90 7.3 fuel problem

[mikey11211]

hi all,,just joined..i have a 1990 f350..7.3 non turbo..its losing its prime after sitting for about an hour. ive replaced the manual fuel pump and it started fine for about 3 weeks..now i have to hit it with ether every morning to get it started. i just installed an electric fuel pump between the tank and the manual pump...no good. im guessing the problem is between the manual pump to the fuel filter? maybe a defective manual pump? when i bleed it i get alot or air out before fuel starts coming out...on the other hand when i cut the metal fuleline before the manual pump,, to instal the electric pump no fuel came out. now what ? any help would be greatly appreciated ..thanks
mike in nj

 

[flareside_thunder]

I'd remove the manual pump completely and run just the electric. However, you need to move the electric closer to the engine itself. Also, the electric pump shouldn't exceed 6 psi in pressure. The higher the pressure, the more advanced your injector pump timing can become. Do you have any fuel leaks anywhere? This sounds like it may be an intrusion issue. Alot of the normal places are fuel return lines, fuel heater mounted in the fuel filter head, the water drain on the bottom of the fuel filter.

 

[Fellro]

The leak doesn't have to be externally visible. Typically, it will fire fine, then die if it is an air intrusion issue that allows the fuel to drain back to the tank. The o-rings and fuel return lines at the injectors are the usual suspects.

 

[mikey11211]

thanks..like i said when i cut the steel fuel line along the frame to install the electric pump (was told to do that so the bowl stays full) there wasent a drop of fuel that came outa the line. shouldnt fuel have came spilling out being that its like 4 feet from the tank? and i got a good 2 months outa the truck after installing the new manual pump. should i start by replacing it again?? mayb a faulty pump? or should i start replacing o-rings?

 

[Fellro]

That is indicative of the drain back problem for certain. The o-rings allow air into the system, and it in essence siphons fuel back out of the filter a bit. Think of a straw in you dink. If you have ever put your finger over the top of a straw and held the liquid up then released, it is about the same thing. The o-rings leaking air is like letting go of the top of the straw.

 

[mikey11211]

ok...checked fittings..o rings...lines..got fedup with it so took it to a shop after a week of agrivation..they said the battries were week and that was the prob..wasnt cranking fast enough to get the fuel up. they put new battries in and said it was fixed.,. sound like a possibility or did i get a lazy machanic that didnt wana be bothered? im gona try to start it tonight wen is good n cold...kinda leary on this fix they did

 

[flareside_thunder]

Sounds pretty damn lazy to me. You ain't in Florida by chance?

 

[Fellro]

Batteries don't cause a system to lose it's prime, only make it easier to crank it out of it...