Solenoid to Motorized Fuel Tank Selector Valve

[Dukagora]

79 C20 454 Crew Cab.

I am trying to figure out the wiring. How this all works. I have read a lot and thought I got it only to realize several times that something else I read confused me. I know the system is simple, but still not getting it.

I have a switch I thought I needed - part # S9002(works on O'reilly website for sure). I have read that if the switch says "push to fully depress", its for a solenoid valve. If not it will work with the motorized valve. Is this correct? If not correct....

Valve is the 6 port that used the 5 pin connector with A-E having pins in it.

I had expected to have to use the switch in the link to make things work.
https://www.homedepot.com/p/Gardner-...W-16/100210997

https://www.youtube.com/watch?v=-E9NwIn6_sk
If you skip to 8:42 of this video, is the wiring correct on this switch? Also, are the instructions provided in this video accurate? I assume so but just don't have the experience/knowledge to be sure.

If the video in the link is accurate, how do you get the signal from the sending units for gauge levels? I have attached photos of what I currently have. Do I need to cut the blue wire off the factory connector and stick it to the corresponding, apologies for incorrect terminology, terminal on the switch? Same for pink wire from passenger? "Middle terminals".

I have a pink wire coming off of the passenger side tank.
I have a blue wire coming off the drivers side tank.

The Switch was working correctly as there was gas in the drivers tank when I dropped from the truck.

Attached pics are probably obvious for most of you, but, the one in hand is to the switch at the dash. The other is inside cab at firewall.

Sorry I know there are a lot of threads out there and Hatzie for an example, has been pretty thorough.

[Dukagora]

Wire for power I believe.

[hatzie]

S9002 is the BWD switch for the 1979 and prior solenoid valve system. This switch will not work on the motorized valve without a bunch of work building a pair of relays into the circuit.


DEPRESS FULLY is emblazoned on the momentary switch GM used for the motorized valve from 1981-1986. It's not for the 1980 & prior solenoid valve system. There are several negatives associated with that switch and the motorized valve. If you aren't doing a concourse restoration on a 1981-1986 truck then don't use one of these with the motorized valve.



I recommend the plain face ON-ON switch GM used on the 1987 TBI R1500-R3500 & V1500-V3500 squarebody trucks for 1981 and later installs and retrofits of older solenoid valve equipped trucks. Standard Motor Products D-1807 or AC Delco D7089C.


You're looking at how to replace the 1980 and prior solenoid system with the 1981 and newer motorized valve system...

Has your old 6 port solenoid valve failed?
Are you sure it's not a failed dash switch?

[Dukagora]

Thing is there isnt a valve at all. Was bypassed and removed long ago it appears. I wasnt able to find the solenoid version with the single wire through any parts vendors I am familiar with.

[hatzie]

Originally Posted by Dukagora

Thing is there isn't a valve at all. Was bypassed and removed long ago it appears. I wasn't able to find the solenoid version with the single wire through any parts vendors I am familiar with.

That valve is long long long obsolete. You may be able to find a dubious pedigree unit on evilbay for an astronomical price.

I wouldn't bother.

The intention for my writeup in the Dual Tanks Theory of Operation thread was to demystify how the motorized valve works...

Industry standard LH & RH... Are the seated drivers Left and Right hands on the wheel while driving. It avoids confusion to use LH & RH in this manner. I work on Brit cars. The Brits put the passengers on the wrong side.

How to swap over...

The easy way is to find a 1981-1986 gasoline or a 1981-1991 diesel NL2 sub-harness and plug it into your truck at the gauge disconnect on the RH frame rail and power/ground connections in the cab.

Or... Harnessworx makes a brand new dual tank harness for the GM carbureted and diesel trucks. He also builds custom dual tank harnesses for TBI and LS EFI swaps as well. The proprietor goes by the handle Gmachinz on this and several other boards.

You can roll your own harness. I would make a completely new harness in a heartbeat but I have the skills, tooling, and various parts in my barn.

