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Fuel return line...

Discussion in 'The Garage' started by Topdown, Feb 18, 2004.

  1. Topdown

    Topdown 1/2 ton status

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    I was looking under my truck and found a hard line, roughly the size of my fuel line, open, sitting on the frame-rail... no cap, no rubber line attached to it... nothing.

    Is it possible that my 1972 K5 has a fuel return line?
     
  2. crawford

    crawford 1/2 ton status

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    My '72 has the exact same thing. I have a electric fuel pump instead of the mechanical one now, so that may be why. It has been on my list to figure out what the deal is and get rid of it if I don't need it.
     
  3. BobK

    BobK 1/2 ton status

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    It's for the charcoal canister.It's a gas tank vent line(emmision device).
    Goes from the tank via a hard line to the canister that should be located on the passenger fender,below the battery tray.
    The hard line stops and a rubber line would go from there to the canister.
     
  4. gravdigr

    gravdigr 1/2 ton status

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    If you do run an electric fuel pump it is a good idea to use a return line. The constant fuel flow through the pump keeps it cool which is a good thing.
     
  5. BobK

    BobK 1/2 ton status

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    Here's a pic I took while installing my electric fuel pump when I did my TPI install.
    [​IMG]
     
  6. Topdown

    Topdown 1/2 ton status

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    so since I have no charcoal canister anymore... can I use that as a fuel return line?
     
  7. Burt4x4

    Burt4x4 3/4 ton status

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    That ie what I am thinking of doing. My canister is still there but I won't be using it for emisions anymore. I would think that it should work great as a return line.????
     
  8. Topdown

    Topdown 1/2 ton status

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    it seems to make sense to me... if its a straight shot back to the fuel tank and there is no canister in the way. Is there a valve or something that would impede the flow?
     
  9. Burt4x4

    Burt4x4 3/4 ton status

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    I don't think so? It's just a vent for the fumes to go into, as far as I can tell anyway? The MPFI I am putting in requires a return line so My plan is too use that line.I will blow some air thru it with my compressor just too make sure it is clear /forums/images/graemlins/thumb.gif
     
  10. Topdown

    Topdown 1/2 ton status

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    cool /forums/images/graemlins/thumb.gif that may solve the problem super fast and easy... when you blow some air in it, post back up what you find. I'll buy you a beer some day /forums/images/graemlins/woot.gif
     
  11. BobK

    BobK 1/2 ton status

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    haven't followed that line back to the tank.If you use it as a return make sure it doesn't interfer with the venting system of the tank.
     
  12. gravdigr

    gravdigr 1/2 ton status

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    [ QUOTE ]
    haven't followed that line back to the tank.If you use it as a return make sure it doesn't interfer with the venting system of the tank.

    [/ QUOTE ]

    Exactly. Make sure you have a vented gas cap. Usually stock caps are sealed so the vapors have to go to the charcoal canister. The last thing you want is gas fumes to build pressure in your tank. I just put in a new tank and sending unit in my '79 and I seem to remember there being some type of valve at the vent port that goes to the charcoal canister. But my sender had a separate nipple for a return line.
     
  13. Burt4x4

    Burt4x4 3/4 ton status

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    Hmmm, well on my 72 I have 3 other tubes connected to my tank besides the fuel line. Two goto the metal tube thing in the rear drivers side quaterpanel near the tail gate. The third is the one we have been talking about. I'm not sure if the meatal tube thingy is a vent or some kind of ?????
    I agree there must be a vent, wait I think the filler tube has a vent tube also?? Oh now I gota go look.....
     
  14. Topdown

    Topdown 1/2 ton status

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    the filler tube is a tube within a tube. I think thats where it vents... aside from that, I am not 100% certain that it even really ever seals with my gas cap on /forums/images/graemlins/grin.gif

    It would be so kick-ass if that extra tube was able to be used as a fuel return
     
  15. gravdigr

    gravdigr 1/2 ton status

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    There is a vent in the filler neck tube, but that is only used when pumping gas. Once you put on the gas cap that vent gets covered. My sender had 4 lines coming out of it. 1 was the vent to the filler neck, 1 was fuel supply, 1 was fuel return, and 1 was vent to charcoal canister.
     
  16. Topdown

    Topdown 1/2 ton status

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    did you ever figure out if it has a vent?
     
  17. Burt4x4

    Burt4x4 3/4 ton status

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    Well that pipe that is mounted next to the filler neck is sealed? Not sure what it's function is? The filler neck is vented but only when the cap is off.
    I still don't know for sure what I am going to do for a return line but I will let you know what I do. /forums/images/graemlins/thumb.gif
     
  18. BurbinOR

    BurbinOR 3/4 ton status

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    [ QUOTE ]
    Well that pipe that is mounted next to the filler neck is sealed? Not sure what it's function is? The filler neck is vented but only when the cap is off.
    I still don't know for sure what I am going to do for a return line but I will let you know what I do. /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    Just FYI for you guys - I did a new return line on the TPI406 setup for my K5 with a braided stainless hose.......there's no pressure to worry about, mainly just have to watch for routing it properly to avoid abrasion and catching it on things. Just tuck it up inside the frame rail and you're good to go. Pic - you can see the hard plumbed line I did for the pressure side - new 3/8" all the way from the filter to the factory TPI hose hookups.
    [​IMG]
     
  19. BigJohnson

    BigJohnson 1/2 ton status

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    BurbinOR, what filter were you running in that picture? I am about to re-plumb my rig for EFI and I am trying to find a good inline filter to use.

    Thanks
     
  20. ColAdo82K5

    ColAdo82K5 1/2 ton status

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    Looks like part number FF504....GM used them for lots of applications for a long time. even the new 8.1 litre uses that filter.

    Blake
     

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