Possible air intrusion when parked uphill?

[TNBrett]

Three questions if you please:

1. So if I understand correctly, the lift pump normally supplies more fuel than the injection pump requires and that excess fuel simply flows back to the tank through a return line. One would think an alternative to this constant circulation of the excess/unconsumed fuel back to the tank would have been to incorporate a pressure-regulated bypass in the lift pump itself, such that only the quantity of fuel demanded by the injection pump would flow from the lift pump to the injection pump. Could you comment on this?

2. Why are there return lines on the injectors at all? Does the injection pump not meter the quantity of fuel delivered to the injector? Does it rely only on pressure regulation, always delivering more fuel than will actually be required at each power stroke? If so, then is unconsumed fuel continually flowing out of each injector requiring capture and return to the tank as with the lift pump (#1) situation above? Again, please comment.

3. If my understanding is reasonably accurate, I've seen posts offering modifications to eliminate the return line(s), stating something to the effect that doing the mod "solves the air intrusion problem completely." How could eliminating the return lines possibly work?

Thank you in advance.

I’ll take a crack at these. Cubey answered some of it already, but anyway here’s my take on it.
1). Another thing to remember about the IP is that it is cooled by the fuel flowing through it. The fuel returning to the tank is taking heat with it.
2). The fuel injectors have a valve inside that opens once the pressure reaches a set level. This is referred to as the pop pressure. As the IP sends fuel to each injector the pressure ramps up and then down. As the pressure is building, it’s not a problem for the injector to be closed. The incoming fuel is just building up pressure in the injector. Once the fuel reaches the pop pressure, the injector opens up and sprays fuel. The problem is once the pressure from the IP starts to drop off, the injector closes. There’s no longer enough pressure to hold the injector open, but there’s still fuel coming in that has to go somewhere. So it’s allowed to bleed off into the return lines.
3). I’m not aware of anyone selling products to eliminate the fuel return system. I know some of them claim to to eliminate some of the problems with the injector return caps, like machines aluminum return rails, or machined brass injector caps, but functional they work the same.

 

[franklin2]

I don't claim to know all the ins and outs of this fuel injection system. I have been told the injectors have returns because they are designed to have a certain amount of leakage for lubrication and cooling. But someone else corrected me and said the return flow from the injector is from clearance around the internal parts of the injectors, and that a brand new perfect injector will have almost no flow through it's return.

Whatever the case may be, I know just enough to keep the system working. Something that I always fall back on when working on these vehicles, if Ford could have saved a dollar on each truck, and made thousands of trucks, they would have saved thousands of dollars. The return system is on there for a reason, I am assuming if they could have eliminated it they would have. I said Ford, but really this design came from International. Ford just dropped it into the chassis.

And from what I understand, the stock fuel pump does have a regulated pressure valve internally, set to around 5-6 psi. Actually it probably works like a mechanical gas pump, it pumps till the pressure builds against the diaphragm and stops it from pumping. The spring on the other side of the diaphragm is what sets the pressure.

 

[IDIBRONCO]

The only part of the return system that gets eliminated is the line that goes from the fuel filter head (or the line that feeds the IP depending on your set up) down to the cap on the #1 injector as far as I know.

 

[Grantly222]

Quick update on my situation- I did a visual inspection and found what looks like some very slight fuel wetness coming from the return lines somewhere at the rear of the engine passenger side (around #3 #4). Question- it seems like I could try replacing all the return lines first without taking the entire assembly out and see if the fixes it? Then if it doesn’t, I can proceed to replace more, but the lines would already be done. Any reason why I wouldn’t want to do this approach? Thanks burners!

 

[Cubey]

Quick update on my situation- I did a visual inspection and found what looks like some very slight fuel wetness coming from the return lines somewhere at the rear of the engine passenger side (around #3 #4). Question- it seems like I could try replacing all the return lines first without taking the entire assembly out and see if the fixes it? Then if it doesn’t, I can proceed to replace more, but the lines would already be done. Any reason why I wouldn’t want to do this approach? Thanks burners!

If the hoses are so old they are leaking, just take all the caps off and do the o-rings too. And do them all at once. It's pretty easy on truck.

If you want a challenge, do it on a van. I had to remove the fuel filter and alternator to reach the return lines on my RV. Also had to use this wrench in some places due to the angle needed on the injector line.