The AC Delco D7809C rocker switch used a now obsolete keyed female Packard 56 plug. A 2977048 four position unsealed unkeyed Packard 56 plug will work on the stock AC Delco D7089C switch but keep in mind it's not keyed to the switch so you can plug it in upside down.

If you are familiar with terminating Weatherpak terminals and have the correct tooling to do a good job... get a handful of the 12124580 16-14ga female tower terminals and the 15324982 green wire seals along with one 12015799 six position female tower plug and one 12010300 cavity seal for the F cavity.
Pollack and Delco sell a repair pigtail with the six position tower connector and five wires with the same color jacket. You can solder and heatshrink one of these in place if you don't have the skill set to terminate your own plug.


If you're rolling your own harness. Remove the existing NL2 harness completely.
You'll want to liberate the Pink, Pink/White, and Light blue wires from the old harness.
The Pink/White and Light blue wires have molded plugs for the senders. These wires will need to be routed to Terminals A & C on the valve plug. A is usually the RH tank and C is usually the LH tank. This is completely dependent on the polarity you choose for D & E on the valve.

The solid Pink wire has the NL2 harness side molded disconnect plug that connects the gauge to the senders through the dash switch on you 1979. You'll need to route this wire to terminal B on the Weatherpak plug.

The Pink wire with the Black tracer that runs to the 1979 dash switch is the original system power.
The 1979 system does not have a ground to the switch but the 1981 and later system does. I usually cabbage one of the 1983 & later plug in buss bars that attach to the kick panel right above the E-Brake. It makes adding grounds in the dash painless and clean.

You will need a firewall grommet and two wires to run from the switch to D & E on the valve. I believe stock 81-86 was Green and Gray. GM used a male and female Weatherpak at the firewall disconnect on some years. One of those will make it easier to install inside the cab.

I usually protect any wiring I modify or install with expanding mesh sleeve and split poly loom.

I also usually draw any wiring mods beforehand with lots of notes to make sure I know exactly what I need to do. If you want a DXF file of the valve and switch guts to draw your own out in CAD I have em.

[Dukagora]

I think most of you are mechanics. Sadly I am not at all. I have some experience working on vehicles. Had a 77 that needed an engine rebuilt but once the failed cam was identified, my stepdad and I opted to have a machine shop rebuild it and we dropped it in. He handled the timing.... I pulled the engine on my wife's car and had it rebuilt after it dropped an intake valve seat. Had some help getting the engine in just because it was very stubborn lining up, but it was mostly a plug and play thing I think. Everything laid back in to position for me wiring and hose wise.

I don't have the skill set for soldering, or making my own connectors. I also don't have CAD and if I did, I don't know anything about that either. So I think that leaves me to doing my own wiring harness.

I think there are still some questions left for me.

I attached 2 pictures. One is the toggle switch from the video I saw. I assume this wiring is right. If so, how do I attach the 2 wires that will feed pins D and E on the weatherpak? The other picture is what I believe to be the green wire that originally fed the solenoid valve. This would have power on it that gets transfered to it FROM the original switch connector and would originally get that power from the pink wire with black tracer right? Also, this Pink wire with black tracer appears to go only to the old connector switch. It does not feed power to anything else right?

https://www.online-led-store.com/2-w...orzacclbrxxxa6
I need what is in the link right? I’m using that for reference in the paragraph below.
The pink wire with black tracer will need to be removed from the old connector and routed to this weather pack right? Or does it go to the toggle switch as power to the toggle switch, which would then have 2 wires coming off of it to the 2 wire weather pack that goes to the fire wall, and out to D and E with those 2 wires being wired to maybe the bottom terminals on the toggle switch? You don’t mention removing pink with black tracer from the old connector in your response so I assume I am not understanding this portion of the process. The only wire left in the original switch connector would then be green.

How do I make sure I route RH to A and LH to B? I know this isn't critical as long as sending units for those tanks match but I like the sound of running it that way, especially if it’s typical.

