502 MPI Starting issues
 

Got a buddy with a 28 Sunsation. It has a mid to late 90's 502 MPI that has been bored to a 509 @ 550 HP. The engine runs great except he is having starting issues. The VST tank has been removed and he has 2 electric fuel pumps. Has a return line to the gas tank. After long runs he can shut it off and it will start right back up. If he shuts it off and waits 15 minutes it won't start. Just cranks and cranks. We checked the spark while it was in that condition and it's good. Has plenty of fuel pressure. If he waits another 15 to 20 minutes it will start right up. He just put on a new distributor cap, ignition module and Map sensor. Still has the same problem.
What should we be looking at next?
Thanks,
Steve

i would hazard a guess that the rail pressure is draining to zero when you shut down... leaking injector or regulator or something ... such that the motor is too warm to go to " cold start" enrich and doesn't have the starting rail pressure to get it to fire hot. i assume that his sytem is normally wired such that the pumps start with the key on and then cycle off after a few seconds ... assuming thats true you can generally work around the issue by running thru that cycle a few times before cranking to build pressure in the rail and cycle the air out.. but the fuel press should stay up for about 30 or 40 mins at least after you shut the motor off and if it doesn't you have a leaky injector or regulator... WHICH can often be fixed by cleaning them..

Yes it is normally wired and the pumps start with the key. We believe the pressure in the rails is up. There is a little port on the front of the engine just below the plenum. I believe it is for checking pressure. When you push in on it fuel sprays out under pressure. That is why we think have fuel rail pressure.

well... you are correct about that ... but how much ? if it bleeds down to 5 or 10, then that isn't goint to get it done yet will spray like hell. can you whack a gage on it and read it and watch it ?

I will have to get a guage to check it. What pressure should it be?

in a perfect world, system press. 37 and above but if it bled to 30 i could live w/ that. what you don't want to see is it crash as soon as you shut down

Mine used to do that, vapor lock. Check fuel separator when happens, mine was half empty during vapor lock and sitting for a while and rolling motor over eventually cranked in 20 minutes or so.

My buddy is trying to find a pressure guage, but is finding it hard to find . None of the auto parts stores have one. I think he will get it checked at a local marine repair shop next week.

there is a million blogs on here about this and sounds like Vapor lock,, Mercruiser has a service bulliten on this. We Formula guys suffer from this because they insulate the engine area so well..., Go to the Formula section on here,, and someone is having the same issue and that bulliten is in that string of messages.
Can bet you thats the problem.... Best thing is Mercruiser tells ya whats arong and OOHH WELL. tuff titty's.. but there are fixes...just search on here.. I bet I have read 100's of articles in this on this site.. Good luck