Should I install a fuel check valve between electric pump and filter?

[QuercusRubra]

Just got a '94 f350 7.3L turbo IDI.

Before I bought it, the mechanical lift pump was abandoned and an electric pump added back near the tank. I'm having an air intrusion problem: turn the key and it starts for a second or two easily, but then dies and takes a lot of cranking to get going again with lots of stumbling and white smoke. Once running, it runs well. If I leave the key on so the electric fuel pump runs and push the Schrader valve on the filter head, I get a whole bunch of air before fuel comes out, so obviously its draining back toward the tank, right? I just replaced the supply fitting to the filter head and the fittings from the filter head to injector pump because they were suspect. Obviously I have a couple other places to check on the filter head, along with return lines and injectors.

My question is, did the mechanical fuel pump include a check valve to prevent fuel from draining back to the tank? Should I install a check-valve between my electric pump and the filter? I can't think of what that would hurt, but I thought I'd put the question out there and see what people know. OR is that not my problem and I should focus on chasing down the leak, wherever it is?

Thanks in advance!

 

[Ruger_556]

I never had a problem without a check valve running just an electric pump... I'd suspect return lines.

 

[redneckaggie]

dont really see what it could hurt but I have been without one for going on 6 years with electric pump and no problems

 

[icanfixall]

What elecric lift pump do you have on the truck. Many is not all electric pumps have an internal check valve. I know the Carrier lift pump does. It wont hurt to add a check valve but thats just a ban aid to your problem. you have a leak somewhere thats allowing the fuel to drain out of the system. how old or how many miles are on the injection pump, injectors and return lines.

 

[QuercusRubra]

Yes, I was kinda thinking that some if not all fuel pumps may have a check valve in them. Guess I should investigate what pump I have. Previous owner wasn't the type to go all out on fixing things, so I bet it's a cheaper one.

Truck has 197k on it, and I don't have any information that the injection pump was changed. Is that a likely culprit?

 

[icanfixall]

Well injection pumps have a life expectancy of around 125,000 miles give or take. So your well past that. Can you see any wetness under the injection pump. What about on the drivers side of the pump where the advance plunger is. thats a known seal for leaking on high mileage pumps. If the valley pan is wet then you have a fuel leak and need to find where it is.

 

[FarmerFrank]

If its one of those little green Mr.Gasket ones dont count on it for long. Only a select few have ever had luck running them for very long and they WILL NOT pull fuel very well. A 95gph Mr.Gasket, Holley Red, or Carrier pump is what you want. those will all pull fuel too in the event you accidently run out or some how loose prime to the tanks

 

[QuercusRubra]

Ok, I think I narrowed down my air/fuel leak a bit... Last night, after I got the truck running and warmed up, I crimped off the return line to the filter head, and left it. This morning, I turn on the electric fuel pump and hit the schrader valve and the fuel is right there instead of 5 seconds of air first.

Turn the key and it starts up pretty easily. Still rough and stumbly when first started, though. Repeated this evening, too, with same result, so I think it's safe to say the fuel's draining back because air's coming up through that return line.

So here's my question: If it's still starting rough and stumbly, with a cloud of white-ish smoke, that sounds like it's still passing some air in the fuel line? What's the relationship between the return lines and the fuel feed? Every body's talking about air leaks in the return lines... is there some way that gets pulled into the feed circuit or the injectors besides passing back through the filter header? It seems like the return lines are a separate equation...am I wrong?

I guess I could still be getting some air in through the return line that goes to the injection pump if that check-valve is bad, too?

Rough start and smoke could be a few bad glow plugs?

Could this be a problem with injectors themselves? uneven pop-off? leaking nozzles?

I don't see any fuel leaking anywhere, except where I spilled a bit out of the schrader valve.