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Pressure in the gas tank...how much should there be?

Discussion in 'The Garage' started by Lotsa_Faith, May 10, 2003.

  1. Lotsa_Faith

    Lotsa_Faith 1/2 ton status

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    whenever i open up my gas cap to fill up, theres so much pressure that it kinda shoots the cap off when i take it off. then after i fill up, the truck will cut out for the next 30 minutes or so, then run fine. do you think its relying on that pressure in the tank to push the fuel to the engine? if so then ill get a new fuel pump, but i dont have alot of money layin around so i don't wanna replace something i didnt need to...
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Total guess here, but assuming you have the diesel still in the truck, are you running the right fill cap?

    Again *assuming* that the diesels (or at least military diesels) didn't have EVAP, if you are running a newer cap, they don't "vent" until something like 13-16PSI.

    I wouldn't suggest a rag in place of the fill cap, so if you can get your hands on an older gas cap, try it. (or the correct diesel one) Of course, with diesel, I don't think a rag as a gas cap will make a bit of difference since the diesel isn't nearly as dangerous as gas in that respect, but its still not safe I'm sure. You know, for the errant cutting torch and what not. /forums/images/graemlins/smile.gif
     
  3. Lotsa_Faith

    Lotsa_Faith 1/2 ton status

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    no its got a 350 in it...
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Then it *really* sound slike you've got the wrong cap on it.

    You've either got to have EVAP/vented tank, or an older "unvented" setup with the matching older "vented" gas cap.

    Friend has a 1973 pickup with the new style gas caps on it, and it will spew gas on you if you drive it or leave it in the sun, and open the cap, from pressure buildup.

    Older tank caps vent at something like 3psi, but with EVAP, all vapors from the tank are collected with the EVAP cannister, and the cap is ONLY vented (and at the much higher pressure) in case the EVAP system becomes plugged, or else you'd blow a line, seam, or whatever if the EVAP got clogged and the tank couldn't vent.
     
  5. Thunder

    Thunder 3/4 ton status

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    Just get a new gas cap for your vehicle. you either have the wrong one or the vent in the cap is not working.
    Or you can do a hillbilly repair and drill a little hole in the cap /forums/images/graemlins/eek.gif
    Just to see if it fixes the problem.
     
  6. MousePowrd

    MousePowrd 1/2 ton status

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    The vent line to the charcoal canister (if they did that in 85, I think they did) may be plugged or kinked.
    Also there may be a check valve inline that is stuck closed
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I took the charcoal canister and that line completely off my truck when I did the frame off and it didn't cause any issues.

    I suggest leaving your gas cap loose from now on. Free vent!!
     

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