If you didn't offend someone did you even internet?

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Yep, I understand. When I said "I know this is to SWAP tanks, not to have an AUX tank." I meant the thread in general. Not your kit. When you started this thread last year, I had the tank in my Amazon Wishlist up until about a month ago. I would really like to do this so I could take the Jerry Cans off the bumper. But right now, it's not time and cost effective. I have too many other projects I need to finish. LOL

Keep up the great work!

Well @psraff . This fuel thank that we are using is actually an Aux Tank to an F-series truck. So, there must be a simple, effective and stockish solution to your idea. The F-150’s have a fuel selector switch and valve assembly that allows you to switch back and forth between the two tanks. Figure out a way to incorporate those items into your plan, and you’ll be able to have dual tanks that can be accessed with a flip of a switch.

https://www.1aauto.com/fuel-tank-sel...e/i/1afmx00113

https://www.am-autoparts.com/1994/Fo...iABEgI4PvD_BwE

Forgive me Steven, I can't remember whose thread it was that used the external Carter fuel pump to transfer fuel from the aux tank to the main tank, which is what I really want to do with this setup and DIY rear bumper with integrated hitch and fuel fill.

The need for a secondary fuel gauge isn't as great when it's an auxiliary tank and I believe an idiot light could be wired up off the aux sending unit to indicate when the aux tank is low or empty. Maybe even a Dakota Digital gauge in lieu of the stock clock, for those crafty enough with a big enough budget lol

I'm all in on this mod

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@octanejunkie I think that was @Dirtco

Idk if having all that extra stuff would be worth the extra re-engineering it would take. I’d think using factory switches and valves would be less work and everything would be as simple as flipping a switch once one tank gets empty. It would just turn one pump off and the other on. Easy peasy. No issues with one tank filling another, external pumps, and venting issues that go along with it. Ford already engineered the dual tank setup, might as well just take those pre-engineered pieces and make it work for your benefit.

Okay

But dual fuel gauges?

I think the Ford setup has a switch to alternate senders and use the same gauge, IIRC...?

There's still the issue of the Toyota gauge reading the opposite of the Ford sender, though (although I like the sender float arm modification angle...)

Now please note, I don't know a dang thing about this stuff.... But when I was thinking about this as being an Aux. tank I was thinking along these lines:

1. Drop original tank and weld several bungs on it.
a. one to run the vent from the aux. tank.
b. one to run from the fuel pump that's in the aux. tank.
2. Mount the aux tank just like people are doing it with the pump inside like normal.
3. Wire that pump to a switch and relay
4. Connect the fuel and vent lines between the two tanks
5. Figure out how to fill the aux tank
a. would be great to use the original fuel fill to fill both tanks
b. maybe some kind of dump valve that changes flow at the 'Y' that splits to the two tanks....
c. really have no idea.. just spitballing.

One question with this is we look at fuel pumps in PSI. But what is the VOLUME? How many gallons per minute (or minutes per gallon) would a Ford fuel pump run at?

But you're right. Many trucks have had duel tanks. Why re-engineer the wheel (or in the case, the fuel tank).

GMC Duellies ('70s) had duel tanks and and I'm pretty sure it had one gauge. I remember as a little kid flipping the switch and watching the gauge going from Empty to Full. But then again that truck used to be an Ambulance up on the Slope so maybe it was a special order thing.

If I did end up doing this as a swap, I know I would love to keep the original fuel gauge just because having something not work in the dash would bug the hell out of me.

same here - I think this stuff is solvable with a couple of weekends to throw at it.

Also, just got word from my cut & bend shop that the mounting kits will be done on 7/31 (projected.)

so yeah, this is happening.

After reading Shannon's questions, and the more I think about the dual tank/tank select switch (a switch to divert the power from sending unit #1 to sending unit #2) and then dual gauge wiring and impedance matching the ford sending unit to work with the Toyota gauge (not impossible, but work) the more I think each tank should be as independent as possible, including dedicated fill and vent lines (not integrated with the Toyota plumbing) as well as perhaps a second fuel gauge for sheer simplicity. Personally I would not modify the Toyota tank by adding extra bungs/vents as not to mess with the evap system or create a leak/liability.

