unfortunately with your intuitions/wallet ideas, That is exactly why I mentioned it could be a number of things from your descriptions above.
I hope you can get it runnin good once again, Good luck with it.
