200 HPDI power problems - 2001

[Britfish]

Dropped it in the water today and have a power issue. Did all the right winter things, changed the seperator filter, new plugs, drained the VST.
I'm reading it could be an o2 issue - anyone have any experience ?
Do I need to take it into a Yama guy ?
thanks for help

[boats.net]

Start with compression test, have fuel pressure tested.

[rodbolt17]

O2 sensor feed back is not used above 1500 RPM or so on that engine.

[Britfish]

Thanks for the advice, not to jump the gun, but whats the next step if I have a compression issue

[99yam40]

bad compression = cylinder/piston /ring problem most likely