1978 308 evaporative emission's valve | FerrariChat
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1978 308 evaporative emission's valve

Discussion in 'Technical Q&A' started by Beta Scorpion, Sep 18, 2006.

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  1. Beta Scorpion

    Beta Scorpion Formula 3

    Jun 22, 2006
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    #1 Beta Scorpion, Sep 18, 2006
    Last edited by a moderator: Sep 7, 2017
    The routing and function of the evaporative system on a USA 78,79,80 carb. 308 has been causing sleepless nights for myself.

    The earlier system had a very easy to understand 3-way valve to control the vapor from the fuel tank. The later system went to a 1-way (or 2-way) valve that has me a little puzzled. When the valve is installed so that the flow of fumes can only go from fuel tank to charcoal canister the potential for a vapor lock in the fuel tank exists.

    When the valve is turned around to prevent vapor lock in the fuel tank, NO fumes can get into the charcoal canister.

    Perhaps these cars are supposed to have a vented gas cap?

    The following is from a history of evaporative emissions at: http://web.bsu.edu/tti/5_1/5_1e/5_1e.htm
    "One major source of HC emissions in both systems is fuel tank venting. During the course of a day, the tank heats and cools, causing pressure variations. As fuel expands and evaporates in the heat of the day, it builds a positive pressure. The fuel system must be vented to prevent components in the fuel system from leaking as a result of system pressures becoming too high. And as the fuel is consumed, air must be allowed to enter the tank to prevent the collapse of the tank resulting from the lowered internal pressure. One component that has been added to the fuel system is a vented fuel cap. These caps are designed to allow air to enter the tank during a period of low pressure, or vacuum, while resisting the release of air containing HC during times of high pressure. Pressurized air/HC in the system still needed somewhere to go. The charcoal canister was the answer. The reason charcoal was chosen as the storage medium was for its vast surface area and its ability to adsorb the excess vapors in the fuel system."

    However, the 78 308 gtb owner's manual clearly states "Sealed [gas] Cap."

    Another explanation may be that there is some additional valving mechanism in the small air pump when it is not pumping.

    Or perhaps, in real life settings, the volatility of gas and the rate of consumption never reach a point where there would be a vacuum in the fuel tank.

    Or my valve is malfunctioning and there is some way pressure in the "anti-" direction will cause vapor to go through (mine clearly is one-way, no matter how hard I blow in the anti- direction) the 78 308 owner's manual describes it as a "two-way valve."

    Does anyone know of any official documentation of this system that demonstrates its functionality (other than the 78 308 owner's manual). The 308 Shop manual does not describe this later system and the tech. bulletins I have seen do not describe it.
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  2. Beta Scorpion

    Beta Scorpion Formula 3

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    #2 Beta Scorpion, Sep 19, 2006
    Its not that I am so concerned with killing trees and animals with evaporative emissions, but this system is intimately related to the fuel system, and with the predisposition of these mid-engine cars to ignite, I believe diligence in keeping this evaporative system working correctly is essential.

    Every time a post about fixing up the old 308s occurs someone always chimes in with the need to replace all the hoses and fuel lines. But what about these evaporative lines? They are just as important.

    If one just throws this system in the trash and caps off everything you are still left with a vent hose coming out of the gas tank that has to go somewhere and has the potential to distribute flammable fumes to the engine compartment.

    I also wondered about the physics of the ‘air pump’ that scavenges fumes from the air box. Where are these fumes going? The volume of air in the air box is perhaps 4 liters. Where, in the closed evaporative system, can 4 liters be housed? The air has to be recycling through the system and exiting into the intake manifold while the scavenger air pump is pumping.

    My intent is to defeat the scavenger air pump (it no longer works anyway) by tapping a grub screw in the nipple connector to seal it. That way I can still hook a ‘non working’ hose to it for a correct functional appearance and maintain integrity of the rest of the system. (My scavenger circuit allowed charcoal particles into the carbs and really fouled them up).

    The problem with the little caps for ‘capping off’ these devices is that with the rubber cap in place one cannot hook up a ‘correct-looking’ hose for concourse appearance.

    Again, with the vacuum system, I am going to insert a grub screw into the first ‘T’ connector to seal it off. That way any leaks down stream will be irrelevant and I can hook up all those vacuum hoses where they are supposed to go and not have to worry about little air leaks at all the other ‘T’ connectors and the two electrovalves.

    I thought the grub screws would be a good idea because they are not permanent, they would be hidden and the likelihood of down-stream emobilization would be low.
     
