EFI return to fuel supply line

[browngr5]

Can I run the EFI return to a "T" fitting before my Low pressure pump. It's setup to feed a holly float and reservour right now, My high pressure pump circulates through my reservour and the float lets my low pressure pump add fuel as needed. The problem is the low pressure pump gets hot from not recirculating.

 

[DirtDonk]

Nothing wrong with T'ing it where you suggest, that I can think of.

Ok, was wondering if you even had a return currently, but just re-read it again, and it sounds like your return is there, but it's after the LP pump, so the pump doesn't benefit from the recycling. That correct?
If that's the case, then I don't see any reason not to re-route it back before the LP pump. I'm guessing it was probably more convenient initially to plumb the return to the reservoir? So yeah, T it in before your LP pump and you should be good.
I think that's the better way anyway.

Anybody else think otherwise?

Paul

 

[browngr5]

I wonder if the efi return feeds too much fuel to the "T" before the low pressure pump. It may backfeed through my tank selector. Another idea i have is to "T" and use a regulator to loop the LP pump back to itself to relieve dead head pumping.

 

[lonesouth]

That's a great idea. What about those with just a single HP pump and plumbing in just before the input to the pump?

 

[rustbucket]

I think you're going to end up with too much back pressure on the return line, and/or feed issues with the LP pump. I could be wrong. I would love to hear from somebody that has done it. I think the fuel from going into the T will either want to go to the pump, or back toward the tank. I believe at idle, more fuel diverts to the return line, which could cause the fuel to start flowing backwards. Especially if you snap the throttle shut. Basically, I think there will be a lot of turbulence in the fuel.

 

[lonesouth]

I don't see how the fuel could possibly flow backwards. There is no way that a larger volume of fuel is coming out of the HP pump than is going into the LP pump. After thinking some more, the only problem I see with this setup is that the fuel will heat without having a chance to cool down in the tank. Add an inline fuel cooler and I think that problem would be solved.

 

[BroncoDawg]

Lonesouth is right, could lead to vaporlock issues since fuel has no chance to cool.

 

[browngr5]

I think you're going to end up with too much back pressure on the return line, and/or feed issues with the LP pump. I could be wrong. I would love to hear from somebody that has done it. I think the fuel from going into the T will either want to go to the pump, or back toward the tank. I believe at idle, more fuel diverts to the return line, which could cause the fuel to start flowing backwards. Especially if you snap the throttle shut. Basically, I think there will be a lot of turbulence in the fuel.

I think your right, What should I do? Is anyone running 6 port fuel tank selector and running return into the vent lines to tanks? What is the

 

[DirtDonk]

I run a 6-port electric valve on mine. Haven't finished plumbing the return lines in yet, but they're going to go all the way back to the tank. To me it's the more elegant way of doing it. Not "required" per sé, but then you don't even have any questions about heat or turbulence.
I never bought one of the manual brass valves for that though. Was too lazy to cut a hole in my new floor pan, and thought it was a good idea to keep all the gas on the outside from now on!
And by now too, those brass ones are probably more expensive than an electric one.

Even though your method can certainly work (running it that way on a recent EFI I helped on), I say, when in doubt, go all the way back.
Since you're re-plumbing things anyway, it can't be that much harder to either T into an evap line in the tank, add your own barbed hose fitting to the tank, or somehow T into either the large fuel filler line, or better yet the filler overflow line (5/8 or so?).

That way there is no doubt.

Paul

 

[wdbowers]

we do this on hydraulic systems all the time to prevent cavitation when operating where high oil flow is needed such as a frontend loader. Deere on some newer diesel injection systems have a high flo transfer pump feeding the injection pump and tee off of the line from transfer pump and then back into the feed line through a restrictor to keep the transfer pump flowing instead of dead heading

 

[Broncobowsher]

The LP pump should only be deadheading as much as it would as if it were on a carbed application. Fuel consumption will be nearly the same either way.

I would look at a 3-port fuel filter (70's and 80's AMC and Chrysler come to mind) that has a return back to the tank. That was used to promote fuel flow and prevent vapor locking. I can't remember if they were simply orfice return lines or if they were bypass pressure regulators?

 

[Mark in Memphis]

I have not done an EFI swap yet, but I've heard different ideas about this.

