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EFI/external pump/dual tanks/single return??

OX1

Bronco Guru
Joined
Aug 26, 2003
Messages
3,455
Have this 5.0 EFI sitting around and also have an exhaust backfire, only when warm, on my 70. Have not messed with ign too much, so it is possible it could be ign related, but I suspect it may be a sticking valve.

I think the dual tanks are cool and do not want to go to a single large rear tank. Was thinking of a rail mounted pump and a single return line to the main tank with a line between the tanks to equalize them. Obviously that would kind of be making just one big tank out them, but it would eliminate switching of pickups/guages as you could just use the main one and save the cost of a large tank.

I figure the main pump is returning just a slight amount less than it is drawing, so the gradual reduction in the main tank should be able to be kept up with by the cross over line from the aux tank.

And yes, this may not work at extreme angles (if gas bleeds back to aux tank), but this will be a street rig with possibly a very mild mud run or cruise through flat trails in the woods.
 

surfer-b

Contributor
Bronco Guru
Joined
Sep 7, 2006
Messages
2,971
I'm not sure I follow you on this but if this is the idea you have; HP pump drawing from the main mounted on the frame rail and just a line between the aux and main tank with no pump, I don't see how you will get fuel from the aux to the main, it would be like trying to sighon fuel out of a tank but not having the hose submerged in the fuel, all you would do is draw air into the line.
I used the front/rear setup, however I used the fuel selector valve then placed a pump downstream from that, this way when the main gets low I turn the fuel selector valve and turn on the pump, pumping fuel from the aux to the main, this setup works good, however the tanks MUST be vented from my experience anyway, others on here have said there tanks are not vented and have had no problems. I vented my tanks back to the charcoal canister as stock but eliminated the plastic bottle behind the drivers seat.
The return line is to the main tank. I also have the stock mustang intank pump.
 

73stallion

Bronco Guru
Joined
Mar 5, 2004
Messages
16,786
Loc.
Eugene, OR
do you plan on running an accumilator? just run your return line back the accumilator and stop it there. i've done it a few times and it works just fine.
 
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OX1

Bronco Guru
Joined
Aug 26, 2003
Messages
3,455
I'm not sure I follow you on this but if this is the idea you have; HP pump drawing from the main mounted on the frame rail and just a line between the aux and main tank with no pump, I don't see how you will get fuel from the aux to the main, it would be like trying to sighon fuel out of a tank but not having the hose submerged in the fuel, all you would do is draw air into the line.
I used the front/rear setup, however I used the fuel selector valve then placed a pump downstream from that, this way when the main gets low I turn the fuel selector valve and turn on the pump, pumping fuel from the aux to the main, this setup works good, however the tanks MUST be vented from my experience anyway, others on here have said there tanks are not vented and have had no problems. I vented my tanks back to the charcoal canister as stock but eliminated the plastic bottle behind the drivers seat.
The return line is to the main tank. I also have the stock mustang intank pump.

My thinking was a line between the bottom of both tanks that will force them to equalize when parked on level ground (or any time you are mostly level and not accel/braking/cornering). Could even use a check valve so the fuel will never go back to the aux.

I would only be using one HP pump, hopefully self priming and one return line to the main tank. I would vent one or both tank as needed.

The selector valve and switch for both in tank guages would be eliminated, only using the guage from the main tank.

I think I remember reading about a factory vehicle that had this setup. 2 tanks, one on either side of drivetrain and connected via a line/tube of some sort.

Last resort could be a low pressure pump that just transfers fuel from aux to main when you see main getting low. That may even be even easier as I could plumb it right into return line going to main tank anyway, although probably only when not running as that could cause temporary low pressure in the return line.
 
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OX1

Bronco Guru
Joined
Aug 26, 2003
Messages
3,455
do you plan on running an accumilator? just run your return line back the accumilator and stop it there. i've done it a few times and it works just fine.

I had not planned on it, but that could work also (keeping fuel system as is upstream I assume??). Any recommendations on one that works well??
 

needabronco

Bronco Guru
Joined
Jul 2, 2004
Messages
6,411
Loc.
Prescott/Farmington
Run a transfer pump from the aux. tank to the main tank. And plumb the efi return to the main. You could run a 'Y' and plumb the return and the transfer line into the filler neck, which would probably be the easiest route. Or find a 6 port dual tank switch.
 

surfer-b

Contributor
Bronco Guru
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Sep 7, 2006
Messages
2,971
I think it would be easier to run the pump between the tanks, adapting another port in the bottom of the aux. plastic tank might be asking for problems.
 

scsm76

Bronco Guru
Joined
Oct 6, 2005
Messages
1,433
Loc.
Shaver Lake, CA
I had a service truck once that was plumbed with a 3/8" line and pump from the transfer tank in the bed to the main tank so we could refill at the flip of a switch. Funny thing was the main tank would siphon diesel out of the the transfer tank so the main tank would never go below full until the transfer tank was empty. We had to install a valve in order to keep fuel in the transfer tank when we needed it for fueling equipment.
 

73azbronco

Contributor
Bronco Guru
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Nov 11, 2007
Messages
7,790
I'm with surfer, plumb everything EFI off the main, then run an electric pump line to the main from the aux, you can even use the efi return line if you put in a check valve to the aux so it doesnt get filled. Turn on the aux elec pump to run the aux fuel over to the main. Don't spend the time and trouble trying to double plumb a two tank EFI system.
 

surfer-b

Contributor
Bronco Guru
Joined
Sep 7, 2006
Messages
2,971
You don't have to adapt the tank. Install a port in the filler neck, or add a port into the sender

My thinking was a line between the bottom of both tanks that will force them to equalize when parked on level ground (or any time you are mostly level and not accel/braking/cornering).

In order for the tanks to equalize without a pump there will have to be a line in the bottom of both tanks, it will also have to be lower than the lowest point of each tank, at least lower than the aux. or close to it in order for all of the fuel to reach the main. The main tank will have to be vented or pressure from the return will cause fuel to be pumped back into the aux. Even with the tank vented unless a check valve is placed in the line between the tanks it may still cause fuel to flow to the aux.
The check valve would have to be something like a flapper valve that is in a live-well in a boat.
 
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OX1

Bronco Guru
Joined
Aug 26, 2003
Messages
3,455
I'm with surfer, plumb everything EFI off the main, then run an electric pump line to the main from the aux, you can even use the efi return line if you put in a check valve to the aux so it doesnt get filled. Turn on the aux elec pump to run the aux fuel over to the main. Don't spend the time and trouble trying to double plumb a two tank EFI system.

I'm sure that is what I will do when I get to putting this EFI motor in. I already have a left over self priming low pressure pump from my projection days, so I don't even have to do anything special to the aux tank.

Just have to figure the best way to fill the main tank. May be worth adding 2 returns since I have to add one for the EFI return anyway.

What is everyone doing to vent these older non-vented tanks??
 

eb66to77

Bronc'Ownly
Joined
Mar 26, 2005
Messages
2,558
Loc.
NOVA
I think you are adding another step to the process with pumping between tanks. The accumulator will help you in a few different ways including resolving the lack of baffles in the stock tanks and providing a point for the return line. Adding a return port to a stock sending unit is brainless and takes a couple minutes to do. I sweat mine in the rear tank and the front was already setup to do it from Duff.
 
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