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Old 01-04-2006, 09:42 PM
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Dual gas tanks with EFI

I have a 78 chevy 4x4 with dual 20 gallon gas tanks. In a couple months I want to switch it over to tbi efi. I think I've got a pretty good idea of what needs to be done, except for the fuel tanks.
I want to keep both tanks because the truck will be used for hauling long distances and I need the range.

What I'm not sure of is what the best way to incorportate electric fuel pumps. The way it is now there is a switch in the cab that operates a solenoid that switches the fuel pickup from one tank to the other. I'm not sure if this will work under the higher pressures of an electric pump. I'm also not sure if there is a fuel return line from the mechanical pump; I don't think there is. I'll take a closer look.

I guess these are my options:

1. Put an in-tank pump in each tank. Have the appropriate pump turned on when the pickup is open to that tank. Somehow make the return line empty into the appropriate tank.

2. Put a single external in-line electric pump after the solenoid switch. The pump would then have to pull the fuel out of the tanks, through the switch, and then push it to the engine. I've read electric pumps don't like to pull fuel, only push. Would this work?

3. Add a third small auxillary tank. I've read some fords had this. Place low pressure pumps in each main tank and have a high pressure pump in the smaller third tank. The fuel would be pumped out of one of the main tanks into the aux tank. I guess all fuel would be returned to the main tank being used?

4. Take out the dual tanks and swap in a large single tank. I don't know if this is possible. I don't think there's room. It would be nice to put a big single tank off a 90's 2500 but they were placed on the other side of the frame rail and I don't think my truck will have room. Anybody know of a swap?

Other's must have converted these trucks to efi, but I have found very little information out there for these dual tank trucks. Any help is appreciated.

81 Grand Prix, 355, 700r4, 8.5" 4.10
64 Oldsmobile Jetstar, all original
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Old 01-04-2006, 10:04 PM
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one fuel pump in each tank, tank one feds the engine, tank 2 pumps fuel into tank one, the return from the engine goes into tank 2

if you set up tank 2 so that the fuel pump shuts off after it gets down to almost empty, youll never run that pump dry for 30-60-1000 miles btween fill ups either

thats what i think i would do ...
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Old 01-04-2006, 10:09 PM
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Why not use the tanks and pump from an efi truck that already has dual tanks? probabally be the easiest route.

I remember on my 88 F-250 the fuel pump was under the drivers feet in the frame rail and somewhere along the line it switched between the two tanks. Seems it would be pretty easy to adapt something like this especially if your already wiring the efi in. You could probabally find an old 88+ chevy to grab the parts from at any wrecker and the tanks should be on opposite sides like yours too.
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Old 01-05-2006, 03:01 AM
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Doc here,

Why not try what Aircraft manufactures do...

On main tank, and a Transfer jack (Fuel pump) that picks the fuel from the satellite tank (s) and pumps it into the main tank to always keep it full..

You'd need a level cut off that works with the main tank fuel sender..but I bet it would work..

Another approach could be what they do on a small private aircraft that are EFI.....Duel tanks, a left,right off selector and single system electrical for each..just do research on how they do it and maintain pressure during the switch..(I betting the pump outruns the system on GPH and just fills the void, so no caveatting is detected)

Anyway try a goggle search for Aircraft fuel systems..see what you find!

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Old 01-05-2006, 03:07 AM
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You can buy the correct valves. I have not looked for a good one, but I found a chepo one in a few seconds. Don't go cheap!, but jc whitney has them.


For fuel-injected systems operating up to 65 psi. Designed to prevent returning fuel to incorrect tank. Weatherproof fiberglass-reinforced nylon valve body. Valve grounds to frame. Meets or exceeds DOT standards. Fits 3/8" I.D. fuel hose. Recommended fuse: 10 amps. Can be wired so original dash gauge indicates fuel level in either tank. Includes: switch, faceplate, wiring connector, instructions. Hoses not included—order separately. 6-port valve required on vehicles with 3 lines attached to fuel pump. For 12-volt systems.

Motor-driven 3-port Electric Fuel Tank Selector Valve Kit ZX812687U $87.99

Motor-driven 6-port Electric Fuel Tank Selector Valve Kit ZX812705U $53.99

Hope this helps,
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Old 01-05-2006, 03:28 AM
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Thanks guys for the good ideas. There's definately a lot of different ways to do this. Some more complicated than others.
I like that valve posted by Brian_B. That could probably work pretty well. I could wire up two basically independent systems with the pumps in the tanks. The pumps would feed through the stock switch to the engine. Then I could use the aftermarket switch on the return line. Or I guess I could just use two aftermarket switches. One going to and one coming back from the engine. I don't think I'd mind having two switches to change tanks.
I've definitely gotta make a run out to a wrecker sometime soon and try to find a truck with stock efi and dual tanks. If I could get an all inclusive switch off a wreck that would be nice.
This project is on the slow track, but I appreciate the responses and I'll post back when I figure more out.
81 Grand Prix, 355, 700r4, 8.5" 4.10
64 Oldsmobile Jetstar, all original
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Old 01-08-2006, 11:07 AM
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Why not just tie the tanks together with a decent sized hose.

They will both keep the same level and will not matter which has the pump and which has the return.

Or just put the pump in the line that ties them together.
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Old 01-08-2006, 05:09 PM
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Most dual tank set ups use an electric pump in each tank and a check valve that prevents cross feeding. Most in-tank pumps are low pressure delivery pumps (such as Ford) that feeds into a high pressure frame mounted pump. Or you can use high pressure pumps in each tank and skip the frame pump...

All you need is one toggle switch to switch power to the left/right tanks and the ignition key. Very simple and easy to install.


Using a dp/dt switch the gauge can be switched simultaneously or you can use 2 fuel gauges (you already have a dual set up). A Chevy factory fuel pump switch will work. AutoZone sells them.

Of course, use common relays to power the pumps. You can't run 3 pump's current throught the ignition switch.

The return line can be just t'd to split the return to each tank to prevent overfilling.

Snooping around, info is split 50/50 as to whether the late model in-tank pumps will directly fit your existing tanks.

Last edited by xntrik; 01-08-2006 at 06:45 PM.
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Old 01-09-2006, 07:44 PM
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Linking the tanks with a simple hose would be the simplist, but I don't think it would work too well for this application. This is a 4x4 and I'll be in very remote areas. If something snagged and ripped out the hose I'd lose both tanks of gas and be stuck in the middle of nowhere as the wolves circle and the grizzlies charge.

A simple twin setup would be ideal because having a backup system if one failed would really be nice. I think I'm going to put a high pressure pump in each tank. And of course wire the relays to power one at a time through the stock switch in the cab. The truck has one fuel guage that switches through the same tank selection switch. I plan on keeping that setup.

I've been assuming that I'll find a stock type in tank pump, pickup, and float that'll fit the tanks I have now. I guess I need to look into that too. At some point I'll go to the wrecker and start looking for parts that'll fit.
thanks again for the replies,
81 Grand Prix, 355, 700r4, 8.5" 4.10
64 Oldsmobile Jetstar, all original
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Old 01-13-2006, 07:40 PM
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Check out an '87 or later 3/4 or 1 ton with dual tanks and TBI. I had an 87 3500 with TBI but it didn't have dual tanks.
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