The Tank Selector Valve Steven linked says 65 PSI max (EFI compatible) and the Ford tank will need a commensurately capable EFI compatible in-tank pump, OEM Ford or top quality aftermarket, not Spectra brand. I have plumbed and installed an EFI from scratch system before and while it's not rocket science, a 3/8" fuel line and 5/16" return is standard along with a fill-neck integrated vent and vented/pressurized cap. Most factory EFI systems require between 50-60 psi continual, and asl long as we flood the fuel rails we are good, excess fuel will return to the tank via the return line. FWIW, I prefer an in-tank pump to an external for many reasons.

The Dorman Fuel Tank Selector Switch is going to need to be wired correctly, and while Dorman does not include a pinout map, I found this diagram online. I am sure the wiring pigtail is sourceable somewhere, I've not checked yet



Here is a Chevy diagram that shows the wiring through the Selector Valve, for entertainment purposes.



For all intents and purposes, I prefer Chevy wiring and electronics over Ford, so here is the same Selector Valve from Delco that includes a wiring pigtail for the 6-pin connector https://www.1aauto.com/fuel-tank-sel...0/i/1azma00006 btw only 5 pins are used on the valve and 4 on the Checy switch, according to the Chevy diagram linked and other references I found online. The 6 pins on the Ford switch may be power switching between the two fuel pump relays, which makes for more splicing and dicing into our wire harnesses.

IMO, the trick with the aux tank will be where to position the fill-neck and vent -we want it higher than the bumper. The problem with a low-mounted fill and shallow fill neck angle is that on steep ascents fuel will retreat down the fill neck and will pool against the inside of the cap. If using an integrated fill/vent cap scenario (required in CA to pass smog) you can't block the vent with fuel or the aux tank won't be able to vent. The best place for the aux fill may be hidden in the passenger side wheel well where no SMOG test tech will think to look for it, as high up as possible to allow proper venting by not becoming a fuel retreat path.

Another note worth mentioning is that many Ford trucks run the vent and fill in the same tube, a smaller 1" tube is inside the largest 2.25" tube, the outer tube being the vent and the smaller is the fill. This is not an easy scenario to recreate, I've tried. Fuel safe hose is expensive and rigid, not easy to work with. This is why the Ford tank we are looking at, as well as the Ford factory sending unit/pump plates only have 2 nipples, pressure and return, venting is integral with the fill. FWIW, Ford Ranger pickups (and other Ford pickups probably) have a nice side fill tube inside a tube, flattened to pass between the frame rail and bed, that we might be able to use but will need to extend it to get to the wheel well.

Just sharing some experience. Looking forward to what others have done or will come up with. Happy to help with this in any way.

why? venting? a single fill neck to a Y would be very elegant; assuming no vent issue to overcome?

No kidding - the Ford Multi-mess switch/relay thing is confounding.

Think about every dual tank truck one the road. They all have separate fill necks. Two tanks, two fuel doors, two gas caps. I'm betting it was designed this way for idiot proofing and simplicity. The problem we will face is our trucks never had dual tanks. So, we either come up with a place to run the other filler neck or create a y-pipe with a turn fitting to direct the fuel to the correct tank.

The first solution just requires a good spot for the fill neck of the new tank. The second requires modding the existing fill neck. To do that we'd need a flapper valve centered in the OEM fill neck. Not impossible but it'd be pretty hard to do and maintain tank pressure. The pin that would be needed for the flapper valve would need to be drilled through the filler neck. How would that hold pressure?

Has anyone looked into the ECU wiring for the stock fuel pump and fuel gauge? We could easily stay with one gauge as long as we can fool the ECU into using the other tanks pump and gauge. It should work like any other factory dual tank set-up. You tell the ECU to shut off one tank and read the other. As we all know what works in theory can be a real PIA in practice.

@theesotericone
I think it could be done without having the ECU involved in any decision-making. Intercept the wire that powers the fuel pump relay and jumper to the pump power input port on the switch, pre-relay. Jumper the output on tank A back over the wire you intercepted back to the main fuel pump relay, then run the output of the aux pump (tank B) off the switch to a second relay that powers the aux fuel pump off it's own fuse.

This way the ECU still "controls" power to both fuel pumps, the main pump through the main fuel pump relay and the aux pump through the secondary relay, toggled by the switch.

Simplicity says use the aux tank's pump to transfer fuel to the main tank on demand (T fitting in the main fill line) and run it off a switched relay exclusive of the main pump. Figure out the aux fill and vent and put an aux tank fuel gauge somewhere out of the way and be done.

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