  3. Peter

    Peter F1 Veteran
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    #3 Peter, Sep 19, 2006
    Last edited by a moderator: Sep 7, 2017
    I've tried through the various parts stores/suppliers up here in Canada and none of them carry my earlier three-way valve, but fortunately, mine still works. Looking at your diagram, I don't see why an earlier three-way valve would not work, as really, the only difference is that under excessive gas tank pressure, it is released into the atmosphere (your later system is completely sealed, thus not allowing any excess pressure to dump into the atmosphere. I can't figure how that is handled in your system...). Otherwise, normal pressures in the tank are released into the carbon canister and if there is a lower pressure in the gas tank, atmosphere is drawn into the system via that valve (intake is an opening in the mounting flange).

    If you can find someone that sells that three-way valve, let me know (I'll keep one as a spare if my original fails).

    Your proposal sounds good and even as far as copying the earlier (my) system if you can find that valve would work. My air box has no flaps or other gizmos and fumes from the carbs just evaporate through the intake (giving the garage a nice aroma ;) ).

    I spliced a generic fuel filter inline along the hose to prevent those carbon bits from plugging up the ports. Sorry not concours, but functional.
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  4. Irishman

    Irishman F1 Rookie

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    #4 Irishman, Sep 20, 2006
    Damn! Does the rest of your engine look that good? Also, what kind of coolant hose is that? I need something more supple than the NAPA hose I found -- in some spots it was really tough to install.

    Thanks,
    Seamus
     
  5. Beta Scorpion

    Beta Scorpion Formula 3

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    #5 Beta Scorpion, Sep 27, 2006
    Now I am really upset about not being able to really figure this system. I was just poking around with a vacuum tester and it looks like that pipe that comes out of the bottom of the charcoal cannister is a free passage back and forth to the atmosphere. So when the car is shut down, the little air pump blows the fumes through the charcoal cannister and out the bottom of the cannister onto the hot header! It just does not seem safe that the one place the system is open to the atmosphere is right over the header.

    It also means that while the engine is running, 6 cylinders are sucking a small amount of air constantly through the metered orifices (coming in through the pipe, open to air, at the bottom of the charcoal cannister) while 2 of the cylinders feed into the vacuum system and should not be continuously sucking unless there is a vacuum leak.

    Can this be right?
     
  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #6 Steve Magnusson, Sep 27, 2006
    Last edited by a moderator: Sep 7, 2017
    I believe it's not sealed in the sense the there is no airflow at all to the outside world, but rather in the sense that any air+fuel vapors must pass thru the charcoal element before reaching the outside world (i.e., no fuel vapors get out).

    I had the same concern that the 6 little tubes supplying the fuel evaporation system were "open", yet the remaining 2 little tubes on cyl 3 & 4 running the air injection diverter valve were "closed". I wrote FNA about it, and Mr. McCay wrote back that it really wasn't enough to worry about; however, I measured it, and it was about 0.5 Kg/hr at 1000 RPM idle so I modified the system per the attached diagram to have all 8 little tubes evacuating the charcaol canister and connected the air injection diverter valve stuff to the "closed" vacuum system running the airbox flap mechanism. This causes the air diverter valve to "dump" the air injection air out to atmosphere always at 4400 RPM; whereas, in the stock arrangement, the air injection air would only be dumped at 4400 RPM and a high vacuum condition (which isn't a big deal IMO):
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  7. Beta Scorpion

    Beta Scorpion Formula 3

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    #7 Beta Scorpion, Sep 28, 2006

    Wow, Steve, thanks for the post and diagram. I was hoping someone had questioned this before.

    One of my concerns is that charcoal may have plugged some of the meetering orifices in the intake manifold and I was thinking of some way to cap them off and have the EVAP system discharge somewhere else.

    My concern was raised when I rebuilt all the carbs and set all 8 idle mixture screws the same number of turns out. Spark plug cuts at idle demonstrated vastly different mixtures from all black electrode to all white electrode. I used the mixture screws to even out the color of the plugs (I'll save this 'idle plug cut' method of setting idle mixture for another thread).

    Anyway I wondered what if the TOP of the charcoal cannister was routed to the fixture under the airbox so the fumes went into the airbox and all the manifold fittings were plugged. The middle charcoal cannister outlet would be plugged (or have a 'faux' route to the little air pump for concourse purposes).
    The fitting below the charcoal cannister would accept the fumes from the tanks in the standard manner.

    I wanted to do some research to see if any other cars of that vintage routed the EVAP fumes to the airbox rather then right into the intake. Perhaps this type of hookup will cause it to explode if there is a backfire?
     
