EFI with 3 fuel tanks?

[DirtDonk]

One way of ensuring you don’t overfill a tank is to run the one you’re going to fill almost completely dry before you start transferring. If the transfer tank is smaller than the one the gas is going into, the only problem you should have is burning out the pump if you leave it on after the tank is dry.

As with almost everything on these older vehicles, the responsibility lies with the operator to pay attention to what they’re doing.

 

[Steve83]

What if I tied aux 1 and aux 2 together to a LP fuel pump to a switch to just feed the main tank when it gets low?

How would you/he or the pump or the valve know when a tank is low enough to accept more fuel; IOW: how would anyone know when it's actually full?

The simplest, safest answer is to return fuel to the tank it came from, using 2 6-port valves as Oldtimer suggested.

If you absolutely have to return fuel to 1 tank, then you have to create a LARGE overflow system (capable of gravity-flowing slightly more than the pump can possibly move) from the return tank down to each other tank (so that, if the 2nd tank overfills, it flows down to the 3rd).

But any 3-tank system creates the question of how to FILL the 3rd tank... Will there be a 3rd filler neck? Will it be on the same side of the truck as the first 2 so they can all be filled at the gas station? Or will one be on the other side? If only 2 fillers, then you need an even-larger overflow between 2 of the tanks, capable of handling more than a gas station pump can flow (which means a fullsize Y in the filler neck). Where will all of this plumbing run? There's not a helluvalotta extra space in the eB's quarters.

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[bronco italiano]

Thanks Steve for the input.
-3 tanks, each with a filler neck
-Switch would be required to activate/deactivate the transfer pump.
-Current main tank fuel sending unit is active so that would be the only tool to say, "Tank is low I will send over some fuel".
-Does that make any sense? I feel like I am missing something.

 

[Oldtimer]

- He insists on having the 23gal main and 2 saddle tanks.
-My buddy insists on retaining the factory fuel tank valve
BI

Clarify the statring setup of fuel system.
There are 3 fuel tanks.
Factory fuel tank valve was for 2 tanks.
How was third tank plumbed?
Starting setup has one low pressure fuel pump sucking from the three tanks (thru selector valve)?

 

[DirtDonk]

I’ve heard that the factory valve cannot handle EFI pressures, so that’s something to think about as well. Not sure if that’s the case, but I don’t know of anyone who has successfully done it.
Maybe someone here knows for sure.

The easy solution for both, however, is to leave the factory valve in place in the floor, and just not use it. You get the look, but don’t have to worry about its function.
Leave it disconnected from any fuel duties at all and install two EFI ready Electric valves with return lines and let the switching duties be done by the gauge selector switch on the dash. Still stock, but instead of just the gauges it also switches the tank location using one of the two valves. The other one is done through a switch that turns on the low pressure transfer pump.
Or better yet, since the third tank will not be in the EFI system, you can use the factory valve for that.

 

[Steve83]

Switch would be required to activate/deactivate the transfer pump.

If it was a countdown-timer, you could choose how long to run it to reduce the chance of overflow or running dry. But if it were a momentary switch triggering a latching relay with a normally-open pressure switch holding the relay latched, that would at least prevent running dry which could damage the pump. Overflow is at least as important, since it wastes money, and pollutes, and can set the whole vehicle on fire.

Current main tank fuel sending unit is active so that would be the only tool to say, "Tank is low I will send over some fuel".

How would you know if there were any fuel in the other tanks to send, or which one had some? You might think there was auxiliary fuel, only to run dry when you need it.

I feel like I am missing something.

You might be missing how critical the physical geometric arrangement of the tanks, vents, valves, & overflow hoses is. It must continue to work when the vehicle is in-motion, at extreme tilt while off-roading, AND when rolled over. Just making the right connection from one point to another isn't enough - the exact routing of some of the hoses matters.

And the original tank valve can NOT handle EFI pressure. It's designed for suction, or just the weight of gas above it, at the most.

 

[bronco italiano]

Clarify the statring setup of fuel system.
There are 3 fuel tanks.
Factory fuel tank valve was for 2 tanks.
How was third tank plumbed?
Starting setup has one low pressure fuel pump sucking from the three tanks (thru selector valve)?

If I can tie the 2 auxiliary tanks together to "feed" the main tank via LP fuel pump, there should be no need for a selector switch, as everything going to the engine is from the 23 gallon main tank with LP pump to engine compartment HP pump to EFI. I would also route the return line to the main tank. It is up to the operator to be aware of when the tank is near full. The 2 auxiliary tanks have no appropriation for fuel sending unit. My buddy would do the classic, run it dry and switch the selector, but that is a bad idea for sure with elec. fuel pumps and EFI.