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[IDIBRONCO]

Any reason why I wouldn’t want to do this approach?

Yes there is. Once the o-rings are disturbed, it breaks their seal. Then you'll have A LOT of leaks. Next, you'll be pulling all of the caps off so that you can replace to o-rings, and you'll be kicking yourself for not pulling everything off in the first place.

If you want a challenge, do it on a van.

You forgot to mention that your van has a turbo on it. A N/A van would be bad enough.

 

[franklin2]

I agree with the others. In my experience the hoses rarely leak, its the o-rings. It's easier to make one side up complete with the hoses, and then slowly wiggle them all in position a little bit at a time. You might want to ask these guys what kit they use, I know some of them are having quality problems with the new plastic caps. I have redone my o-rings twice, and each time I have used my original caps with no problems. I just went and bought #111 o-rings and some fuel hose from Napa.

The first set of o-rings I bought from tractor supply in the hydraulic section of their store. They worked fine for about 5 years and then started giving my trouble with minor leaks. So I went with the viton o-rings from McMaster Carr and I have been good since.

 

[Cubey]

You forgot to mention that your van has a turbo on it. A N/A van would be bad enough.

The turbo isn't really isn't in the way for doing the return lines since it's in the middle. For the side-to-side crossover hose at the rear, I just used an extra long piece of hose, fed it across under the turbo/any heat shielding, connected it to the steel T on the drivers side, then cut it to length on the passenger side where it connects to a plastic return line cap. The walls of the engine tunnel are what are a pain on the passenger side and why I had to use that wrench, which I already had thankfully.

 

[rempfer]

I’ll take a crack at these. Cubey answered some of it already, but anyway here’s my take on it.
1). Another thing to remember about the IP is that it is cooled by the fuel flowing through it. The fuel returning to the tank is taking heat with it.
2). The fuel injectors have a valve inside that opens once the pressure reaches a set level. This is referred to as the pop pressure. As the IP sends fuel to each injector the pressure ramps up and then down. As the pressure is building, it’s not a problem for the injector to be closed. The incoming fuel is just building up pressure in the injector. Once the fuel reaches the pop pressure, the injector opens up and sprays fuel. The problem is once the pressure from the IP starts to drop off, the injector closes. There’s no longer enough pressure to hold the injector open, but there’s still fuel coming in that has to go somewhere. So it’s allowed to bleed off into the return lines.
3). I’m not aware of anyone selling products to eliminate the fuel return system. I know some of them claim to to eliminate some of the problems with the injector return caps, like machines aluminum return rails, or machined brass injector caps, but functional they work the same.

Thank you, Cubey and TNBrett. I believe I do understand the process now. You've made sense of it for me. Much appreciated!

 

[chillman88]

The only part of the return system that gets eliminated is the line that goes from the fuel filter head (or the line that feeds the IP depending on your set up) down to the cap on the #1 injector as far as I know.

This ^^^

I have done that on both my trucks and have not had any air intrusion issues. Even with a badly leaking return cap. Some people say it makes it harder to bleed if you run out of fuel, but I've had to deal with that before too and it hasn't been an issue.

 

[Cubey]

This ^^^

I have done that on both my trucks and have not had any air intrusion issues. Even with a badly leaking return cap. Some people say it makes it harder to bleed if you run out of fuel, but I've had to deal with that before too and it hasn't been an issue.

I had that deleted by just unhooking the hose from the filter barb, putting in a bolt and clamp on the hose, then using a scrap piece of hose on the barb with a bolt and clamp too (making it easily reversible), but somebody here said it might make things worse (or maybe it's just pointless) since I have an electric pump now, so I connected it back.

 

[chillman88]

I had that deleted by just unhooking the hose from the filter barb, putting in a bolt and clamp on the hose, then using a scrap piece of hose on the barb with a bolt and clamp too (making it easily reversible), but somebody here said it might make things worse (or maybe it's just pointless) since I have an electric pump now, so I connected it back.

To each his own. That eliminates any fuel drain back from the return lines by isolating them from the filter head. I've heard fuel cannot pass through the IP if it's off, although I haven't experimented myself.

Yes, your e-pump will re-prime the system, but if it doesn't NEED to you're better off in my opinion.