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WTF? my sending unit has 4 connections???

Discussion in 'The Garage' started by mechted, Aug 6, 2005.

  1. mechted

    mechted 1 ton status Premium Member

    Oct 19, 2003
    Likes Received:
    Granbury, TX
    ok, was working on my 73 today (shackle flip to remove PO's stacked blocks... :doah: ) and when i dropped the tank i was confused as hell to find 4 connections coming out of the sending unit...

    Pic: http://community.webshots.com/photo/221327895/415335227HnbTeo#

    and thanks to the PO, everything was creatively replumbed for me :mad: so anyways heres what i could figure out:

    ~1/2" OD (far right) = Gas Filler Vent Line
    ~1/4" OD (center w/ hose) = Supply Line
    ~3/16" OD (center w/0 hose) = ???
    ~1/8" OD (far left) = ???

    So, one is the return line, i'm thinking the 3/16" OD one... but what is the other one for? Another vent?
    this is on a 73... and as far as I could tell no one had ever dropped the tank before, just played with the plumbing forward of the tank.
    Anyone know about this?
    Last edited: Aug 6, 2005
  2. dremu

    dremu Officious Thread Derailer Premium Member GMOTM Winner

    Feb 27, 2000
    Likes Received:
    East of San Francisco
    Crap. I just look at one today, I should know this.

    There should be two lines coming from the engine compartment, one larger than the other. The larger one is the fuel supply, and the smaller one is the fuel return.

    There also should be a vent tube in the filler neck, so the very large one, and the little one next to it, both go up to the side of the truck.

    OTOH, I've also seen (i.e. just this afternoon) a vent-to-atmosphere, with the same vent that you find on a tranny or t-case or axle.

    If nobody can tell you for sure, I'll post pix in the morning.

    -- A
  3. pauly383

    pauly383 Daddy383 Staff Member Moderator

    Jul 22, 2001
    Likes Received:
    Mesa , Arizona USA
    Betcha its a newer tank .

    My 83 tank , and the other 83's tank I just got rid of , had :

    1 line for Evap Can
    1 line for Fuel pump supply
    1 line for Fuel pump return
    1 line for filler vent

    and of course the big fill tube .

    Myabe they had them earlier , Daves 74 in my yard has a Evap can , but I don't recall a Fuel pump return . Maybe one is for vent prior to return line .
  4. PsychoticDeadGuy

    PsychoticDeadGuy 1/2 ton status

    Jan 8, 2005
    Likes Received:
    Fairfield, California
    the 3/16 is the fuel line...
    the 1/8 is the return line from the engine...
    the 1/2 is the filler neck line...
    the 1/4 is the vent tube that runs next to the filler neck tube...

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