Does any of that make sense? I did draw things out from the connector, but in doing so, I realized I am just not sure how the toggle switch side of this will work. Which wire should go where on the toggle switch etc. I am using the picture as my platform for how to wire the switch, with no understanding of how to get it all wired to that switch correctly. One side would be for LH and one side for RH with the two middle terminals likely being the power from or to the valve to switch its position for each tank.

And FINALLY, the video says to send power to the toggle switch directly from the battery with a 10 amp inline fuse. IF I can use the pink wire with black tracer for power to the toggle switch like I thought I could, it runs into the, sorry if the terminology is wrong, bulkhead connector and should already have a fuse, so do I still need to do the inline fuse and power from the battery directly?

Ok one more thing. Gauge wire size. I bought way too much wiring in 16 gauge for this project. Should I be too worried if I cant get the same gauge 2 wire weather pack from a local store? So say they have 12 or 14 gauge but nothing smaller. Is that an issue?

[hatzie]

Originally Posted by Dukagora

I think most of you are mechanics. Sadly I am not at all. I have some experience working on vehicles. Had a 77 that needed an engine rebuilt but once the failed cam was identified, my stepdad and I opted to have a machine shop rebuild it and we dropped it in. He handled the timing.... I pulled the engine on my wife's car and had it rebuilt after it dropped an intake valve seat. Had some help getting the engine in just because it was very stubborn lining up, but it was mostly a plug and play thing I think. Everything laid back in to position for me wiring and hose wise.

I don't have the skill set for soldering, or making my own connectors.

I'm not trying to be nasty just firmly in touch with reality. If you don't have the skills to solder in pigtails or build your own connectors you will not be making a wiring harness that will last. Butt splices and Scotchlok taps will corrode and fail within a year or two.

You can buy some tooling and learn. That's how I did it.

Harnessworx makes a brand new dual tank harness to retrofit the Pollack Motorized valve into the earlier trucks. It's ready to plug in with a new REAL Pollack valve, all of the grommets, obsolete connectors, and other pieces you need already assembled. Nice, clean, and easy. You can order them without the valve... inquire on the price without it.
If you have a China-made parts store valve I'd take it back and get the real McCoy made by Pollack that gmachinz includes with the harness.
Here is the thread where he offered them for sale...http://67-72chevytrucks.com/vboard/s...d.php?t=706027

Originally Posted by Dukagora

I also don't have CAD and if I did, I don't know anything about that either. So I think that leaves me to doing my own wiring harness.

The Kitchen table, a big sheet of paper, something close to a straight edge ruler, a couple #2 pencils or a bunch of colored pencils, and a big pink eraser (not for colored pencils) works too. I was just offering the DXF files if that would've been helpful...
The point of drawing it is to put what you are doing on paper so you can see it and see whether there are errors.
Something like this drawing I made of the stock motorized valve wiring with contrasting colors to illustrate wire functions.

You can shortcut drawing the whole thing... download and print this PDF of the above image and write on it with pencil...
Motorized Early REV B.pdf

Originally Posted by Dukagora

I think there are still some questions left for me.

I attached 2 pictures. One is the toggle switch from the video I saw. I assume this wiring is right. If so, how do I attach the 2 wires that will feed pins D and E on the weatherpak? The other picture is what I believe to be the green wire that originally fed the solenoid valve. This would have power on it that gets transfered to it FROM the original switch connector and would originally get that power from the pink wire with black tracer right? Also, this Pink wire with black tracer appears to go only to the old connector switch. It does not feed power to anything else right?


https://www.online-led-store.com/2-w...orzacclbrxxxa6
I need what is in the link right? I’m using that for reference in the paragraph below.
The pink wire with black tracer will need to be removed from the old connector and routed to this weather pack right? Or does it go to the toggle switch as power to the toggle switch, which would then have 2 wires coming off of it to the 2 wire weather pack that goes to the fire wall, and out to D and E with those 2 wires being wired to maybe the bottom terminals on the toggle switch? You don’t mention removing pink with black tracer from the old connector in your response so I assume I am not understanding this portion of the process. The only wire left in the original switch connector would then be green.

