Mysterious fuel lines

[Mysta2]

I've got the bed off my '79 (with electric fuel pump) and the filler neck is trash. It's rusted through in a couple of pinhole spots. I've placed an order for a new one off Ebay, but I can't figure out what one of the lines on the old one is for. The new one does not have it, nor the plate that it's mounted to.

 

There's the feed line that goes straight to the frame rail mounted pump

 

There's another line that comes from under the cab and goes to the side of the tank (I assume this is the return line)

 

There's a third line that goes to just under the gas cap (vent line)

 

And there's a fourth line that comes from under the cab, loops up near the top of the fill tube and comes back down, through a black plastic filter looking thing and back to the top of the tank.

 

What's that fourth line? something to do with emissions? I suspect it may be related to the line on the drivers side of the engine bay that has a wooden dowel rod shoved in the end of it.

[datzenmike]

The one with the 'fuel filter looking thing' is the tank vent line. The 'fuel filter looking thing' is a one way valve to allow fumes out but prevent fuel getting out in the event of a roll over. Gas fumes from heat or evaporation go forward and are stored on a charcoal canister. Next time the engine is started manifold vacuum draws them into the engine to be burned.

[Mysta2]

Cool, thanks. Then what's the one that dumps into the filler neck just below the cap?

 

Filling vent? I imagine the vent you're talking about might not be fast enough to work as the fill vent, it's pretty small.

 

My Ranchero used to puke out all its gas if you tried to fill it too fast.

[datzenmike]

Probably to let the air bubble out from the top of the tank as the gas fill up.