Twin fuel tanks and EFI returns

[CA650]

I’ve though about doing some engine upgrades.

Has anyone seen a clean solution for pumps and return lines for EFI when there are twin tanks?

I probably wouldn’t even mind upgrading the tanks themselves but I don’t know what to do with the return lines and the cut over lever beneath the seat. I was hoping to keep the twin tanks, lever etc the way it is.

Whenever I think about an engine upgrade - I talk myself out of it. Usually it’s because my current stock engine runs great, leaks a little coolant, gets bad mileage but otherwise runs great with its Holly 4brl.

I still think of doing the top end or a crate engine with EFI - maybe the gt intake or a crate or roller cam conversion. Or whatever..

Whatever path i think I’d like to go with EFI and the real sticking point is that I think all the good EFI setups require return lines and I didn’t like any of the hacks that have some gas reservoir in the engine bay.

Has anyone ever worked that out or does everyone with EFI go with just a single tank.

 

[CA650]

Maybe found my own answer I missed this thread in my search
https://classicbroncos.com/forums/showthread.php?t=29831

 

[Broncobowsher]

So many ways to skin this this cat.
The 6-port EFI valve is a long running standard solution.
Ditching the aux tank and going with an oversized main tank is popular as well.
Run the aux tank with a transfer pump to the main.
Run the aux tank and have all the return go to the main.
The latest solution I am currently running, a high pressure pump per tank. Post pump check valve (redundant to the in pump check valve) that Tee together into the filter and to the EFI. The return is done via a standard 3-port low pressure fuel selector solenoid valve. That solenoid is tied to the Aux pump. A toggle switch selects main tank and default main tank return, or switches to the aux tank and energizes the selector solenoid to return to the aux tank.

Now if you want to throw an accumulator into the mix, even more options.

 

[spap]

The duel high pressure fuel pumps is a good idea, if one pump goes bad you have a back up
I was just going to run a transfer pump the the 23 gal main but I like having an extra pump

 

[suckerpunched]

I ended up with a single EFI tank. But what I was going to do was to run two high pressure pumps. for the return, some years ago I had an old tractor with a gravity fed carburetor that would flood out when parked. I installed an electric fuel shut off in line that cured the problem. It was an inline valve with a solenoid that had two wires coming out of it. with 12v applied it would open. So... I figured I would buy two, one for each tank run the returns through them and pull power to open the valves from the fuel pump for that tank. So when a fuel pump was running, that tanks return line would be open. Like said before, lot of ways to do it, but thats how I was gonna skin the cat.

 

[CA650]

So many ways to skin this this cat.
The 6-port EFI valve is a long running standard solution.
Ditching the aux tank and going with an oversized main tank is popular as well.
Run the aux tank with a transfer pump to the main.
Run the aux tank and have all the return go to the main.
The latest solution I am currently running, a high pressure pump per tank. Post pump check valve (redundant to the in pump check valve) that Tee together into the filter and to the EFI. The return is done via a standard 3-port low pressure fuel selector solenoid valve. That solenoid is tied to the Aux pump. A toggle switch selects main tank and default main tank return, or switches to the aux tank and energizes the selector solenoid to return to the aux tank.

Now if you want to throw an accumulator into the mix, even more options.

Thanks

I would like to understand this better. I had assumed there would need to be two fuel pumps one per tank. I’m having trouble picturing how this is wired and the plumbing. I’m not sure i understand what a check valve is or why there would be redundant ones.

Mike

 

[Broncobowsher]

Thanks

I would like to understand this better. I had assumed there would need to be two fuel pumps one per tank. I’m having trouble picturing how this is wired and the plumbing. I’m not sure i understand what a check valve is or why there would be redundant ones.

Mike

Each tank gets a pump. The output of both pumps is combined. Most high pressure pumps have a check valve built into the outlet, keeps the fuel line charged with fuel so the pump doesn't have to re-prime after sitting parked. I ended up with check valves screwed into the outlet of the pumps, something I later realized was redundant.

Comes down to one pump running and supplying fuel to the engine. The other pump is off and the check valve prevents fuel from flowing backwards through the pump and into the other tank.

No selector valve is needed on the supply side, it is all automatic with the check valves. The selector valve is only needed on the return, so the fuel goes back to the tank that it is being drawn from. Mine is wired so default (non-energized) the return is the main tank. Activated (energized) return is the aux tank. To energize, power is pulled from the aux tank fuel pump. When that pump is on, that is the matching return.

I've been running this since spring.

 

[blubuckaroo]

Broncobowsher, that's a great option!
Way better than eliminating the aux tank or the transfer pump options.
The transfer pump option has some serious safety risks.

 

[Broncobowsher]

I also thought about various failure scenarios.
If one pump dies, use the other tank. Might require a little side of the road/trail siphon and refill or move some hoses around.
If a check valve leaks, it will probably be minor, some leakage back into the other tank. Major failure, same. That might take a pair of vice grips to clamp off a line.
Return solenoid fails, returns to the wrong tank.
If you are having a failure that is causing a tank to overfill, switch to that tank and run it. Once low, go to the other tank and let the internal leakage occur. Go back to the filling tank and run it more.
Overall the failure modes are not that severe. Worst would be an overfilled tank and it's hard to eliminate that on a multi-tank fuel system. Even so, you still have a full tank of gas.

The single tank really is the simple way of doing it. But if you have to have 2 tanks...
I'm running this on a 460 powered F250 that got a Holley Sniper. I thought about the single 38 gallon tank option but didn't want the spare to end up in the bed. To keep the 40 gallon capacity it had to be both tanks. With a 460, you need the 40 gallons.

 

[Z Bronco]

When I put EFI in my Bronco I used a 23 gallon main tank with the fuel pump in the tank (early BCB tank), I have a Carter external fuel pump for the auxiliary tank with a tee into the return line for the main tank. I had to put in a check valve in this line as fuel would go past the Carter pump and into the aux. tank, the check valve solved this. My aux tank is now a big fuel can which I needed for long trips. I have a safety toggle in the dash to prevent accidental filling of the main tank. Very little plumbing and works well.

 

[Broncobowsher]

When I put EFI in my Bronco I used a 23 gallon main tank with the fuel pump in the tank (early BCB tank), I have a Carter external fuel pump for the auxiliary tank with a tee into the return line for the main tank. I had to put in a check valve in this line as fuel would go past the Carter pump and into the aux. tank, the check valve solved this. My aux tank is now a big fuel can which I needed for long trips. I have a safety toggle in the dash to prevent accidental filling of the main tank. Very little plumbing and works well.
View attachment 485099

The transfer pump has an issue I don't like, running the pump dry.
What I did in the past is very close to what you are doing. Difference was the engine RAN on the aux tank and all the return was to the main. If you run the aux tank completely empty the engine stalls. Switch to the main and keep going. This was to prevent running the aux dry. You can run the tank dry, but you would be hard pressed to run the pump long enough to burn it up.

I had also thought about putting some switching. A microcontroller to read the float level (difficult while also using the stock gauge), a pressure switch, which would need a restriction to create enough backpressure for the switch to see which would reduce the flow rate. None of those satisfied me being they were too complex for a simple system.

 

[CA650]

Those are good options. Do you feel like you need the extra check valves now that u understand that the pumps do this themselves?

What brand/model of pumps and check valves did you use I’m curious?

Now that I’ve listened to this and thought about it some more. I’m again thinking I just leave the old girl alone and if I want to mod something, I should probably do it on a different bronco, go with the singe tank and do the whole project ground up.

I’m thinking of messing with something that isn’t broken yet but will be someday.