Pressure in tank, fumes, explosions etc. | FerrariChat

Pressure in tank, fumes, explosions etc.

Discussion in '308/328' started by Helmut, Mar 26, 2010.

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  1. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    I am curious what you guys think of this. My 78 GTS restoration is coming to its final chapter and as I removed all the emissions equipment that may pump fumes etc out of the system I noticed that there is a lot of pressure building up inside the gastank. Usually when opening a gascap air is being sucked in from the vacuum thats been created but on the 308 I notice pressure build up which causes a lot of air to burst out when opening the gas cap.

    If the hoses like fillerneck etc would be leaking slightly, I would end up with gas fumes all over my engine compartment which wouldnt be good.

    I basically connected the three short little hoses that run from the passenger side gastank to the charcoal canister but I plugged the top end of the charcoal canister which usually has a hose connecting to the rest of the system.
    Would that system which runs from the passenger gastank via charcoal canister etc usually alleviate the pressure in the gastanks?

    Thanks
    Helmut
     
  2. BigTex

    BigTex Seven Time F1 World Champ
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    Well, your filler neck should NEVER be leaking!!
    I inspect that one twice a year and replace it if any cracking is observed...

    One end or the other of the charcoal can vents to atmosphere, don't recall which one...that's your troubles....

    Un plug that to let air into the tanks as fuel is used, the cap of course is toatlly UN vented, by design!!!
     
  3. BigTex

    BigTex Seven Time F1 World Champ
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    #3 BigTex, Mar 26, 2010
    Last edited: Mar 26, 2010
    I had your problem once and when the cap came off, the pressure equalizing the tanks set a GEYSER of fuel up the neck, into the air....

    Onto a hot car.....


    In the middle of no where.....

    You've never seen a guy push a car so hard in all your life!
    I got it off of the puddle of gasoline.

    I'll look at my 1977 diagram on the tubing and see if we can sort which ones need to stay coupled together, it's the RH fuel tank ones.....there's a check valve in that RH fender.
     
  4. 308 GTB

    308 GTB F1 World Champ
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    #4 308 GTB, Mar 26, 2010
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  5. BigTex

    BigTex Seven Time F1 World Champ
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    Well, studying that, how DOES the air replace the used fuel????
     
  6. 308 GTB

    308 GTB F1 World Champ
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    #6 308 GTB, Mar 26, 2010
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  7. BigTex

    BigTex Seven Time F1 World Champ
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    Ah....got it, the old "hot air surge tube"....he should check in there, for spiders!!!!!
     
  8. 308 GTB

    308 GTB F1 World Champ
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    That's why I keep my thermonuclear muffler in the garage with my 308, Bubba.
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #9 Steve Magnusson, Mar 26, 2010
    Last edited by a moderator: Sep 7, 2017
    You said "charcoal canister" (item B) in your description, but if you really meant the "liquid/vapor separator" (item D) -- yes, this would be a no-no (the single hose on top of the liquid/vapor separator must be somehow connected to atmosphere -- not blocked). In the stock set-up, the vapors (if any) exiting the top of the liquid/vapor separator pass thru the charcoal filter inside the charcoal canister before being released to the atmosphere (the charcoal absorbs any fuel in the vapor so only air exits the charcoal canister) or are ingested by the engine (when running). Here's the diagram of the 1978 US 308B/S fuel evaporation control system -- can you be more specific about how you've modified your system by marking up this diagram?
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  10. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
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    One of the vent lines on one of the canisters must be open to atmosphere. On my car, it was the bottom opening on the big can by the expansion tank that vented to atmosphere, but my car was not quite correct WRT to emissions routing, being a Euro conversion.

    I really don't think the CARB people will know which one is supposed to be open, so you can probably use any as a vent.

    Doug
     
  11. AZDoug

    AZDoug Formula 3

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    Mine looked like Steves picture, above, G was the atmosphere vent.

