Fuel tank pressure? | FerrariChat

Fuel tank pressure?

Discussion in '206/246' started by need4speed, Jul 1, 2013.

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  1. need4speed

    need4speed Formula 3

    Nov 3, 2003
    1,616
    Pacific Palisades
    Hi Everyone,

    I've been smelling fuel fumes for a long time and it's finally been fixed. A small crack in one of the hoses. But an interesting side effect of the fix is that when I open the fuel cap, there's a bit of pressure in the system. As soon as the cap gets near the last threads, it literally pops off. Is this normal?

    I've owned the car for a number of years and I don't ever recall that being the case. If it's not normal, is it something to be concerned about?

    Thanks
     
  2. dignini

    dignini Formula 3

    Aug 21, 2005
    1,348
    NJ
    Full Name:
    Luigi Marazzi
    I do not recall ever noticing that.
    A crimped hose or blockage?
     
  3. Pantdino

    Pantdino Formula 3

    Jan 13, 2004
    2,069
    Full Name:
    Jim
    I have had that happen. If you fuel the car in cold weather then remove the cap in hot, the fuel vapor inside the tank will have expanded because of the temp change.

    When you had the cracked hose it was allowing the pressure in the system to escape so it did not build up.

    Modern fuel systems have a one-way valve to allow air in (so the fuel tank won't deform / collapse into itself as fuel is used) but not out because that would be smog-causing unburned fuel vapor. If your charcoal canister is still present it is supposed to soak up fuel vapor and release it into the intake system when the car is run.
     
  4. solly

    solly Formula 3

    Jun 2, 2001
    1,148
    Westchester NY
    Full Name:
    Dr. Steven S.
    It's a warm weather phenomenon. Should go away when temps are back in the 60's or lower. Pantdino is correct. Gasoline boiling point begins at 100F, a temp. easily reached in a closed container on a 90-95F day like we have been experiencing here in NY for the past week or two.
     
  5. TonyL

    TonyL F1 Rookie

    Sep 27, 2007
    4,202
    Norfolk - UK
    Full Name:
    Tony
    tanks are vented from a pipe taken off the fuel filler pipe so there should be no back pressure.
     
  6. need4speed

    need4speed Formula 3

    Nov 3, 2003
    1,616
    Pacific Palisades
    That's what I thought. Thanks for all the replies guys.
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,826
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Only on a euro version - a US version has a more complex system (sealed at the filler neck & cap).

    A small positive pressure is "normal" on a US version as the check valve inside the 3-way valve has a non-zero opening pressure (also, a euro properly "converted" for US importation would too). However, these systems often get removed/hacked/modified without the Modifier understand how the system is designed to work. Do you still have all the components+plumbing shown in this SPC figure?:

    Ferrari 246 Dino Parts : Table 49 - FUEL SYSTEM (VARIANTS FOR USA VERSIONS)

    The critical gizmos are item 8 (the 3-way valve) and item 12 (the charcoal canister); however, if it's a converted euro, sometimes the valving in item 8 is built into the aftermarket charcoal canister.
     
  8. need4speed

    need4speed Formula 3

    Nov 3, 2003
    1,616
    Pacific Palisades
    Hi Steve,

    My car is a non-converted US car. And as far as I know, I have a completely stock setup. I'll confirm this with my mechanic the next time I'm in for a service.

    Thanks for the reply,

    Manny
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,826
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Don't quite follow this description -- are you saying:

    1. It is stock US version that has never been modified, or

    2. It is a euro version, now in the US, that has never been modified, or

    3. Something else?
     
  10. need4speed

    need4speed Formula 3

    Nov 3, 2003
    1,616
    Pacific Palisades
    #1
     
  11. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,826
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Then all is probably OK (if all the components + plumbing are still present per the SPC figure).
     

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