Fuel return help needed

[JoshuOne]

Greetings. I bought a 1977 K10 with two tanks, but only the passenger side was hooked up, the drivers side was completely disconnected. I'm having some fuel dilivery issues and went to replace some of the rubber. My issue and I haven't been able to find a solution is that the sender on the working tank has two lines, the delivery line is fine and goes right to the carb, but the return? line is rotted at the the sender and the other side of the run in the engine bay it is just an open steel line connected to nothing
. Please help me, if you know, where this return line is supposed to go in the engine compartment. I suspect that my fuel delivery issue has everything to do with that line being rotted and open. Perhaps gas is even evaporating through it? I hope you are able to help with a solution, even if it is simply capping that line. Thank you so much in advance and I look forward to hearing from you.
Best regards
JoshuOne

 

[germando]

The return line should run to the pump just like the feed line. They are both rubber that convert to steel at the back of the engine, then back to rubber to connect to the fuel pump.
I just replaced mine as well.

G

 

[JoshuOne]

I appreciate your response, but yeah, I thought it should, but no. The mechical fuel pump only has one line in and one line out... The return line to the tank ends open and unconnected to anything on the drivers side of the motor. Hopi g someone knows where it's supposed to go when it's like that. Thanks,

 

[RaisedK5]

Driver side line is to the Evap can on the core support.

 

[Bextreme04]

Greetings. I bought a 1977 K10 with two tanks, but only the passenger side was hooked up, the drivers side was completely disconnected. I'm having some fuel dilivery issues and went to replace some of the rubber. My issue and I haven't been able to find a solution is that the sender on the working tank has two lines, the delivery line is fine and goes right to the carb, but the return? line is rotted at the the sender and the other side of the run in the engine bay it is just an open steel line connected to nothing
. Please help me, if you know, where this return line is supposed to go in the engine compartment. I suspect that my fuel delivery issue has everything to do with that line being rotted and open. Perhaps gas is even evaporating through it? I hope you are able to help with a solution, even if it is simply capping that line. Thank you so much in advance and I look forward to hearing from you.
Best regards
JoshuOne

My thought is that someone put in the wrong pump or wrong sending unit, or both. If you had a return line system from the factory(not all did), you should have a 1/4" return line and 3/8" feed line running from the switching valve to the pump area. It will be steel hard line and will bend out from the frame near the passenger side tank. If you had a charcoal vapor canister equipped from the factory, you will also have a 5/16" hard line running from the same area all the way forward and across the core support to the passenger fender well. This line would have connected to a charcoal canister to vent the tank(again, not all had this.. it mostly depends on if you have a high GVWR and federal/cali emissions).

Now for the sending unit and pump. If you have TWO hard lines that end in the pump area, you should have a three port pump. This helps to stop vapor lock in hot climates by constantly circulating more fuel through the return line rather than dead heading it. The three port pump needs to be paired with a three port sending unit. The sending unit will have a 3/8" feed outlet, a 1/4" return, and a 1/4 or 5/16" vent line. If you are not venting the tank, you will have issues with pressure building up in the tank and pushing too much fuel or with vacuum building up as you drive and stopping fuel from flowing once it gets too much vacuum for the pump to overcome. If you don't have the 5/16" hard line and charcoal canister in the engine compartment, then the vent line just goes to a bobble check valve similar to what you have on a diff vent.

The two port sending unit is just feed and vent, no return. You can identify which port is which by looking at how it goes into the tank. The vent will have a little plastic check valve piece on the inside. Return is just a short pipe that ends right inside the tank, and feed goes to the bottom of the tank with a filter sock on it.

 

[JoshuOne]

Yes, something got switched incorrectly before I got it. Both the pump and the sending unit only have two lines, the drivers tank is disconnected completely, as well as the switching valve. The second smaller line from the sending unit ends in a hard line by the drivers side of the engine bay just above the brake distributor block. Would it be fine to leave it, just replace the rotted rubber, or put some type of cannister there or maybe something else? The least expensive solution is probably the best for me right now.

 

[Bextreme04]

Yes, something got switched incorrectly before I got it. Both the pump and the sending unit only have two lines, the drivers tank is disconnected completely, as well as the switching valve. The second smaller line from the sending unit ends in a hard line by the drivers side of the engine bay just above the brake distributor block. Would it be fine to leave it, just replace the rotted rubber, or put some type of cannister there or maybe something else? The least expensive solution is probably the best for me right now.

I would put at least a one way check valve on it to keep debris and bugs from getting in there and clogging it up. You will get a fuel vapor smell from having just the open line. It would have originally run there to a charcoal canister to control the smell and recycle the fuel vapor back into the engine. The only downside to the current setup will be the possibility of vapor lock when the temps get high and especially if you are at altitude. You probably don't need to worry about it until you run into that situation.. but it will be a pain in the rear when it does show itself.

 

[JoshuOne]

Hi, thank you for your response. So, I am at about 6600 feet and it does get pretty warm here... Is the solution to get a fuel pump amd sending unit with three ports apeice? Would the third port in the sending unit simply be attached to a little filter like they sell for replacing pcv valves or would it be more complex? I am grateful that my 77 isn't my only vehicle or I'd be stuck and stumped. Thanks again!

 

[Ricko1966]

If you are going to leave a vent line open put a fuel filter on it,the tank can vent,it can't create an airlock and starve for fuel,and dirt can't get in. A clear plastic one would be my choice.

 

[Bextreme04]

Hi, thank you for your response. So, I am at about 6600 feet and it does get pretty warm here... Is the solution to get a fuel pump amd sending unit with three ports apeice? Would the third port in the sending unit simply be attached to a little filter like they sell for replacing pcv valves or would it be more complex? I am grateful that my 77 isn't my only vehicle or I'd be stuck and stumped. Thanks again!

Yep, three port pump and three port sending unit. I explained in detail what that plumbing should look like in Post #5

 

[SquareRoot]

You have two tanks but make no mention of a switching valve. Did I miss something?

 

[JoshuOne]

The driver side tank and switching valve were disconnected long before I acquired this gem... And thanks again all, I will keep you posted.