Simple auxiliary fuel tank mod and EFI

[Cafireman07]

Am I being too simple minded, or is this a good idea? I am upgrading 71 bronco with a Holley Sniper EFI and I would like to maintain use of my auxiliary fuel tank.

Is it possible to attach an open direct fuel line from your auxiliary fuel tank with the main tank and have them function effectively as one tank? Given that the main tank sits lower than the auxiliary tank, but the gas fill spouts are at the same level.

These are my thoughts:

1. Given that the tanks are connected, when you fill the tanks, the fuel level will passively fill to an equal level in the fuel fill spouts. It may take a minute or two, but it should equal out.

2. When you drive your bronco, fuel will be taken from the main tank to the engine. The fuel from the auxiliary tank will passively gravity flow to the main tank until the auxiliary tank is empty.

3. When the auxiliary tank is empty, you would then operate with the remaining fuel in the main tank.

I understand that many people like to provide a fuel line with a fuel pump and pump fuel from the auxiliary to main tank. I am wondering if this is necessary.

I have a 71 bronco with a 4 speed manual top loader. I plan to put in a Holley Sniper EFI with the no fuel return feature.

I have asked some of the efi experts at some of the early bronco venders, and at Holley. The early bronco guys seemed kind of stumped because it was so simple, but were unaware of anybody trying it. The Holley guy was not familiar with early bronco two tank system.

I’m throwing this out there and hope to find some additional input.

Thanks.

 

[blubuckaroo]

Welcome to CB Cafireman07.
I don't know if that question has been raised, but I can't see why it wouldn't be worth a try.

 

[DirtDonk]

Even some factories did it, both with cars and motorcycles with two tanks on either side of the frame.
One possible negative is that some people cite their aux tank as a backup in case their main develops a leak or the in-tank pump fails.

In the case of an in-tank pump failure, you'd need to have a backup high-pressure EFI pump somewhere anyway. So extra plumbing no matter where you look.
In the case of a catastrophic leak you'd drain both tanks if they were connected like you suggest. But that's seemingly more for off-roading Broncos, and might not be such a big concern on the street. Which is where most Broncos find themselves these days anyway. So not much of a problem for most of us.

Which just leaves the dilemma of plumbing it. Something that not many like to do, which is probably why it has not come up before.
Then again, with equalized crossover tubing, what happens when your full 11ga tank decides to let gravity have it's way and try to push a few gallons into the 7ga aux tank and then out the filler neck on to your nice new paint?
Maybe this can be taken care of with a 1-way baffle/valve thingy. Or maybe it's not an issue in the first place?
Are the tops of the tanks of equal height? If you're parked on a hill facing down, is the main tank going to drain it's life out into the aux tank?

Paul

 

[Cafireman07]

Thx, blubuckaroo and DirtDonk. I have to agree, plumbing is never as straight forward or as easy as it seems it should be, in your house or your car. I am a smart enough mechanic to know I’m not that smart.

I’m going to give it a try. It just seems that this possible solution is too good and simple to be true. It seems that someone should have tried this before.

I’m still open to more input.

 

[DirtDonk]

Be sure to take pics and document it for the rest of us. Very interested in how it turns out. Especially the parts about attaching the fittings to each tank and such. Plastic for the aux and steel for the main unless you have a '77.

Are they both still original style tanks?

Paul

 

[sprdv1]

Am I being too simple minded, or is this a good idea? I am upgrading 71 bronco with a Holley Sniper EFI and I would like to maintain use of my auxiliary fuel tank.

Is it possible to attach an open direct fuel line from your auxiliary fuel tank with the main tank and have them function effectively as one tank? Given that the main tank sits lower than the auxiliary tank, but the gas fill spouts are at the same level.

These are my thoughts:

1. Given that the tanks are connected, when you fill the tanks, the fuel level will passively fill to an equal level in the fuel fill spouts. It may take a minute or two, but it should equal out.

2. When you drive your bronco, fuel will be taken from the main tank to the engine. The fuel from the auxiliary tank will passively gravity flow to the main tank until the auxiliary tank is empty.

3. When the auxiliary tank is empty, you would then operate with the remaining fuel in the main tank.

I understand that many people like to provide a fuel line with a fuel pump and pump fuel from the auxiliary to main tank. I am wondering if this is necessary.

I have a 71 bronco with a 4 speed manual top loader. I plan to put in a Holley Sniper EFI with the no fuel return feature.

I have asked some of the efi experts at some of the early bronco venders, and at Holley. The early bronco guys seemed kind of stumped because it was so simple, but were unaware of anybody trying it. The Holley guy was not familiar with early bronco two tank system.

I’m throwing this out there and hope to find some additional input.

Thanks.

Welcome aboard Cafireman07....

 

[sprdv1]

Be sure to take pics and document it for the rest of us. Very interested in how it turns out. Especially the parts about attaching the fittings to each tank and such. Plastic for the aux and steel for the main unless you have a '77.

Are they both still original style tanks?

Absolutely.....

