Dual Tank Question

[Russell]

I asked in the engine and drivetain forum too, but I want to do this today, so I'm needing an answer

Hey all, My truck has return lines on the fuel tanks, but my tank switch is no good. I have another one, but it only has provisions for the line going to the fuel pump. Can I just put a Y-pipe into the return line setup and hook all three together? I would guess that the fuel would be more likely to run to the tank that is being drawn from due to the slight vaccum that would be made from doing the fuel drawing.

Any thoughts about this?

[1972C10]

That might work but it would split the return fuel You might get a fuel pump without a return and just do away with the return lines.

[mike reeh]

I agree w/ 72C10.. It wont work like you think. If youre on a budget just get a new fuel pump for a truck w/o the return (about $20) and do away with the return altogether.

Better yet, leave the fuel pump and get the correct selector valve

mike

[Russell]

So why exactly won't this idea work? What is the theory behind this return line?

[1972C10]

Excess unused gas returns trou the return line Be better off to cap it off rather than try to tee it .

[Russell]

Ok, I'm not quite understanding here, if it is just excess gas, it shouldn't matter which tank it dumps into, having the T shouldn't mess with the pressure or anything would it? I've got a single line fuel pump on my longblock, but the fuel pump on my truck was just installed like 5000 km ago...

[1972C10]

Well i guess it would work but if it was mine i would either cap off the return line at the fuel pump or get a non return line pump ..

Thats if i couldnt get the proper switching valve .

[Russell]

The proper switching valve is 80+ bucks up here, I would rather install the metal T pipe I already have for it, but if its gonna affect safety I don't wanna do it...

[1972C10]

Right.. Well just get a 9.99 autozone lifetime warranty fuel pump without the return line or cap your current return line At the pump Althou pumps are cheap and be way better to just get a non return line pump

[mike reeh]

Do you need dual tanks that bad? If you do, then you probably fill both tanks when you fill up. What happens when the fuel in the return line takes the path of least resistance and starts filling up the full tank? Its unsafe..

as for "slight vacuum" in the tank being used, thats boloney because both tanks are vented and should have a slight vacuum anyways from the charcoal canister line @ the carb.

The only reason I dont say "just cap the return line" is because I dont know if that will mess with the pressure regulation.. It might boost pressure @ the carb, overpowering your needle & seat, thus creating another hazard & more headaches...

but I could be wrong. Maybe it will cause no harm no fowl. If you do cap the return line @ the pump, make sure you put a pressure guage on the carb fuel line! 5-6psi max or you will have problems.

russell i dont know why you dont just swap the pumps if its that important to you..

Orr just run off one tank until you can afford the correct selector valve. I'd watch ebay or gmpartsdirect.com...

Can you post a picture of your selector valve? I have one from a 84 GMC C25 with dual tanks that I will never need. I might part with it cheap if its the right one for you. Its in the rafters in the garage though, but I remember what it looks like if you post a pic I'll identify

mike

[1972C10]

ive plugged them off in the past as cheap as they are it would be better to get a no return line pump

[Russell]

I don't really need it that bad, but I would like to have them setup as I have 40 bucks worth of gas going to waste in that other tank... I'll snag a picture of the valve tonight for you.

[79BIG10]

Easy fix here. Get under the truck and swap the lines on the valve itself. It will be the two larger lines on the right side of the valve. Swap these and the valve will be taking in from the driver side tank then. Also read this to help you find out for sure what's wrong with your truck's problems. Does your gauge move when you switch the tanks? Have you been kicking or moving anything near your fuse block panel? Just a few questions to help diagnose.
Now here's a couple ideas:
On your interior valve switch replace it. To me it sounds like you have a bad switch. I got mine with cover for like $10 from the dealer. Don't use the Auto Zone stuff. The dealer is a couple bucks more but why waste on something that isn't to GM specs? To take off the switch and cover the 2 nuts have to be taken off the rear of the cover behind the dash. Best way is to take out the ash tray and it's much eaier to get to then. Don't use the Auto Zone stuff. The dealer is a couple bucks more but why waste on something that isn't to GM specs? While you're there with the plug off let's see if we're getting power to where it needs to be.
From the 3 o'clock position this is #1 wire then so on till #5 for reference.
#1- Ignition wire (pink w/ black stripe)
#2- Valve wire (lt. green)
#3- Tank Aux. (lt. blue)
#4- Gauge (tan)
#5- Tank Main (tan w/ white)
#6- Not used
With the ignition on you should get power with the #1 slot. If not check the pink w/black wire by following it to the fuse panel. Mine was connected with a male spade connector to a IGN slot. This way it's only powered when ignition is on (neing not running). Also you should have a light when testing for the #4 gauge as well (assuming it the #1 is hot).

If this doesn't solve it then take a test light to your fuel valve itself. It is located on the passenger side close to where the cab and bed meet. There are 3 different setups on the valve. They are 3 ports (fuel) 1 wire, 6 ports 1 wire (mine) and 6 ports 6? wires. You need to see which one this is. On the 3 & 6 ports with 1 wire, the green wire, attaches to a bolt coming from the valve itself. This is what powers the valve to flip from the one tank sending hose to another. When you have the selector valve on the left side (with ignition switch on and for safety engine not running and emergency brake on) the green wire will have power (where test light comes in). When you have it on the right side of the switch the wire will have no power. This is why I like to run on my right tank more often than my left. Now if you don't have any power to that switch under the bed, you need to backtrack (next section). If you do have power then you need to test the valve itself. With the ignition on engine not running and emergency brake on (safety first) take the green wire with connector to the "bolt" that is the connection on the valve itself. As long as you have power (with the interior switch flipped to the left side) you should hear the valve turn to the left tank. It sounds like a "click" almost. If you have power to the green wire but the valve is not changing tanks this is your problem. Replace the valve (I got mine for $70 from a AC Delco parts warehouse) and while you're there replace all the fuel lines as well. It's cheap insurance. Just make sure to label the hoses so you know which goes back on where. With 6 hoses on mine it was a job to make sure everything was on right.
On the firewall driver side look for a 4 wire harness with a bulk connector (looks like a connector that has a rubber boot) It will have 2 tan wires a green and a lt blue wire. This is where the tanks and selector valve wire come from the interior switch. If this is tight and no corrosion then we'll need to rethink this. Hopefully this works.
If you have a 6 wire then let me know and I'll try to find a spec for that then. I have't messed with that wire harness yet at the tank selector valve itself.

[Russell]

Alright -- Big post, lol!

I've got power down to that switch, the solenoid works, but has a broken stud. Its a 6 port valve with one wire. Right now I have bypassed the valve and am running off only the left tank. None of the trucks that I've seen at the local wreckers have had the right kind of valve, which is all I am needing.