So I just scanned over this, so you have crank ( engine spins ) but no fire at the plugs ?

Does the tach read at cranking? (If it cranks)

Cranks….tach moves slightly….i couldnt imagine the rpms being over 100/200 on just the starter

you might still have a voltage / ground issue or whats the voltage at the starter and grounds wires on the bell housing , connections on the fuse on the starter all tight, have you pulled the cannon plug to see if there is any corrosion

The voltage at the starter is 12v on both sides of the fuse and i pulled the cannon plug and its clean as a whistle…i even spreaded a couple of the prongs to make sure its getting positive contact……performance marine (repair shop) has the diagnostic scanner for this setup plus they have experience with these 8.1’s so im gonna call them tommarow and see if i can get in there on tuesday…..i had reached out to a mobile boat tech and he put me in contact with this place after i picked his brain and told him all the things i was able to check with my automotive abilites…..nothing really left for me to check without a proper scan tool……im not gonna blindly throw parts at this thing with my fingers crossed……..i need verifacation on what the problem is, its not like your old school small block chevy in a old pickup where you only need air,fuel,and spark

Also I read that if the 5 volt circuit somehow got grounded it wont start, I think your cranking rpms should be closer to 400 - 500 revs

5volt circut would be feeding the crank and cam sensor……any other sensor that is 5v, what about the map sensor…that one is easy to get to, the crank and cam not so much….