How do I make sure I route RH to A and LH to B? I know this isn't critical as long as sending units for those tanks match but I like the sound of running it that way, especially if it’s typical.

Does any of that make sense? I did draw things out from the connector, but in doing so, I realized I am just not sure how the toggle switch side of this will work. Which wire should go where on the toggle switch etc. I am using the picture as my platform for how to wire the switch, with no understanding of how to get it all wired to that switch correctly. One side would be for LH and one side for RH with the two middle terminals likely being the power from or to the valve to switch its position for each tank.

And FINALLY, the video says to send power to the toggle switch directly from the battery with a 10 amp inline fuse. IF I can use the pink wire with black tracer for power to the toggle switch like I thought I could, it runs into the, sorry if the terminology is wrong, bulkhead connector and should already have a fuse, so do I still need to do the inline fuse and power from the battery directly?

Ok one more thing. Gauge wire size. I bought way too much wiring in 16 gauge for this project. Should I be too worried if I cant get the same gauge 2 wire weather pack from a local store? So say they have 12 or 14 gauge but nothing smaller. Is that an issue?

I wouldn't use a toggle switch if your truck had the dual tanks originally. Just get the $13 Delco D7809C switch and massage the rectangular hole to fit it. If you're building your own harness it's much easier to work with too.



As long as your pigtails are not smaller gauge wire than the harness wires you can safely use them. The smaller number gauges are larger wires... 12ga is larger than 14ga or 16ga. It doesn't look as clean and neat as connector terminated wires or the same gauge pigtails but they can be used.

[akart]

Originally Posted by hatzie

S9002 is the BWD switch for the 1979 and prior solenoid valve system. This switch will not work on the motorized valve without a bunch of work building a pair of relays into the circuit.
Attachment 1781509

DEPRESS FULLY is emblazoned on the momentary switch GM used for the motorized valve from 1981-1986. It's not for the 1980 & prior solenoid valve system. There are several negatives associated with that switch and the motorized valve. If you aren't doing a concourse restoration on a 1981-1986 truck then don't use one of these with the motorized valve.

Attachment 1781517

I recommend the plain face ON-ON switch GM used on the 1987 TBI R1500-R3500 & V1500-V3500 squarebody trucks for 1981 and later installs and retrofits of older solenoid valve equipped trucks. Standard Motor Products D-1807 or AC Delco D7089C.
Attachment 1781520

You're looking at how to replace the 1980 and prior solenoid system with the 1981 and newer motorized valve system...

Has your old 6 port solenoid valve failed?
Are you sure it's not a failed dash switch?

I have an '86 C10 and am replacing the switch and solenoid unit.Had/have the (depress fully switch) Is the AC Delco D7089C a direct replacement ie; same wiring/plug in. Plug and play?? Something went wrong and only have the right tank so am replacing both units as they are old and maybe a shorted wire killed the solenoid. I am seeing a green wire that was shorted on the manifold.

[Dukagora]

No I am pretty sure it is not plug and play. I just got the switch myself and it only has 4 terminals on it for a blade type connection. I wish they would have shown that in the pictures of the item for sale so you can see it before you buy.

I think all I need to do currently is confirm which wire is for fuel sending unit in the back of my dash cluster connector, and I guess cut it and bypass where ever it goes and run it down to my new connector.

I had thought the wire was going to be located right behind the fuel gauge itself, just hanging there waiting to be conveniently used, but no such luck!


I snagged the wiring diagram for my year truck from Hatzie's incredibly convenient signature and think I figured out which one it is, just need to make it happen. That and wait for new fuel tank straps. I borrowed a strap with mount from a fuel tank oriented to the other side of the previous truck it belonged to. Turns out the fuel tank mounts are side specific too!

