Do the 500 EFI have the cool fuel system? I am having some issues, and it seems to be acting exactly like the issues on my 454 Mag MPI's.
Seems like vapor lock issue. I had the cool fuel system removed from my BAJA and never had the issue again.

We have replaced coil and a number of other things all to no avail.

Thanks

500 efi does have cool fuel at least the ones I built, fuel pump and cooler / housing are in front under the crank balancer

Like speedy says, down
low in front…. the 575’s in your cig had them on the same location

What issues?? When engines are hot and then docked for 30 ish mins, they fire and then sputter and stall??? Usually happens more on the port engine??

Yes, when hot after sitting for a period of time- fires up then dies immediately. Starboard side.

I had the same situation which was resolved by installing a new mechanical fuel pump on the seawater pump. The engine needs a good mechanical fuel pump to overcome a vapor lock situation.

What REVELOCITY said or a electric feed pump.

I just leave the hatch open and never have an issue because I have been to lazy to add the feed pump.
Mercury does have an electric pump kit I think for the fix. Been a while since I looked it up.

I had an issue with my 525's once this year and I have an electric fuel pump them since I have the whipple SC's on them. Of course, it was 106 heat index that day and now I leave the hatch cracked just a touch. Mine was the port motor.

When it happens again, press in the shrader valve and see if air or fuel comes out. Have a some paper towels handy. If air, then its prob vapor lock. I only have the OEM cool fuel pumps and no mechanical pumps on my 502mpi's, so not sure if the mechanical pump could be a contributing factor.

Early on, I used run some E10 fuel in my 502mpi's if I knew I was going to use it quickly. The E10 fuel made it vapor lock a LOT more, especially above 90* and humid. Hasn't happened to me for years now running good fuel and I crack the hatch 6 inches after docking on extreme hot days.

Thanks for the advice guys. Looks like a winter project.