Well, I have an '82 Excaliber 38' with 2x 541 BB MEFI-1 engines in it. The port motor is fine. The starboard motor, which also runs my power steering pump, has an issue. It starts fine when cold or below 120deg. If I get it up to temp and shut it down, it won't start. I know the timing is dead on where it should be and every part of the fuel delivery system (2x pumps per motor) has been replaced to include all the lines.

Somehow, I think I'm getting vapor locked. I know it's not a false overheat code because I swapped the main computer out with a spare and that problem went away. Is it most likely vapor lock or could it be something completely different. As soon as it gets below 120deg it'll start right up and run great.

Swap the ECM and the problem goes away. This tells me its the ECM

Vapor lock takes time and heat. Your issue is instant as soon as motor is up to temp and shut down. Unless I missed something

It doesn't shut down on it's own. Once I shut it down for whatever reason, it won't restart until the temp drops to 120 or lower. Here's the thing, my gauge in the dash and the code reader both indicate at Idle I'm not getting past 150deg, so i know it's got plenty of water flow, gaskets are good, and it's not over heating.

Got it, but did the problem go away when the ECM (computer) was swapped?

who programmed the ecm's , what efi are you running

What problem went away ?

Please be more clear on things so we can follow and help easier.

So, did you check for spark and fuel psi when this no start happens ?

The false over heat code went away, but not the starting issue when engine is at running temp.

As for the ECM, they are the MEFI-1 and I don't know who programmed them. I did send the spares off to have the original starboard side fixed and both reprogrammed. Sent detailed specs of the engine builds along with them, too.

Thanks
When it won't start
Can you hear the fuel pump prime?
If yes, what is the fuel pressure reading (VST would be 37, but yours may be different)?

With key ON is there 12V at the coil during cranking?

Both pumps on this engine prime and are new. One gets it from the tank to the main pump and the main, well...sends it to the rail. I have two batteries per engine and all are new. Voltage is where it should be for the coil and that is also new. Fuel pressure is a constant 45psi. I have also checked for spark and am getting that, too. The TPS is also set correctly and reading the correct voltage, too.

Only thing I can think of is there's a problem getting fuel into the cylinders after the engines are warmed up and I shut it down for whatever reason.

SB, the false over heat code went away when I changed the ECM, but the no start problem still persists.

what EFI are you running asking again