ok i have another problem, so we got the my motor running, its a 94' 502 mpi mercruiser with a whipple sidemount. I took out the mefi-1 computer and upgraded it to a mefi-4. Well im having some fuel pressure problems. I have 50 lbs of pressure at idle and when i rev the engine up, but when the supercharger gets into boost the fuel pressure drops to 0 lbs. So my fuel system is set up as follows. -10 from tank to fuel/water separator with 1/2"npt inlets and outlets. (no anti-siphon valves on tanks) from there -10 to aeromotive A1000, then a after filter. From there a -8 to the stock fuel rail that is machined for bigger injectors (56lbs). Out of the fuel rail a -6 to the fuel regulator. And then the return off the regulator to the inlet side of the fuel/water separator. So any ideas about a solution? thanks

nobody has any ideas

I wouldn't run the return to the filter with a pump that big. Merc can get away with it because the pump they use in much smaller. That pump is returning probably 98% of the fuel at idle. It will not only heat up the fuel, but it will also aerate it. It really should be returned to the tank. If you do not have an extra bung in the tank, I have a few ways to do it.

Have you looked at the pickup in the tank. I understand you have big lines, but most of the boats I see have very small plastic pickups. You will more than likely need to up the size of the pickup.
Here are some pics of a stock plastic pickup from a Donzi 26 ZX along with some pics of the ones I make. The hole in the stock pickup where the tube meets the aluminum 90* was only about 3/16" Definitely not enough to support an SC engine. Hope this helps, Eddie.

Make sure you are getting high 13's to 14 volts at the pump. If you are then it sounds like your pump needs a rebuild. Also why are you running such high psi @ idle?

you will solve this problem by running an accumulator. the issue is that , while the pump can probably deliver the fuel you need at the appropriate pressure ( make sure of that) what it alsmost certainly can't do is suck from the tank that fast.

you need a high volume , low pressure pump as a lift pump from the tank to a 2 qt or more container . enters the top of the container and there is a return to the tank from there as well so it doesn't pressurise. THAT container gravity feeds the hi press
pump which drives the fuel rail and the return can go back to the accumulator tank or back to the main tank....your choice. i never liked the idea of sending it back to the seperator.

hi pressure, hi volume efi pumps tend to be vane type which pump like crazy by don't lift very well at all. a typical low pressure carter will lift like crazy but not make much pressure ... which you don't care about.

with this system, if your hi press pump is sufficiently sized, then you are home free. the lift pump should have a specification for flow rate of 200 % what your motor requires at wot

i would like to thank young performance for spending alot of time on the phone with me to help with my problem. I wish you where close so you could just fix it haha. Well anyways im going to try and fix it 2morrow so i will keep you guys updated

also i forgot to give you guys more info, im picking up from two tanks and then run that low on the transom, then it runs into a T and one line out from that to the pump (all -10) The pump is level with the top of the tank.