[hatzie]

Originally Posted by Dukagora

No I am pretty sure it is not plug and play. I just got the switch myself and it only has 4 terminals on it for a blade type connection. I wish they would have shown that in the pictures of the item for sale so you can see it before you buy.

I think all I need to do currently is confirm which wire is for fuel sending unit in the back of my dash cluster connector, and I guess cut it and bypass where ever it goes and run it down to my new connector.

I had thought the wire was going to be located right behind the fuel gauge itself, just hanging there waiting to be conveniently used, but no such luck!


I snagged the wiring diagram for my year truck from Hatzie's incredibly convenient signature and think I figured out which one it is, just need to make it happen. That and wait for new fuel tank straps. I borrowed a strap with mount from a fuel tank oriented to the other side of the previous truck it belonged to. Turns out the fuel tank mounts are side specific too!

Fuel tank mounts are not side specific. However. There's front and a back mount.

Trying to make the Solenoid harness run the motorized valve, as-is, is like trying to microwave with your toaster.
You can re-use the sender connectors at the tank and the wire with the gauge disconnect on the frame rail along with enough wire to reach the new valve connector. The rest will need to be fabbed.

The fuel-gauge wire disconnect is on the Right Hand frame rail near the valve. It's in the solid Pink wire.
This is a contrasting color diagram that shows wire and connector functions of the 1973-1980 solenoid system. Notice the wildly different switch connections and the fact that the fuel gauge wires run to the dash switch rather than the valve.
The task you have set for yourself is to change the below system to the one in post 13.
It's worth noting that the RH tank could be designated production or aux depending on the year and who monkeyed with it before you.



Solenoid_Generic.pdf

[Dukagora]

Fuel gauge disconnect wire?

The drivers side is blue and, I am not in front of the truck atm, but am pretty sure the blue one has the same set up. So they disconnect from the wires running to the cab and would go to the correct spots already listed on the fuel tank selector valve. The PINK wire with the electrical tape would then become the fuel gauge wire going to the new connector on the fuel tank selector? Is that remotely right?

[hatzie]

Originally Posted by akart

I have an '86 C10 and am replacing the switch and solenoid unit.Had/have the (depress fully switch) Is the AC Delco D7089C a direct replacement ie; same wiring/plug in. Plug and play?? Something went wrong and only have the right tank so am replacing both units as they are old and maybe a shorted wire killed the solenoid. I am seeing a green wire that was shorted on the manifold.

The OP wants to convert his 1975-1980 solenoid valve system to the 1981-1991 motorized valve system that you already have on your 1986 C10... If your dual tanks are factory installed you don't have a solenoid valve.

Here's the writeup I posted on how the motorized valve system works.
http://67-72chevytrucks.com/vboard/s...82&postcount=2

Shotgun repairs are generally expensive and frustrating. Before you throw an $80-150 valve at it replace the $13 switch and repair the damaged wires blown fuse etc... then test the system. Usually, the switch is the problem.

The 87-91 D7089C switch is a drop-in replacement for the 81-86 DEPRESS FULLY switch with the added bonus that it actually lasts. It will plug right in and snap into the dash where the original switch lived.

I'd start a new thread about your problem rather than highjack this one.

[Dukagora]

Maybe I should say if you want dual tanks, it appears that the motorized valve is your only option as far as I can tell

[kipps]

Originally Posted by Dukagora

Maybe I should say if you want dual tanks, it appears that the motorized valve is your only option as far as I can tell

For a traditional carb or tbi setup, yes.

For any setup, such as a LS swap, that uses a pump and regulator mounted in or near the tank, you can skip the selector valve altogether. Use a DPDT rocker switch in the dash, use one side for switching the fuel sender. Use the other side to switch the ECM signal between two fuel pump relays. Each side is completely stand-alone, including it's own relay, pump, regulator, return line, and check valve. The two check valves would feed into a common fuel line going to the fuel rail.

