I bet it's missing that check valve then. You can just run a piece of diesel imersion rated line line from the sender return line to bott of tank and do the same thing

 

Sounds like text book air intrusion. There was a Ford issued technical service bulletin to remove the return line to the filter. In theory, it was to purge air. In reality, it allows all your fuel to drain back to the tank, and leaves you with a half empty fuel filter.

 

I'd leave it and put a 5psi poppet check valve or an fpr

 

oh, ok. 4-5 seconds of cranking before starting on a cold engine is not long at all.

 

so the people on oil burners know better than ford engineers? it is not to let air bleed out of the filter. it is to return a portion of the unused fuel back to the filter instead of sending it all back to the tank.
and there is no way it would ever allow air out of the filter head into the return lines if it was functioning properly, there is a one way check valve in there that prevents anything from flowing out of the filter, the valve only allows from the return lines into the filter. that is why the TSB to remove the line and plug the filter head was issued, because the valve failed/leaked allowing air into the filter and letting the fuel drain out of the filter back to the fuel tank.
mine has been disconnected for the past 26 years and close to 390,000 miles without any problems at all

 

easiest way to test is to remove the fuel filter before starting cold. if it is full, the fuel system is fine.

 

On my truck and the parts truck i bought, when i remove the fuel line from the filter fuel comes out with an electric pump. With the key off (no power to FSV) and fuel pump on i could hear air being returned to the tank on my parts truck which is how i located the air intrusion.

My filter head line ties into the fuel return lines and is definitely under pressure, the return caps are under almost none and i dont see how it could return to the filter unless the fuel return caps on top of the injectors were under a greater pressure than the filter. My understanding is these caps are under no pressure.

I think the ford engineers came up with that fix becuase if there is an air leak at any injector caps, or the duck bill has fallen off in the tank and youre below a half tank, then it can drain the filter and cause hard starting issues. If there are no leaks and that check valve on return line is intact or below fuel level there shoul be no reason the filter head would cause issues. It's cheaper and easier to plug a degassing setup than having mechanics drop a tank or replace injector caps.

so long as fuel doesnt slosh too low, there shouldnt be any issues with having it plugged but i still believe it does serve the purpose of bleeding air. its tied into the injector cap returns, which even if they were presurized to say 10psi to overcome incoming fuel fitler pressure, are tied directly to the fuel return which is open to the tank and would bleed of any pressure on the caps anyway so it could never over power the fuel filter incoming pressure

 

fuel return lines are under pressure.
the line out of the filter head is leaking out into the return lines because the valve in the head is bad. it should only allow fuel to go into the filter head, not into the return system. cap it off, and your truck will run better because you will then not be bleeding fuel pressure into the return line system, all the fuel will go to the injector pump.

 

I dont have the factory filter installed anymore but i am installing a swagelok 5psi poppet valve at my injection pump because i think a full time air bleed and consistent pump charge pressure are key to a long pump life. The valve will go where the barb fitting is then the to the fuel return line back to tank. I will pull the checks on both filter assemblies i have, even if failed, and take pictures of their orginal design direction. Do you have the orginial TSB that recommends this fix?

 

no i don't, it was issued around 1990 to help prevent air intrusion.
i went looking for it a few years ago, but all-data and the other recall/TSB site i used to use went from free lookup to paid subscription.

the system you have is pretty much all together different than the original setup.
with the facet duralift pump on my 88, i would not see air intrusion issues even if i had them, because by the time the glow plugs cycle, the pump fills and pressurizes the filter and injector pump at 9 PSi before i even engage the starter.

 

I wasn't questioning if it existed or anything just curious what it said and their reasoning. In my experience with chemical injection systems eveything in this setup to me is designed to be a degassing setup. I'd be willing to bet that the check valve in the filter is actually a poppet valve and is designed to opened at a preset pressure similar to what I've done with mine. It wears out and is no long a preloaded check valve and allows it to drain the system. I'll disassemble the one I removed tomorrow and verify with the one on parts truck. It should be obvious which way it was designed to flow when I take it apart

 

Yeah, I want to know that too.
I really don't see how the return system could /ever/ have enough pressure to allow fuel back into the filter side of things, unless the return line to the tank is blocked.
The supply side of the filter should be at ~5 psi, the return should be free-flowing back to tank.

 

Please do, I wonder if plugging it will cause damage

 

How does one plug the plastic injector cap with out looking like ***t

 

when i did mine i simply cut the line and stuck a bolt in the line with a hose clamp. the return circuit only has 1-2 psi pressure in it. then i put a brass pipe plug in the filter head.
i ran it with the bolt in the line for a few years, and eliminated the line with a single tap cap on the injector the next time i did a return line kit.