 

[bronco italiano]

If it was a countdown-timer, you could choose how long to run it to reduce the chance of overflow or running dry. But if it were a momentary switch triggering a latching relay with a normally-open pressure switch holding the relay latched, that would at least prevent running dry which could damage the pump. Overflow is at least as important, since it wastes money, and pollutes, and can set the whole vehicle on fire.


How would you know if there were any fuel in the other tanks to send, or which one had some? You might think there was auxiliary fuel, only to run dry when you need it.


You might be missing how critical the physical geometric arrangement of the tanks, vents, valves, & overflow hoses is. It must continue to work when the vehicle is in-motion, at extreme tilt while off-roading, AND when rolled over. Just making the right connection from one point to another isn't enough - the exact routing of some of the hoses matters.

And the original tank valve can NOT handle EFI pressure. It's designed for suction, or just the weight of gas above it, at the most.

The overflow and running dry are concerns I have and the operator will have to be very aware. He is generally very good about maintaining fuel in his tanks though.

The tanks were very old school aux tanks. My buddy used to work at K-Bar-S after his time in the Marine Corps (late 1980's). I suggested one 23 gallon tank, but Marines prefer 50 gallons of fuel for an extended trips and he doesn't have access to the KC-135 Stratotanker since he left the Corps.

Since I plan to have 0ne tank feed the engine the valve will be deleted.

 

[Steve83]

He is generally very good about maintaining fuel in his tanks though.

But the whole purpose of the transfer pump is to EMPTY the tank it's in. So it always needs to run "dry", but not a second longer. That's why the pressure-latching relay would be a good circuit design. If the tanks are plumbed properly with an overflow draining back to the previous tank, you could even set it up to be fully-automatic. Make both transfer pumps latch on during cranking, and unlatch if their output pressure is <2psi. They'd constantly circulate gas toward the "main" tank until they run dry, and then automatically stop pumping until the next startup. If they're still dry, they'd shut off immediately. No operator action (or even AWARENESS) necessary.

 

[bronco italiano]

Steve that is slick!! How do I search this type of system?
-On your diagram, is the single supply pump (carb or efi) the one I want to do?

 

[Geiri]

Here in Iceland we have lot's of tanks. The usual way is to have auxiliary low pressure fuel pumps, pump the gas back to the main tank if is it's getting low.

 

[Steve83]

How do I search this type of system?

I don't know that you can - I just imagined it. But if you document it well, OTHER people will be able to search up what you do.

On your diagram, is the single supply pump (carb or efi) the one I want to do?

Yes, but the main would be the hi-pr.EFI pump, and there would be 2 transfer pumps. But instead of the momentary transfer switch shown, there would be a separate latching relay for each transfer pump; and each relay's circuit would include a very-low-pressure normally-open fuel-tolerant switch where this shows the OFF switch. The ON switch would be the I (ignition) output of the starter relay (which would not be connected to anything else after the EFI conversion).

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This shows how to add electrical accessories:

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This explains how to size fuses & wires, and how grounding works:

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[bronco italiano]

Steve that SuperMotors site is really great.
Do I need special permission to sign up?

 

[DirtDonk]

That’s a good question. Sometimes the pages won’t load for me at all. Other times they snap right open when I click on his links.

 

[Steve83]

Steve that SuperMotors site is really great.
Do I need special permission to sign up?

No, but for some reason, I haven't been able to upload anything new for a few months. IDK if Dana changed some settings that only affected my old/large/free account, or if something has happened that will prevent anyone from uploading. And he hasn't answered my email. Let us know what happens when you try to start an account there & upload pics.

This is a really-old thread with step-by-step instructions:
www.supermotors.net/forums/thid-5972-how-do-i-post-pictures-sounds-and-or-videos

 

[El Kabong]

No, but for some reason, I haven't been able to upload anything new for a few months. IDK if Dana changed some settings that only affected my old/large/free account, or if something has happened that will prevent anyone from uploading. And he hasn't answered my email. Let us know what happens when you try to start an account there & upload pics.

This is a really-old thread with step-by-step instructions:
www.supermotors.net/forums/thid-5972-how-do-i-post-pictures-sounds-and-or-videos

I just checked. My last upload was Dec 2, 2022. I could load a single pic that day, but couldn't add any more.