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Gas tank venting problem

Discussion in 'The Garage' started by clarkjw24, Apr 18, 2005.

  1. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    I've recently install tbi on my K5. I drove it about 20 miles today pretty hard and fast. When I pulled up in the yard I notice a liquid pouring out of the front. I thought great I've blown a radiator hose. After close inspection and a sniff I realized it was gas coming from the vent tube. I released the gas cap/pressure and it stopped. I'm thinking that I need to switch my vent and return line at the sending unit. What do yall think? I'm at work now until midnight so I'm trying to think out loud about this. I've got to have it fixed by Wed cause she'll be loaded up and on the way to ECBB thurs morning. :xmas:
     
  2. R72K5

    R72K5 Banned

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    the tank is not supposed to be building such pressure

    make sure vent line is not plugged off somewhere, the middle sized one along frame rail up to charcoal canister and teed to engine vacuum
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Yep, I think of the main causes of overpressure problems (my front diff, others fuel/vent lines, etc) is those mud dauber wasps or whatever getting in the lines.

    If you've got a vent line in place, first thing I'd do is disconnect it as far away from the tank as possible, and see if you can get air through it.

    If you switched to TBI, you shouldn't have a problem with the lines being reversed, only the inlet and return lines are threaded fittings.
     
  4. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    The pressure was releasing from the vent line that went up to the front so its not clogged. Now heres the tricky part, I used a sending unit from a truck saddle tank setup, it doesn't have the big vent (filling vent) made into the sending unit like a K5 tank. So I drilled a hole in the top of the tank near the main filling tube and put a fitting in it and hooked up the big vent. When I walked around to open the cap today, I could here the pressure hissing at this hose. Maybe I've got a little kink or its collasping, I've got a 2" body lift so I looked at it but it seemed fine. The big vent tube that runs along the filler neck goes into the filler right? This is the one that I drill out a fitting for. Thats why I'm thinking maybe I've switched the vent and return at the sending unit. The tank only had a quarter of gas in it so if I had the vent small vent tube right it wouldn't be able to pull gas. Its at the top of the sender not in the bottom of the tank, right?
     
  5. spearchucker

    spearchucker 1/2 ton status

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    The vent tube on my sending unit (89 tbi) has the return line going to a tube that extends about half way down inside the tank. The vent tube ends at the top of the tank. There is no way for fuel to get up to the vent tube unless the tank is over filled ... or you have the lines switched. :blush:
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    I guess maybe I'm not understanding...vent line runs up to EVAP cannister which runs to TB *normally*. If you didn't route the vent that way, then that won't mean much. I'm just imagining a vent line coming from the tank running up front somewhere, to "vent". If the line is leaking gas because of pressure before the actual open end of the vent, I'd be imagining a restriction past wherever the leak was occurring. Again, there should be *3* lines running up to the front, and yes the *fill* vent just runs back into the fill neck.

    If you have the lines reversed, blowing into the vent line SHOULD let you hear the bubbles you create if the tank is near full. I know for a fact the vent line fitting is flush with the sending unit (no tube) so you couldn't fill the tank up enough to get fuel into it, at least in common usage.
     
  7. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    I'm sorry not pressure but liquid (gas) was pouring from the vent line going up front which is not conected to the canister but I does have one of those vent caps on the end of the hose.
     
  8. Fierospeeder

    Fierospeeder Banned

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    follow the return line from the engine to the gas tank and see if you have it hooked up correctly. It is possible that you made the return line feed into the vent line up front.


    Also, make sure your filler hose is in good condition.
     

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