29Fever01

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hey guys,

Does anybody know know what normal fuel rail pressure would be on a 500efi hp, with the coil wire removed, cranking the motor out of the water with no fire?

I'm getting 10-12 psi on my gauge. The reason I'm asking is my fuel system is not pumping enough gas to the engine at idle and throttle back trolling. I thought I had found the problem with the original mechanical fuel pump not pumping gas out the top when cranking the motor. Replaced that, and still had the same condition.

Thinking that I had more issies back towards the tank, I was told to look for an anti siphon valve and see what that looked like. Tonight I tore into that, and found that there is no screen, or anti siphon valve on the top side of the gas tank. At this point I have no other ideas.

triple 300s

Have you put a mechanical gauge on the schrader valve to see what it is doing? The electric senders are often not accurate.

29Fever01

Thats where those psi readings are coming from, thats a gauge that i put on the schratter valve.

mikesystem01

thinking your looking for a new fuel pump my man should be in the 40's if i remember correct i replaced one of mine last fall

29Fever01

quite possible, the electrical fuel pump you mean, but the thing that has my head spinning is that I replaced the mechanical fuel pump because i isolated it from the water/fuel sepreator by pulling the steel hose off of the seperator, cranked the engine and couldn't get one drop of gas out of the top side of the mech fuel pump. Thinking I had a smoking gun, I replaced it with a new one and still have the same symptom. Thinking I'm having a flow problem from the tank, I was adised there might be a screen or anti siphon valve on the top side of the tank so I tore into that to find there is neither one of those components in the tank, just a 90 degree aluminum elbow with a pipe going into the tank. At this point I am going to disconnect the fuel line from the bottom of the mechanical fuel pump to test it. Connect a clear tube to it, fill it with gas, and crank the motor to see if it spits gas out of the top, to prove the new pump is good. The only other thing i can think of is the small cam shaft that runs the sea water pump and mechanical fuel pump has an ovaluer coller on it that the duck bill operates on for the mechanical fuel pump. That possibly is worn out and not the original fuel pump. The other possibility is to look again at the fuel hose going from the tank to the fuel pump again for a small cut or something but I couldn't find any monday night.

29Fever01

has anyone ever heard of the collar on that cam shaft that runs the mechanical fuel pump wearing out? anyone have any other ideas?

jmoore1225

iTrader: (1)

it wouldnt be wore out unless the arm that runs the mechanical fuel pump was destroyed, dont ask how i know lol

Jpzaluski

Not to go off topic... but 500EFIs have mechanical pumps? Mine doesn't???

triple 300s

You should have one down off the impeller housing...no?

bob_t

First generation of 500EFI's don't have a mechanical pump, just electric. They (later) added it due to major complaints of vapor lock. There are a couple of "easy", somewhat reliable ways to tell which generation 500EFI you have ... later ones have a "ball" on the end of the oil dipstick instead of the "curl". Also, the headers were changed ... early headers have a straight piece of rubber hose connecting the header to the tailpipe, later gen has a "U" shaped jumper hose. With the earlier version and straight hose, you had to either slide the header forward or the tailpipe aft, to get the header off. Later version, you just disconnect the "U" jumper hose and pull the header straight away from the engine (nice improvement !!). Usually, but not always, the earlier gen don't have the mechanical fuel pump, and the later versions always have the mech fuel pump. I always look to see which jumper hose is on the header to tell if it is an early, or later, version of the 500EFI. .... just some more "performance boat trivia"