502 MPI Fuel Delivery Problems!!!
 

I have a 98 502MPI with cool fuel. Fuel pressure was fluttering between 18 and 22psi. Than drops to almost 10psi. (Noticed that reference line on regulator side was bulged) Removed and replaced pump and still doing the same thing. I guess my question is what else would restrict fuel pressure. Regulator maybe, and if so which one is the dummy. Any help here would be greatly appreciated. Thanks Guys

have a 1999 454 Mag, doing the same thing, I changed the fuel pump, regulator and filter, got pressure for a second, but had a fuel leak, got thata fixed and then 10-15 psi....motor just stumbles and dies. pulled fuel filter back off, and it was only 1/2 full. so i empeid it and tried it agian, and then the filter was empty. was told to fill filter up and try again. going to do that tongiht. Very expensive toy, not to be able to use it.

Im having the same problem and replaced my fuel pump. Any ideas???

I will be following this thread closely as i have a 2000 454 MAG and last summer i had about 5 incidents where after a run to our favorite sot and then sitting for a while i would have a no start pro lem, it would just crank and almost catch but not quite light up.
My buddies think somethings getting hot and maybe vapor locking or such because usually it will fire up after i raise the hatch and continue to try to start it after a few minutes(usually less than 10 minutes)
since u guys replaced fuel pumps and no joy i wonder if it could be a electrical problem.
Sorry for the hijack, i hope u guys get running right and quick.

Doug

check your fuel pump relay and wire . Changed mine out
no problems!

You can also check the fuel tank vent and or the pickup tube in the tank. In my area mud dobbers like to build nests in vent tubes & especially outboard discharge pee holes.

The MPI engines (454 and 502) are notorious for vapor locking. The only sure fire way to stop it from happening is to return the fuel to the tank, instead of the fuel filter head. This is a definite fix.
Eddie

You are for sure vapor locking. It is a known problem with the cool fuel system. Merc has a booster pump kit that will eliminate the problem.

I had the same thing happen with my 2000 502mpi's a lot on a hot weekend when I had ethanol in the boat. I never run any ethanol anymore and the problem is 95% gone. Once in a great while, it will still do it, but hardly ever. The booster pump kit is the cure, but I didn't want to spend $350 per engine for something that only happens once in a while.

The regulator you need to change is the one on the fuel cooler and if you are only getting that low pressure without the engine running (cycle the key a few times to see if it will go higher) then you don't have a restriction, it is a bad regulator.

so this kit, where is it and what does it do exactly? anyone make a home made copy?