Dual gas tank switching problem

[dyno]

Hi,

I've been fighting my dual tank selector valve on my 1980 K20 for years now. The valve has 6 ports; 4 in and 2 out. I have searched everywhere and cannot find a replacement valve that has a single wire like mine. All 6 port universal replacement valves have a multi pin connector.

So, my question is, what's the purpose of the extra 5/16 line on each tank? Could I cap those off and use a 3 port valve?

Thanks.

[menace121978]

how many ports does your sending unit have? mine have 2 on each unit. 1 is for fuel feed the other is for a vent and emissions that runs to the charcoal canister. my switching valve has 3 ports and 1 wire. i picked this up at oriellys. the only reason for a 6 port is for returned fuel.(fuel injection) so... take a look at these pics. you can either plug off the extra sets of ports(as long as you dont have a return line from the motor/fuel pump and put a vent on the sending units (if you dont have a canister) and figure out the wiring. or go buy a new valve with 3 ports and 1 wire. i hope this helps!

[zac]

My '79 has a single wire just like yours. The right tank is unusable right now, so I've just been using the left. After troubleshooting and repairing the fuel gauge, the selector valve started getting ideas, and would just randomly cut off the fuel. My quick assesment of the fuel lines was that the smaller one is the return line. I can tell you that it had fuel in it, because it got all over my face while I was quickly bypassing the valve with some steel line and hose clamps. My plan is to eventually get the whole system working, so I would also like to see what people have come up with.

[Prong]

You need an ACDelco p/n #467513. They're still available for about $70.

[dyno]

Hi,

Thanks for you guys' help.

I tried to look up that AC Delco # it's available, but there was no description or pic for the part.

My valve has 4 in, 2 out- total 6 ports, single wire.

Can I block off the recirc. lines from the tank and fuel pump? What is the purpose of the fuel recirculating? If I can do that, I can use a 3 port valve.

Thanks.

[menace121978]

where does the 2 lines go from the switch valve? 1 to the fuel pump the other to.....??

because technically you just have to plug off the unused 3 ports without having to buy a new valve since its a single wire unit.

[zac]

Go to www.oehq.com and type in the part number. Says in stock for $77.15. There's a picture on the left you can enlarge. Looks like a winner. Thanks Prong!

[dyno]

Originally Posted by zac

Go to www.oehq.com and type in the part number. Says in stock for $77.15. There's a picture on the left you can enlarge. Looks like a winner. Thanks Prong!

Thanks! Yep, that's the one alright.

So I will probably order it and keep the lines the way they are.

But I'm still curious as to why they installed a recirculation system on these trucks?

[dan76]

Dyno: Most likely for the charcoal cannister. Allows fuel vapor/fluid to return to the tank.

Zac: Thanks for the site....already solved an issue for me. Also note the free shipping for 75$+ orders.

[sknights]

The return line (bypass) was added to prevent vapor locking.