  8. BigTex

    BigTex Seven Time F1 World Champ
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    #8 BigTex, Sep 28, 2006
    I have seen a sectional of the charcoal canister..it DOES allow escape to atmosphere and I suppose if functioning the fumes are stripped of flammable HCs..I wonder after all this time if it's not saturated....

    Sadly most of this stuff was gone from my 1977..and they FORGOT to plug a vacuum line to one of the components! LOL!

    Once we plugged that the car ran MUCH better.

    Truthfully, once the flap in the airbox is defeated and open all the time, the carb box vents back out the RH scoop, and the tank vents go thru the charcoal can...

    That's my real world answer, and the water heater is NOT in our garage....

    It's just not that much HC in the carb box although I guess over time the expansion fumes of the tanks would accumulate in a totally closed garage...
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #9 Steve Magnusson, Sep 28, 2006
    I can't comment too directly because I don't really know what's inside the '78-'79 308 charcoal canister (e.g., did they put some of that early separate 3-way valve functionality inside the canister itself?), but I really don't see what "problem" you are trying to address (compared to just hooking it up how it should be -- except using all 8 little tubes to the top fitting). Some concerns:

    1. With the stock connections, the top fitting is always at a lower pressure than the middle fitting when the engine is running (when the little air pump isn't running, it just looks like a thru tube connection -- no valving inside).

    2. I don't think you can just plug the middle fitting as this may be the source for clean filtered air under the conditions where air needs to be drawn into the fuel system.

    If you can get more details on what's really inside the charcoal canister, I'd be glad to look it over, but otherwise, I've got no information.
     
  10. Beta Scorpion

    Beta Scorpion Formula 3

    Jun 22, 2006
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    #10 Beta Scorpion, Sep 28, 2006
    Thank you for you thoughts. To clarify, I am worried that the EVAP system is messing with my idle mixture to a different degree in each cylinder & curious as to why all cylinders would not have the same mixture at idle if the mixture screws were all at the same # of turns out. So, as a test I wanted to see if the idle mixture would be the same in all cylinders if all 8 tubes were plugged (and drive the car around without it blowing up).

    This would let me know if there is a leak in one of the hose connections or 'T' connectors that I need to track down or if any of the passageways to the intake manifold are plugged that may need some major dissasembly to clean.

    I really want to hook it up the way it should be and
    I do not mind if the two cylinders hooked to the vacuum sytem are different as this may be expected. I just want to track down the reason why the other 6 cylinders all need a different idle screw mixture setting. (of course this may 1. not be a problem at all or 2. may not be related to the EVAP system at all)

    By blowing into hoses connected to the charcoal cannister it does not seem to have any valving mechanism to any of the openings. Flow through the device is probably all related to differential pressure and changes vapor density due to heating.
     
  11. bill308

    bill308 Formula 3
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    #11 bill308, Sep 29, 2006
    Just to add a little more information here, the tubing from the charcoal canister feeds fuel vapor and air to small drilled holes in the intake manifold. These holes are much smaller than the id of the feeding tube, but at idle have a significant effect on rpm. If I block off these feeds, idle speed drops noticably.

    I've had correspondance with Steve in the past concerning this system and adopted his plumbing arrangement. In my case, I fitted hose barbs to all eight intake throats to enable fitment of a multi bank manometer system to facilitate air flow balancing and when not in use for this purpose, provide equal distribution of vapors from the fuel canister using soft tubing. I used soft tubing lengths of equal length to effect a 1-to-2, then 2-to-4, and finally a 4-to-8 piece arrangement to achieve near equal balance for the vapor circuit. The (single) 3-way valve signal was plumbed to the number-8 cylinder vacuum tap, upstream from the vacuum storage sphere one-way valve. With the new carbs I fitted a couple of years ago, I find the mixture settings at idle, are pretty close turn wise, probably within about +/- 1/2 turn.

    Bill

    Bill
     
  12. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #12 Steve Magnusson, Oct 3, 2006
    Beta -- Another thread reminded me of something that might be causing your problem of the mixture screw openings not being very similar and that's if the choke spool valve inside the carb is not sealing well when it's supposed to be "closed". Even if the exterior linkage seems OK, the spool itself may be stuck open, or the sealing surfaces of the spool and or seat might be pitted/corroded -- just a thought...
     
  13. Beta Scorpion

    Beta Scorpion Formula 3

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    #13 Beta Scorpion, Jan 11, 2007
    Just a followup post. First, the diagram I made for the first post on this thread shows no air going into the bottom of the charocal cannister, this is incorrect, as air enters easily through that opening and feeds through 3 of the 4 carbs.

    I got my vapor system hooked up like the original and my car runs great now.

