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I'm planning on plumbing in a return line for 84 f150 (351w) and and I'm hoping to use mostly oe parts. i know there's a selector valve that can do both the return and the feed. I'm just uncertain what i need to do for wiring. And I'm wondering if there's sending units available that'll give me return fittings or if I'll have to drill the tanks. I'm going to run an external fuel pump on the frame rail so the sending units with allocations for a fuel pump are not ideal. Unless both barbs are 3/8 and i can just swap the lines.
Looking into the wiring further, it looks as if i would need a different selector switch. Which doesn't appear to be sold and the aftermarket switch that comes with some of the 6 pin valve kits is less then ideal from a cosmetic standpoint. I could just run 2 of the stock 1 wire valves i guess
Got to ask why do you want to mess with the fuel system by adding a return and electric fuel pump?
You know you should wire the pump with a relay and safety switch so when the motor is not running the pump is not running like in a crash.
Being you have a tank switching valve I am guessing you have dual tanks also?
I think if we know why you want to do this we might have a better way to make it happen.
Dave ----
Got to ask why do you want to mess with the fuel system by adding a return and electric fuel pump?
You know you should wire the pump with a relay and safety switch so when the motor is not running the pump is not running like in a crash.
Being you have a tank switching valve I am guessing you have dual tanks also?
I think if we know why you want to do this we might have a better way to make it happen.
Dave ----
I'm already running an electric pump. I put in a 351 out of an efi truck so I didn't have the parts necessary to run an mechanical. And i also didn't want to have to run the starter to prime fuel since i don't constantly drive my truck. Yes it's dual tanks and yea i know i need a safety for the fuel pump i have a plan for that. As for the return, it gets very hot here in the summer so I'm trying to remove any opportunity for the fuel to vaporize. And the return system will keep fuel cooler which will improve reliability and performance as well take load off of the pump
Last edited by triorez25; Apr 1, 2026 at 02:37 PM.
For electric impeller type pumps it may be counterintuitive, but when they are running free they are turning more and using more power than you think. When pushing against some pressure it can slow down the motor making less load on the system. That in and of itself might not be a reason to add a return. What kind of electric pump are you using?
A good reason to have a return is to prevent vapor lock, but then a midship low on the frame epump is good insurance for that.
If your pump produces more pressure and volume than needed a return could aleviate a flooding issue by overwhelming a carb designed for 4 to 6 psi.
I'm already running an electric pump. I put in a 351 out of an efi truck so I didn't have the parts necessary to run an mechanical.
Is the engine still EFI, including all of the electronics, etc.? Or did you swap over the intake and carb from the pre-EFI engine and now there's no provision for a mechanical pump?
Reading between the lines, I think you mean the latter but want to be sure.
Originally Posted by triorez25
And i also didn't want to have to run the starter to prime fuel since i don't constantly drive my truck.
As for the return, it gets very hot here in the summer so I'm trying to remove any opportunity for the fuel to vaporize.
I work my 351W truck VERY hard in the summer, hauling a slide-in camper in hot weather. I had LOTS of problems with heat affecting the fuel, as detailed at the link above. I converted to full electric, with no return line, and kept the stock 3-port fuel switching problem. Zero problems since then.
The only other major modification I made was to block off the exhaust crossover passage in the stock intake manifold.
For dealing with heat affecting the fuel, aka "Vapor Lock", keep in mind there are two aspects to the problem. For best results, you'll want to address both issues. Lots of good details in this thread:
OE parts will be copying a 460 fuel system which does use in tank pumps.
If you do not mind putting a return line in the tank itself, that would be the way to go. If you want a safer way to put a return line in place on both tanks, you could take the metal filler neck off and modify it on the bench to accept a fuel fitting and let the return fuel run down the filler neck hole.
For the return part of it at the carb, I would run one of these aftermarket fuel filters that has 3 ports. Chryslers used these alot.
As far as the valve, you just need a 6 port that came on the 460 trucks and the diesel trucks. You are correct this valve had special wiring. Several ways to go about it. First off, the valve you need is a 6 port Pollack valve, that is the company that makes them. You can buy these valves in the store with a switch that comes with it.
If you wanted, you could mount the valve and plumb it in, and run two new wires to the new switch you mount somewhere. This switch will need a power and a ground wire running to it, and then the two wires to the valve. You could leave your original switch, but you would need to flip both to change tanks.
Here is what the valve and the switch looks like. If you do any research, you will see this valve has more than two wires going to it. That is because this valve also switches the sending unit wiring. But if you keep your original dash switch, you will not need to use this feature and you will only need two wires to the valve.
Dave F, lot's of good info in your last two post. Is it possible for you to come up with a "How Too" for doing this ?
I see post on here now and then, asking about the 6 port switch. Would this also work to replace the OEM switching on our years ?
As far as the valve, you just need a 6 port that came on the 460 trucks and the diesel trucks. You are correct this valve had special wiring...
What if you simply kept the existing 3-port valve for the fuel supply and added a second valve for the return? You wouldn't have to change any of the wiring for the gauge. The only wiring mod would be to add the second valve in parallel with the first one.
What if you simply kept the existing 3-port valve for the fuel supply and added a second valve for the return? You wouldn't have to change any of the wiring for the gauge. The only wiring mod would be to add the second valve in parallel with the first one.
You could but have you thought out the fail safe operation? What happens when the return valve fails to behave?
If you have dual tanks and return lines the best choice is the 6 port valve designed for that. My experience with the 6 port when stuck between tanks the return lines behaved similarly and no plugged return or overflowing tanks. I assume they open and close together as a mechanically operated valve. No worry about electrical failure screwing up the valve coordination.
What if you simply kept the existing 3-port valve for the fuel supply and added a second valve for the return? You wouldn't have to change any of the wiring for the gauge. The only wiring mod would be to add the second valve in parallel with the first one.
You could. You do not have to change the wiring for the gauge with the 6 port valve if you do not mind having two switches to change the tanks. But your idea of two 3 port valves would work. 2x3=6 ports.
I been running my 3 port valve for six years now and the only failure I had was I shorted out the feed wire and blew the fuse. In that case both valves would have failed at the same time.
I would go with the 2nd 3 port as it is stupid simple to setup.
I also have not heard of a 3 port failing when being used like the 6 ports. Any 3 port you hear not working is from someone that just bought the truck and dont know the last time it has worked.
Kind of like when I first got my truck as the 3 port did not work and dont know when it stopped before I bought the truck.
Dave ----
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