Looking for a common thread... efi doesn't like to work with low voltage and a starter won't work with low voltage....

x 2.

Two local boats the other year thought they locked up one of their motors, both got lucky that it was one of the drives. Never would have believed it, since never heard of it/seen it, then Bam, two boats...same summer.

x 2.

Have fixed a ton of boats carb'd/efi with loose or bad cables/cable connections to starter post or at battery or engine ground.

OK first off the boat will start once cool with the drive on....however I will run it in the driveway today with the drive off. The drive spins freely off the boat and sounds good. When your buddies boat drives locked up were they stiff off the boat? I doubt this is the problem but who knows maybe its getting hot and seizing but when it cools down releases somehow.

Next the starter and/or alternator seem plausible. Thinking if the alternator went out it would run on the battery until the battery drained enough to kill voltage to the ECM causing a problem like mine and then not start back. Once it sat there for a couple hours the battery voltage might have been enough to start run for a couple minutes and die again. So today I will disconnect the battery while the boat is running in the driveway to see if the alternator is powering everything or not. The old school test should work for a EFI engine or does the main engine ground connect to the battery? The only odd thing about this theory is the starter should have went click click click instead of trying to turn over the engine. Maybe the ECM is more power hungry than i thought and it was enough to try and turn the engine but not run it.

The starter cables I have taken every connection off weeks ago and cleaned every cable connector and the start post. If the starter goes bad is there any reason why it could kill the engine while running? less a bad cable towards the engine side of course. I will look at these thoroughly today.

Doing this and you can blow the regulator in the ALT

Is the starter staying engaged

Im ashamed to say I dont know where the volt meter normally reads but when I had the problem it said 12 vdc on the money and when I tried to start it it goes down to 0. Dont know if its normal or the gauge is bad but Ill check it. i would think 14 vdc would be normal while running but mine was at 12. Other than taking the alternator off and having it tested what other test can I do?

I dont think so but honestly I dont know the hood was closed. It hasnt every stayed engaged before.

Motors would not turn over with drives on. With drives off they turned over and started up. Drivers where locked up. Shrapnel does things like this. Lol.