1. Browngr5, you suggest that your low pressure pump is getting hot because it's not flowing enough fuel.

2. Some have said that when put the return into the tank, that their low pressure pump wore out because it was pumping too much fuel. Their reasoning was that a low pressure pump going to a carburetor would only pump the amount of fuel the engine was using. Whereas with a return line giong to the tank the low pressure pump was pumping fuel constantly.

I don't know what the correct answer is, but I hope you guys figure it out before I start my swap. ;D

Mark

 

[Broncobowsher]

That may have more to do with what kind of LP pump is used. An impulse type pump I could see burning out running without head pressure. While a vane type with an internal regulator (like Carter P4070) would run cooler as it isn't working as hard to build pressure. Also being fuel cooled would have more flow through it, staying cooler.

 

[browngr5]

This morning I ran the fuel rail return line to the rear tank but my Carter 1295S low pressure pump cant fill the reservour fast enough for the HP pump. I tried a big Holly LP high volume pump and it worked OK, the engine didn't have much power and burped once in a while. Since I ran the return line and had all the tools out I decided to remove the LP pump and reservour and relocate the HP pump. I put the HP pump down by the tank selector valve on top of the frame. Ran the HP 5/16 line to the fuel rail then ran fuel rail return line back to rear tank to one of the vapor 1/4" ports. I can still use both tanks once i find a manual 6port selector. Went for a long hot test drive and so far it works great. Not sure what will happen when the factory tanks get low on fuel. What do you all think?

 

[needabronco]

Some food for thought here. If you plan to run at altitude you will eventually have vapor lock issues and will eventually burn up your LP fuel pump. Several of us have had this problem. My theory is the LP pump is not designed to run at 100% capacity for hours on end, and over heats causing the fuel to get hot resulting in vapor locking the system. High altitude amplifies this issue, as the lower barometric pressure forces the pump to work harder. This cycle burns up the pump in short order. I burned up a LP pump in less than 300 miles!

I would suggest dumping the accumulator and plumbing the high pressure pump directly to the rear tank as close to the tank as possible, return the fuel to the rear tank. Use the LP pump as a transfer pump from the auxiliary tank to the main tank. This will also simplify your plumbing and wiring by getting rid of the 6 port valve and accumulator.

 

[Broncobowsher]

For all you people burning up LP pumps, what pump are you running? I think that is a key feature that is being missed. Can't lump all LP pumps together, there are different designs.

 

[Pedestrian]

Been running my Carter 4070 for over two years without burning it up yet.
I have had the high altitude fuel vapor lock issues though.
Maybe I'll try the high pressure pump only, on my trip to Colorado in July.

 

[73azbronco]

I would avoid returning fuel to pump intake for the only reason of vapor lock when hot (I'm in Az, surface of the sun right now at 114f).

I would return fuel to a T in the fuel tank filler vent line, the 1/2 inch ish line from fuel filler neck to tank.

Additionally, you might run into fuel pressure fluctuations if you feed the fuel pressure regulator return back to the pump.

While returnless systems don't have a return, they vent excess pressure back into tank as that is where the pump sits.

 

[Greg_B]

I had a lot of people tell me I needed a LP pump before my HP pump because the HP pump would not "pull" fuel from the tank.

It has been 11 years+ and I am still running the F250 external pump mounted to the frame under the passenger side door area. No LP pump and no accumulator. I ran this setup with both stock fuel tanks and a 6 way valve for years. I never had a single issue with pulling fuel even when low on fuel.

I did change the return lines several times to try and cut down on the vapor buildup. Somehow I thought the return line was creating the vapor by constantly stirring or mixing up the fuel. I put a T in the filler neck vent... I soldered a copper tube turned down the filler neck itself. I tried a T in the vent lines... I tried every idea everyone ever posted on return lines and venting the tanks... I just could not stop fuel from condensating in the vent line and dripping out on the ground or out of the charcoal canister.... Or at times pushing out the filler cap. I drilled holes in the cap... tried vented and non vented caps...

I even built a new stainless steel 23 gallon tank with a series of bungs welded in it for pick up, vent and return lines.... Nothing worked...

Until.... I went to the junk yard and got a new charcoal canister and solenoid purge valve and installed just like factory... no more fumes or fuel condensation.

Greg