    One additional thought on the carb that recieves no vapor from the charcoal cannister: There was a Fiat 1600cc spider that had twin Weber carbs. One of the carbs accepted a feed from the charcoal cannister and the other carb DID NOT. One way to even things out in this system was/is to open the bypass screws 1 to 1.5 turns on the carb WITHOUT the vapor feed. So, in an analagous manner, the air bypass screws on the Ferrari 308 carb without the vapor feed could be opened 1 to 1.5 turns. I may do this on my car the next time I set the synchronization, just so I can sleep better at night knowing everything is going to be even and I can keep the factory original hose routing.
     
  14. rjd2

    rjd2 Karting

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    #14 rjd2, Jun 2, 2023
    Hi all-my 1978 US spec carbed GTS is running fantastically-new fuel lines, coated tanks, etc. however, the charcoal canister came up missing in my engine rebuild. i now get some fuel spillover if i fill the tanks to full. i looked over these diagrams, and i bought a charcoal canister, but have a few questions:

    1-i know that the charcoal can disintegrate, and clog carbs. is there a way to test the status of the canister?
    2-the valve between the tanks and the canister; what does that look like? i do not know where it would be mounted, if it's still in the engine bay.

    thanks for the help; i'm less concerned about preventing any evaporation to the atmosphere, as i am about safety and fuel spillover.
     
  15. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #15 Steve Magnusson, Jun 2, 2023
    Last edited: Jun 2, 2023
    For 2 -- Post #1 in this thread has a picture of that valve and it's mounting location on the rear wall of the engine bay:

    https://www.ferrarichat.com/forum/threads/what-is-this-hose-1979-308-gts-usa-carb-model.677908

    See also the figure in the 150/78 OM:

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  16. rjd2

    rjd2 Karting

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    #16 rjd2, Jun 3, 2023
    Thanks Steve. well, it looks like this valve came up missing when my car was being restored.

    i'm not so concerned with feeding the fuel vapor back to the carb/intake system, however, i do need a way to prevent the fuel vapor from overflowing at the passenger side fuel tank. can i vent the gas tank to the charcoal canister, and the canister to atmosphere via a tube to the rear? concourse judges are not high on my priority list FYI. thanks!
     
  17. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #17 Steve Magnusson, Jun 3, 2023
    I think there is a very good chance that other US cars of the same era use a similar two-way valve -- but that's your homework ;). Here's an example that isn't quite the right form factor:

    https://www.ebay.com/itm/164831044845?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=164831044845&targetid=4580359295528871&device=c&mktype=&googleloc=&poi=&campaignid=437225724&mkgroupid=1228154759183859&rlsatarget=pla-4580359295528871&abcId=9300907&merchantid=51291&msclkid=00c169b944c21e52b5d80dc2bec5d99c

    If you can't find an appropriate two-way valve, just hook it up like the OM figure and leave the two-way valve out of that hose (but have the hose). I believe the function of that two-way valve is to allow the tanks to slightly pressurize so that the carbon bed in the charcoal canister doesn't get saturated (and become ineffective) too often -- i.e., that valve only allows fuel vapors to exit the tanks when the pressure in the tanks is a slight positive pressure (not at zero pressure). In any case, having fuel vapors come out of the hot air purge tube, G, would be better than having it come out near the passenger window. Do you have the rest of the system, like D, in place?
     
  18. rjd2

    rjd2 Karting

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    #18 rjd2, Jun 4, 2023
    Thanks Steve. I'm having a hard time visually assessing whether the "D" portion of the diagram is in place, since it's so tightly tucked underneath the passenger side "shelf". As best I can tell, there is a cluster of 3 nipples that exit the PS tank, with fuel hoses connecting to an assembly of 3 metal hoses, these entering the underside of that shelf. I may need to use a little USB camera to see what's happening under there. the symptom I experienced is when filling the car fully with fuel, i got some spillover of fuel that ran down the PS tank. If "D" should be mounted on the firewall side of the engine bay, then I do not see it in place. I'll poke around down there with a USB camera and get a better idea of what's happening. appreciate the help!
     
  19. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #19 Steve Magnusson, Jun 4, 2023
    Last edited: Jun 4, 2023
    Yes, it's best to remove the RH rear wheel and fender liner to mess about with D. The question is what is connected to the top of D (if there). Also, those three little hoses only get "wetted" when the tank is near full = they can be cracked and not show an obvious problem when stationary, but be letting out liquid fuel when it's near full and the liquid fuel is sloshing around.
     
  20. rjd2

    rjd2 Karting

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    #20 rjd2, Jun 5, 2023
    Ahh, gotcha. thanks!
     

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