This system would be a lot more robust than any selector valve setup. The only single failure point would be the rocker switch. If any other part fails, you could run on the other side with no problems. If a check valve were to stick open, you could continue to run on that side, but not the other.

This would require a little more custom wiring. So if your truck has immaculate wiring already, you might want to stick with a selector valve.

[Dukagora]

So what are the negatives with the motorized switch?

Given there are no other options if you want to utilize dual tanks, how do you correctly wire a toggle switch in? Id rather not do it all that way but it looks like I don't have a choice.

So as it stands for me now, the switch can be wired as shown in the video I linked.

I need to get power to the valve.
I need to the sending units wired in so the gauge works for both.

Those, I assume 3, wires are found in the original harness.

However given the FSV3A valve connector is required for the motorized valve, I need to actually reroute the sending unit wires from each tank FROM the cab, to, I assume, A and C in the video diagram for the FSV3A valve connector. Leaving the original connections at the fuel tank sending units. Or do I leave those wires and use 1 wire from the harness to go to B on the FSV3A valve connector?

I have 1 wire I can provide for power to this valve based on the toggle switch wiring in the video....I think. How do I wire that 1 wire to D and E? The power is reversed when I switch it at the cabs toggle switch right? Does that make sense at all? I don't wire my power source from the toggle switch to BOTH D and E? Pretty sure that wont work.

[Dukagora]

Or maybe I could just follow Rich Weywands post on how to do this?

http://67-72chevytrucks.com/vboard/s...d.php?t=684116

Post #5.

Hatzie I got confused when you said there was a switch that would do the same as described in that post and still had the factory look. I had hoped to retain that but then learned about momentary switches which I think the links switches were. Either way I'm just gonna wire it the way I have seen and see what happens.

Thanks for the info everyone.

[wilkin250r]

You are correct. The old 6-port solenoid valve is nearly impossible to find. If you want dual tanks, the motorized valve is your only option.

[wilkin250r]

I can't walk you through the details, but the theory is really simple if you understand electronics.

The old solenoid system used one power wire, and two signal wires. Three wires running back to the tanks.

The motorized valve uses two power wires, and one signal wire. Still three wires, so you re-purpose one of the signal wires as a power wire, and route the wires accordingly.

[hatzie]

That rubber ball in your picture is the tank harness main fuel gauge wire disconnect. Hopefully that E-tape doesn't mean the wire is chewed beyond repair. I have used Weatherpak single terminal disconnects to repair chewed up fuel guage wires.
That's the clearest picture I've seen of that little monster. With your permission I'd like to add that picture to the theory of operation writeup.

If you don't like to solder I highly recommend investing in some very versatile Delphi and Ideal tooling.
Unsealed Terminal Ratcheting Crimping Tool Delphi # 12085271
Sealed Terminal Ratcheting Crimping Tool Delphi # 12085270
The Delphi crimp tools are around $90 each but you will not be disappointed in the quality and ease of use.

10ga-20ga Ideal Stripmaster can be had from Lowes for around $30. Again well made and versatile and well worth the money.

#00 flat blade screwdrivers can be used to extract Packard 56/59 terminals. Other connector families need specific extractors. You can find the Delphi Weatherpak extractors for around $6. Delphi extractors for Metripack and other connector families on our 40 year old trucks are around the same.

There are a couple reference textbooks in the manual thread that show the various connectors and how to insert/extract terminals from them... as well as how properly crimped terminals should look.

[Dukagora]

Ha! With as much help as you have given so far!? Please by all means use it!

If there is anything else that this truck might have that you need I will gladly search for it.

[hatzie]

Originally Posted by Dukagora

Ha! With as much help as you have given so far!? Please by all means use it!

If there is anything else that this truck might have that you need I will gladly search for it.

If the E-tape is covering a damaged wire jacket you can usually slide heat-shrink down over the damage to seal out the weather. I'd let it dry and wipe grease on the exposed wire to arrest any corrosion.

