I'm w/ the tune posts and to add,whats the fuel pressure?

It also seems there is no tstat as it doesn’t get up to temp. Doing some other reading this could pose a problem as well 🤷‍♂️

You have a pic of frt of your engine so we can see what cooling system it has ?

I’ll get one. Has brand new sea water pumps and pulls from the bottom of the hull and out the exhaust.

How hot is it getting, ECU still could be adjusting fuel for cold engine?

It’s not moving the needle on the gauges. I don’t know if it’s a gauge issue, a temperature, sending unit issue, or it’s just not getting up to temperature. Lots of trouble shooting to do.

previous Owner claims there are thermostats in there

whole lot going on here but my first guess it that it had ProChargers on it that are now gone and if it was tuned that is what it was setup for. you have a vacuum hose with a screw in it, where is that going? it does not have a thermostat with that setup so it will struggle to make temp especially with all that fuel running thru it. not sure if that ecm is looking for water temp to go adjust it but odds are that alot was changed before you got it and they just made sure it would start so they could sell.

correct the boat did have a pro charger at one time. The vacuum line goes to the fuel pressure regulator, I think. I do not believe the pro charger was set up on these fuel injection units. I’ll have to dig through the photos. previous owner definitely wanted to sell. Previous owner “claims” it has stats. I’m OK with working out the kinks based on what I paid for it.