 

[Cafireman07]

It’s going to be a bit until I have the time to do the upgrade, but I will try to provide pics. Thx

 

[GreMac]

Cafireman07 I was actually thinking of doing the same thing when switching over to a Sniper. The thing that kept me from doing it were that it seemed like the fuel line connecting the two tanks would have to be completely below the lowest desired fuel level in order to transfer from one tank to the other since it wouldn't be possible to maintain a syphon in the line. That meant it would be hanging a few inches below the frame and not far above the axle housing.
I ended up going with a surge tank that I mounted in the engine compartment so I could keep the dual tanks and not have to go to twin electric pumps mounted in the tanks or near them. I am anxious to see how your setup turns out, like someone already mentioned its a common method in all kinds of vehicles, just a question of whether or not the vehicle setup and tank configuration will allow it.

 

[bteutsch]

I have a Fitech system on my 1971 Bronco, I run two frame mounted pumps, one mounted very close to the Auxiliary tank and one near the Main tank. Both Fuel pumps are mounted on the outside of the Drivers side Frame. I ran the fuel lines together using a threaded Y fuel connector. I have a check valve on each connection. The lines come together and run to a EFI fuel Filter, from the fuel filter the line continues to the Throttle body fuel inlet. I used the original fuel hose for the return lines that feed backwards through the original fuel selector valve. I added Moroso return ports in each tanks fill hose. I use a relay and the original electric fuel gauge selector switch to change tanks/fuel pumps. I like this set up for two reasons, One everything appears stock as you flip the selector switch on the dash to choose which tank the fuel gauge reads just like stock procedure it also changes what fuel pump is active, you then change the mechanical valve under the seat like you would originally it just chooses which tank to return to now. And the second reason is for redundancy. If one fuel pump were to die I have a spare on the other tank. The fuel pumps I used are off the shelf for a 1985 F150 with EFI.

 

[Broncobowsher]

The only way your plan would work is if you filled the aux tank into the filler neck and hope there is enough static pressure to push fuel through your transfer tube and start a siphon. If at any time you get an air bubble or either end of the siphon catches air the transfer will stop. In short, you would need to modify the main tank to have a bottom inlet off the transfer line of the aux tank. Connecting at the top of the main tank will not transfer fuel.

You may be a bit confused by the no return line. The Sniper will not work with a dead headed fuel pump. It is a fixed (58.5 PSI) fuel system. Any EFI pump that can make that pressure has a regulator and a return to the tank. Even the in tank pumps have an in tank regulator so there is just a single line to the EFI. Having a looped (return style) fuel line is good for EFI. It circulates cool fuel through the injectors and in this case the computer is in the same throttle body as the injectors that are being cooled. OEMs don't do it that way anymore because it heats the fuel in the tank and makes evaporative emissions more difficult to manage.

If you really want to run a single feed fuel system the Sniper will support it. But there still needs to be a regulator involved somewhere. Corvette LS1 fuel filter is really cool part as it combines a good filter with a regulator.

One thing you can do is run a high pressure pump off each tank into a common filter. Since high pressure pumps contain a check valve to keep the system charged when the engine is off (easier engine starts) you only get fuel out of the pump that is energized. The other pump is dormant, check valve prevents backflow. Done right you can just return all the fuel to the main tank via the return line when running the aux tank.

 

[Rustytruck]

I would check your fuel cap for proper venting allot of caps will vent under suction but they dont really vent unless there is some form of suction on the cap. the valve in the cap is pretty sensitive. for free flow you will unrestricted free flow venting. then there is a full rear tank there is head pressure due to the weight of fuel in the tank. it is not as simple as you think. and little things can get in the way of working the way you wish it would. All you can do is try it. so if the added side tank keeps the rear tank full where is the return fuel going to go?

 

[markw]

Thanks for bringing this up. Two tanks and FiTech here as well.
How would I plumb this as an aux tank to main tank system not meant to run off aux tank? Sorry for the hijack


Sent from my iPhone using Tapatalk Pro

 

[ba123]

I know this is an old thread, but as an FYI, when I originally installed my mustang 5.0 EFI, I used both tanks with a frame rail mounted pump and an electronic fuel tank source switch and it worked great. I might still have the switch paying around...maybe or might be able to find the info if anyone wants to know.

 

[DirtDonk]

Of course!
Every time some pertinent info is posted up it benefits somebody, now or in the future.
So yes, definitely.

Thanks!

 

[ba123]

I really cen't believe how much stuff I saved from this project sooooo long ago.

Anyway, the part used was Napa Fuel Selector Valve 2-2198, found here: https://www.napaonline.com/en/p/CRB22198

And the fuel pump I used was AFP E8228.

I am pretty sure I still have both, but certain I at least have the pump if anyone is looking.

 

[sprdv1]

I know this is an old thread, but as an FYI, when I originally installed my mustang 5.0 EFI, I used both tanks with a frame rail mounted pump and an electronic fuel tank source switch and it worked great. I might still have the switch paying around...maybe or might be able to find the info if anyone wants to know.

still great info