[Dukagora]

[QUOTE=hatzie;8257078]That rubber ball in your picture is the tank harness main fuel gauge wire disconnect. Hopefully that E-tape doesn't mean the wire is chewed beyond repair.

You assumed right! There were two sections of bare wire on that.....wire. "protected" by electrical tape. 2" and 1" sections. I had to cut back a bit before that to get some decent wire and it worked out.

[Dukagora]

Hatzie I have what I think is the final question for all of this. I had all wiring connected and verified that everything works as it should. Can hear the valve click over and everything etc. etc.

Once verified, I disconnected the battery again and had to tuck everything away to make sure there was no issues with wires hitting the exhaust etc. etc. After doing that hooked up the battery again to do one more test run and I lost all dash power. Truck started and ran fine, but no dash lights. I took out a test light, not sure what I was doing. With the test light grounded to the dash, I started touching the tops of fuses. The first one I touched was a 20 amp which I didn't know at the time, but it was for the dash. Right side lit up but left didn't. Not sure if that was normal or not but figuring it wasn't, I started checking other fuses. Both sides light up on every fuse but that one.

After 10 minutes of cursing my luck at not having a 20 amp fuse, I found one! Confirmed I have enough 10 amps to replace them all in every squarebody in the country! At any rate, plugged in the new fuse and everything works again.

Obviously now the concern is what caused the blown fuse. To power the switch, I used the ignition wire that powered the original switch. I did NOT use any inline fuses of any kind. Just removed the wire from the old switch and moved it to the new one. Is this the reason the fuse blew? I realize that's not easy to verify, but there sure seems to be a connection to me. Any suggestions you might have for voltage checks would be much appreciated.

[Dukagora]

I guess I now have another question! Initially I wasn’t going to ask but it’s started eating at me as it doesn’t make sense.

I was under the assumption that on a fuel sending unit with 3 ports the hoses were as follows and performed the following roles:
3/8 = Fuel TO the carb/engine.
5/16 = RETURNING raw fuel that was NOT used by the engine.
1/4 = Fuel....vent? Vapor?

When I did my initial testing to make sure everything worked, I never hooked up the ¼” line because I thought vapors would be the only thing coming out of those ¼” hoses. Not fuel. So both drivers and passenger were not hooked up. When I replaced all the hose, I did it one size at a time where there was hose, so I wouldn’t, in theory, goof things up. Either way, after I got to this point I started the truck. Checked for leaks. Found a pool of it under the truck and figured I forgot to tighten a hose clamp. However it was coming out of the ¼” line. Dripping after I shut the truck off for a lot longer than I would have expected it to. No fuel from anywhere else. Passenger side only. The same line I thought was for fuel vapor and NOT fuel. This doesn’t make sense though because why would you route fuel vapor to a tank selector valve if that isn’t what the 5/16” does?

What this, to me, translates to currently is that the only return line for fuel is that ¼ inch? So that means as I’m driving on the drivers tank, all fuel that gets returned is actually going to the passengers tank. And if the passenger tank is full…….eventually it will overfill and find a way out of the tank? Either way something must not be hooked up correctly.

Or am I wrong on which port fills each role? Maybe when the tank was bypassed years ago this is how it was done? For one tank it probably wouldn’t matter? I saw a picture somewhere while researching this, and finding the info for me at least wasn’t easy, but the picture showed only the 5/16” port labeled and said it went to the canister. Then I found another thread that lists it the way I have. This list makes sense with the fuel tank selector valve, or my understanding of it. This all lines up with hatzies Dual Tanks Theory of Operation thread. So maybe there was an issue and what I am seeing is the PO bypassing an existing issue to get fuel to return to the tank?
I assumed fuel doesn’t go into a plastic canister filter and then back out but I might be wrong?

Someone show me the light please!!

I am certainly getting under the truck yet again tonight but wanted to make 100% sure I am correct on what I think I know before I tinker with it.

As always thanks for the help!

