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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: jon316 on February 28, 2020, 04:51:41 PM
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Hi everyone I am in the middle of an LS swap, but these questions although do have to do with the swap doesn’t really pertain to it. I have 1981 c10. The passenger tank was already disconnected. So I am removing it. Removing the makeshift primer pump it had and running a new external pump. My first question is, I see THREE lines coming from my tank to the diverter valve. I know which is the feed, and return, but the third, is what the vent? It goes to the valve to so no idea what it does.
Second question is, which wire is for the gauge? Is it at the valve or does it go straight to the gauge?
(https://uploads.tapatalk-cdn.com/20200228/9c825ad4e6b35e35f66ba51238621de1.jpg)(https://uploads.tapatalk-cdn.com/20200228/6b9f1d2d20390d1b9cf6f523af714c8b.jpg)(https://uploads.tapatalk-cdn.com/20200228/c1f8fc6ff5cad3cf86e6dafe3ccc34a0.jpg)
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My first question is, I see THREE lines coming from my tank to the diverter valve. I know which is the feed, and return, but the third, is what the vent? It goes to the valve to so no idea what it does.
Second question is, which wire is for the gauge? Is it at the valve or does it go straight to the gauge?
The three lines exiting the fuel tank should be: Fuel Supply to Pump = 3/8", Fuel Return from Pump = 1/4", Tank Vent to Carbon Canister = 5/16".
Only the Supply and Return lines should route through the tank selector valve. The Vent lines from both tanks should tee together and then run directly to the carbon canister.
(https://uploads.tapatalk-cdn.com/20200228/6b9f1d2d20390d1b9cf6f523af714c8b.jpg)
The center pink wire in the selector valve connector (second terminal from the right in the foregoing image) should run directly to the dash gauge. See the auxiliary fuel tank wiring diagram below.
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Thanks! Wondering what to do with that vent as I don’t have a canister now.
That plug is the one on the valve. Since I am removing the passenger side aux tank, not sure what to do. I still have a switch in the cab. Guess I can remove all of that. Just confused on what to do with that wire. Technically even if the valve is gone would it still read the proper tank(left) as long as the switch in the cab is on left?
Think it’s sometimes harder when you pick up on someone else’s project when it’s halfway done!!
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Not difficult. The fuel level wire from the tank sending unit you keep should splice directly to the wire that runs to the dash fuel gauge.
You will regret eliminating the carbon canister. It captures the noxious gasoline vapor emanating from the fuel tank so that gas odor doesn't foul the air you breathe or saturate your garage with explosive gases. Especially rethink your decision to eliminate the canister if you have any kind of pilot light in your garage!
The fuel tank must be vented for fuel to draw properly. If you continue the conversion w/o a canister you will need to install a vented fuel cap, in lieu.
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Ok so been having a crazy schedule. I’m cutting up the lines to run them to the fuel filter regulator.
Just to be sure because these lines were a mess. I have smallest on top to biggest on bottom...top is return, middle is vent, and bottom is supply?
(https://uploads.tapatalk-cdn.com/20200318/aa81f6543afb47c79d61d3e1ad86a227.jpg)
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When I was figuring out how much rubber fuel line and how many clamps to update everything on my truck I made this diagram (attached). It should be similar to the setup on your truck.
Bruce
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Really late just got an email from Tapatalk and saw this. I know little but have a pickup with dual tanks. Put in tbi engine and had to go intank pumps. Did a bunch of ohming and with a carling constant on dpdt switch from ebay. The way I remember, Two wires side by side, Power on wire ground other left tank, switch polaritys and it switches to left (typo meant right) tank. From the plug by the fuel switch run the right power to right tank pump and left power to left tank. When you put power to the fuel switch to open the right side it also powers the right pump same on the left side. Note that the switch has constant power vs. factory momentarily switch. Have had trouble though. Not sure on the gauge but got that going as well.
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Green or pink I’ll look.