    Doug
     
  12. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    Thanks for all the good input!

    Yes Steve, correct, I am talking about unit D in the digram, not Unit B.

    So I connected the three small hoses from the passenger side tank to the bottom of Unit D but I plugged up the top end of unit D.
    I also plugged up all the lines from the intake manifolds that usually go to Unit B.

    What puzzles me is that logically thinking, since my gastanks are completely sealed off now, it would have to create a vacuum as the gas is pumped out of the tanks and into the engine but I find the exact opposite taking place. It creates pressure inside the gas tanks. ????

    Thanks,
    Helmut
     
  13. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    .... so if I would add Unit B and therefore have G as the vent but plug up the top of Unit B which usually goes to the Intake manifold, should that do the trick?

    Thanks,
    Helmut
     
  14. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    #14 Helmut, Mar 26, 2010
    Last edited by a moderator: Sep 7, 2017
    How about on this diagram? Its for a 78 GTS. It doesn't show any pressure regulation outlet.

    It also shows one less hose/valve at the fuel pump. Any thoughts?
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  15. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
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    I believe the early car have a vented gas cap. All of the emission stuff was removed from my car when I got it. Nothing on it. My gas cap is vented so I do not get any pressure build up in the tanks. Also the small tubes on my passenger side tank are plugged off. There is also a vent tube on the filler neck. The only down side is that after you park the car you get gas vapors/smell out of the air cleaner duct on the passenger side. The vent lines on the carbs are also plugged.
     
  16. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    I didn't know about the vented gas caps, but it sounds like a good idea to me as I would rather have the fumes come out the gas cap rather than somewhere in the engine compartment.

    Thanks,
    Helmut
     
  17. flyngti

    flyngti Formula 3

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    #17 flyngti, Mar 26, 2010
    Last edited by a moderator: Sep 7, 2017
    That is the TAV12 diagram, which is just the fuel system part. TAV11 is the eval system.
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  18. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    That's for a euro version 1978 308B/S -- uses a vented gas cap as Steve King mentioned.
     
  19. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    What would you guys recommend.... connecting Unit B back into the system or simply using a vented gas cap?

    Thanks,
    Helmut
     
  20. flyngti

    flyngti Formula 3

    Jul 16, 2009
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    On my US 78 308 GTS, I have the three small lines from the right tank going to the liquid/vapor separator can and a line running from the top of the can venting to the atmosphere (no carbon can). I believe I have the original non-vented cap. The times where I have opened the filler cap after stopping the engine, I have heard a release of pressure, but no more than I've experienced with any other car.
     
  21. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    I think in order not to get the vapors out the air cleaner duct, there is a somewhat complicated flap and pump system. There is a flap inside the airfilter housing which has several functions, one of them is to close after you shut off the engine and then a pump supposedly sucks the vapors out. That flap also regulates how much cold air gets into the engine at start up I think.
    On my 78 that flap was stuck open and the suction system wasn't working anymore, so I removed it all as it is too much of a hassle to rebuild it.


    Thanks,
    Helmut
     
  22. Helmut

    Helmut Formula Junior

    Dec 11, 2004
    640
    I would assume that your car also had the charcoal canister at one point but somebody removed it.
    What happened to the vent outlets on the intake manifold under the carbs? They must be plugged, I would think.

    Helmut
     
  23. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
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    I capped the carb runner vent lines. I may resurrect them in the future if I go EFI and use the cumulative reading for a MAP sensor and see if it works.

    My car never had that stupid flap and pump thing, as the car was originally destined for the Euro market,and diverted to the NA market. There are provisions for it, but it was never installed/made operable. I believe the flap was fixed in the closed position, from memory.

    Doug
     
  24. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
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    No flap in a 77 air cleaner.
     
  25. flyngti

    flyngti Formula 3

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    Yep, can was removed and the other lines plugged. The air cleaner flap was jammed open.
     

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