I have a 94 7.3 n/a. It has classic air intrusion symptoms (starts, idles, dies, crank 10 seconds and starts fine and runs fine). Here is the problem tho. I have recently had a new injector pump installed, all new injectors and new return line kit installed. I even switched out the cheap hose clamps for the more serious screw down clamps. The lift pump prolly doesn't have 5k miles on it. There is no fuel leaking and no wet hoses and frankly I am tired of trouble shooting this thing. I am wondering if I install a one way fuel valve right behind the lift pump or install an electric pump if that would solve this. Any suggestions would be appreciated.

 

air molecules are smaller than that of the diesel fuel. it is possible for air to leak in but it not leak fuel out. i cut several of those injector o rings when i installed my first return line kit and was kickin myself as fuel shot out of 2 of mine.... i changed those and it still had a hard time starting found out by lucky guess that my back drivers side was not sealed properly and got that one changed out no problems since

 

well naturally an electric fuel pump solves, not air intrusion problem but hard starts due to air intrusion,cus your no longer trying to pull fuel up and relying on suction.your pushing fuel into the line,and the e-pump could care less what happens to the fuel lines after it.nor does it matter one way or the other if all the fuel drained back into the tank,cause before the wts lite goes out,your going to be fully primed again anyway.
from then on,all you have to worry about is leaks.simply fix them as you see them.meanwhile though,you'll start the truck and it will remain running.no more screwing around with yesteryear's problem as far as air intrusion goes.
leaks however....well,got to love the idi.

the old fuel pump becomes removed whenever an e-pump is substituted for full time use,and is blocked off using a block off plate.
a relay can be used and activated via the FSS to directly connect the battery to the fuel pump (making sure NOT to pull current directly from the FSS!!!) with the turn of the key,or a toggle switch can be used.

there is only a few requirements.
that you make sure,not to push fuel into a mechanical pump (least not full time.)
that you get a pump rated for diesel fuel.
that you get a pump meeting the psi and flow rate of stock,or tone down a higher rated psi pump with a regulator.
run clean fuel.
don't run the tanks dry.
keep filters serviced.

 

Did You change the fuel supply olives when You changed the IP?

 

Not a good idea. Screw clamps do not clamp uniformly around a small diameter. And could possibly deform the hose, allowing air intrusion.

 

I would say you need to look at redoing the return lines. Electric pumps don't fix the leaks, they simply hide them and mask them. As mentioned, screw clamps this small don't work evenly, but a good quality hose and o-rings will make a big difference.

 

Thanks Fellas. It was starting right up before all of this work was done. It didn't matter if it was cold, hot, sat for a week, whatever; every time fired right up. I sure miss those days. Anyway, I am gonna try to rework the return kit and see if I can't get that straightened out. I had no idea about the screw down clamps. I will surely replace those. Just got my truck back from the exhaust shop yesterday. Dual three inch pipes are rather loud. I'll take pics and post them in my gallery. Plus, I did my own version of installing a K&N air cone. I would like to hear what you guys have to say about it. I'll start a new thread tomorrow.

 

Fonefiddy, what is a "fuel olive"?

 

Why would you not want to do this? I have heard of a lot of guys using electric pumps to assist mechanical pumps.

 

He is talking about the 5/16" Vibra-Loc - McMaster-Carr Item 50385K83 on the hardline from Filter head to IP.

There is also a 3/8" Vibra-Loc - McMaster-Carr Item 50385K84 on the hardline from Lift pump to Filter head.

Pushing fuel into a mechanical pump could very well fill your crankcase full of Fuel ...

-Enjoy
fh : )_~

 

OK, thanks, Festus

 

Are there just one each of these sizes? My dad's 91 7.3 is losing prime and hard to start after setting. He has replaced return hoses and return o-rings and no change. is there a check valve in the system? I've heard the lift pump acts as a check valve and that could cause this problem. Thanks

 

i believe there are 2 of each size, though i haven't been lucky enough to have to deal with mine yet

as for the multiple pumps, festus is right. however, you do have the option of having them in series with the e-pump only running by a pushbutton or whatever to prime the system. for mine, i have the e-pump between the tanks and the lift pump, with the e-pump wired such that it only runs whenever the glow plugs are lit or i hold a pushbutton.
all the symptoms of air intrusion are a thing of the past for my truck

 

Can anyone piint me in the direction of a good write up on installing a e-pump with a check valve between the filter and mechanical pump I'm tired of the air intrusion.......... I cannot find the leak, or I have found it and just cannot fix it

 

Been battling this problem last few years too.

Before starting , just try cranking and opening the Shrader valve ( bicycle tube type ) on the fuel filter. Confirm that fuel shoots out and not air. If you have air in the fuel filter, one common air leak is the fuel filter heater on the top. There are rubber O-ring gaskets inside that shrink. There is a good Youtube video on how to disassemble the filter and replace the O-rings for your engine. That solved my chronic air in the ff problem.

I think that if the ff is full, an electric pump is not going to help air in the return lines, but that's just my opinion.

I've had some luck , when the leak is small, with rubber seal swellers. 10% biodiesel, or transmission or power steering fluid with seal swellers additive ( one quart ) added to the fuel. Worth a try.

Our trucks are 25 years old! Most of my recent problems have been due to old rubber in fuel lines, pump diaphragms, O-rings, belts.