Edit: guess I am an idiot because it cant be plumbed any other way than 1/4" off the mechanical. So I wont be messing with anything. Still don't quite understand how 5/16" is the return line when it runs from the passenger tank to the canister though.

[hatzie]

Originally Posted by Dukagora

I guess I now have another question! Initially I wasn’t going to ask but it’s started eating at me as it doesn’t make sense.

I was under the assumption that on a fuel sending unit with 3 ports the hoses were as follows and performed the following roles:
3/8 = Fuel TO the carb/engine.
5/16 = RETURNING raw fuel that was NOT used by the engine.
1/4 = Fuel....vent? Vapor?

When I did my initial testing to make sure everything worked, I never hooked up the ¼” line because I thought vapors would be the only thing coming out of those ¼” hoses. Not fuel. So both drivers and passenger were not hooked up. When I replaced all the hose, I did it one size at a time where there was hose, so I wouldn’t, in theory, goof things up. Either way, after I got to this point I started the truck. Checked for leaks. Found a pool of it under the truck and figured I forgot to tighten a hose clamp. However it was coming out of the ¼” line. Dripping after I shut the truck off for a lot longer than I would have expected it to. No fuel from anywhere else. Passenger side only. The same line I thought was for fuel vapor and NOT fuel. This doesn’t make sense though because why would you route fuel vapor to a tank selector valve if that isn’t what the 5/16” does?

What this, to me, translates to currently is that the only return line for fuel is that ¼ inch? So that means as I’m driving on the drivers tank, all fuel that gets returned is actually going to the passengers tank. And if the passenger tank is full…….eventually it will overfill and find a way out of the tank? Either way something must not be hooked up correctly.

Or am I wrong on which port fills each role? Maybe when the tank was bypassed years ago this is how it was done? For one tank it probably wouldn’t matter? I saw a picture somewhere while researching this, and finding the info for me at least wasn’t easy, but the picture showed only the 5/16” port labeled and said it went to the canister. Then I found another thread that lists it the way I have. This list makes sense with the fuel tank selector valve, or my understanding of it. This all lines up with hatzies Dual Tanks Theory of Operation thread. So maybe there was an issue and what I am seeing is the PO bypassing an existing issue to get fuel to return to the tank?
I assumed fuel doesn’t go into a plastic canister filter and then back out but I might be wrong?

Someone show me the light please!!

I am certainly getting under the truck yet again tonight but wanted to make 100% sure I am correct on what I think I know before I tinker with it.

As always thanks for the help!

Edit: guess I am an idiot because it cant be plumbed any other way than 1/4" off the mechanical. So I wont be messing with anything. Still don't quite understand how 5/16" is the return line when it runs from the passenger tank to the canister though.

You really want to get this correctly plumbed. Fire is an unpleasant way to loose your toy.
Filling the LH tank with the return from the RH tank is extremely bad.
Likewise routing the return to the vapor can is extremely bad too.


The return and supply from the LH tank will go on the LH barbs of the valve and the RH set on the RH barbs.
The engine hoses are all by their lonesome on the other side of the valve.
Look at the cutaway pic in the theory of operation and open the Installation PDF from Pollack that I linked in that post.

The senders have three connections.

1. Supply: Identifiable by a long hardline in the tank with a mesh sock at the bottom near the float. Likely the 3/8" line. Use SAE J30R9 hose and spring band clamps... small diameter Ideal worm clamps are evil.
2. Return: Short section of straight steel line reaching about 1/4-1/2 of the way down the supply leg. Likely the 1/4" line. Use SAE J30R9 hose and spring band clamps.
3. Vapor: Terminates in a liquid separating unit immediately under the sender top. Usually 5/16". Tee this and run both to the charcoal can vapor connection. Use SAE J30R7 hose and spring band clamps.

The mechanical fuel pump has three connections.

1. Large barbed is the Supply line.
2. Small barbed is the return line.
3. Threaded inverted 45°flare is the carb feed.

Here's a fuel line layout from LMC Truck...