Dual function reservoir delete
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Elder User
Joined: Apr 2015
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From: Boston, KY
Dual function reservoir delete
I am in the process of getting both fuel tanks operational. Front tank has a new in-tank pump and wiring connector so I actually have a functioning fuel gauge. I am getting ready to order a rear tank and install it, but wondering how I should go about running both tanks. My switch works and all stock wiring is good. I've read a lot of people don't like the dual function reservoirs, which is where my question comes in. If I choose not to use a DFR, do I need to have a 6-port electronic switched selector valve? Can I go with a 3 port and still somehow run return lines? I have a return style pressure regulator under the hood. Just trying to figure out the most efficient way to put this all together since I'm starting from scratch and have the chance to do it right.
Fleet Mechanic
Joined: Mar 2014
Posts: 1,926
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From: Saskatchewan Canada
You are correct in needing a 6 port valve. Possibly, you could consider two 3 port valves, but the operation in terms of flow pattern would be the same.
I understand the potential problems with the DFR, but I can honestly say that over the course of several trucks equipped with this system, I have never experienced a failure.
I understand the potential problems with the DFR, but I can honestly say that over the course of several trucks equipped with this system, I have never experienced a failure.
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Elder User
Joined: Apr 2015
Posts: 613
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From: Boston, KY
To add a slight complication to the situation, when switching out the fuel senders, I ordered ones with the fuel pump, hoping to use in-tank pumps in conjunction with the rail pump. Since the DFR is pressure activated, what pressure ranges does it need?
I would go with the electronic 6-port, but I am concerned about the fact that it needs a 5-wire harness to operate. I like the fact that the 3 ports only need a power line to switch.
I would go with the electronic 6-port, but I am concerned about the fact that it needs a 5-wire harness to operate. I like the fact that the 3 ports only need a power line to switch.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
The older style fuel system has a low pressure pressure in each tank. The DFR is in the low pressure side of the circuit. I believe the working pressure is in the 5-7 PSI range.
If you have high pressure pumps the factory DFR may not work.
If you have high pressure pumps the factory DFR may not work.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
The Ford manual states do not use more than 5psi air pressure when testing the DFR.
The in-tank pumps put out between 8 & 12psi for the 1989 and older trucks.
The 1990 and newer OBS trucks will put out 95-100psi into a closed head.
The 1987 an older E350 460 class "C" rv with dual tanks use an electric switching valve.
The in-tank pumps put out between 8 & 12psi for the 1989 and older trucks.
The 1990 and newer OBS trucks will put out 95-100psi into a closed head.
The 1987 an older E350 460 class "C" rv with dual tanks use an electric switching valve.
Hotshot
Joined: Jun 2015
Posts: 12,877
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The dual function reservoir in my '89 was stuck from the truck sitting for about 9 years. It only allowed access to the front tank which I found out on the highway the first time I went to switch tanks after getting the truck back on the road. I got one from the junkyard to replace it and have not had anoher problem in the last 40K miles.
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
What exactly are you working on here? Are you fixing up an older(pre '90) truck or is this a complete custom job?
The best way to eliminate the DFR is to simply use a '90+ tank and pump, then the fuel lines simply go straight to the engine and back and if 2 tanks are used there is nothing additional needed besides the dash switch.
The best way to eliminate the DFR is to simply use a '90+ tank and pump, then the fuel lines simply go straight to the engine and back and if 2 tanks are used there is nothing additional needed besides the dash switch.
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Elder User
Joined: Apr 2015
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From: Boston, KY
Consider it complete custom. All I started with was a midship tank and a frame mounted pump. In-tank pump was not there. With a '90+ tank and pump, how does the return go back to the right tank?
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FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
With the '90+ system the FDM inside each tank has check valves that only open when that unit is active, this prevents backflow through the high pressure line as well as return crossflow to the wrong tank.
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