L-Jet, Air Cleaner valve

[BellePlaine]

Do you see that flat, black disc on the side of the air cleaner? What is its name? What does it do, how does it work, and why is it important?

Not pictured is a hose coming from the charcoal canister to this valve on the air cleaner. So I know that it controls gasoline vapor into the mix of fresh air. But I don't know under which circumstances it allows the vapor to enter or not enter.

[Randy in Maine]

That is the EEC valve and when it opens it allows fuel vapors to be drawn into the air cleaner from the charcoal canister. I think I remeber reading someplace that it opens up about 2000 RPMs or something like that, but I don't know that for a fact. It should be able to hold a vacuum though.

[BellePlaine]

Thanks Randy. Please bear with me, I still have questions.

Do you suppose that the EEC (which I now know stands for "evaporative emission control") valve's first purpose in life is to purge the fuel vapor for the benefit of the gas tank, or is the main purpose to use to increase fuel efficiency? Does it increase fuel efficiency?

Why are the vapors allowed in under high(er) RPMs? Why shouldn't they be let in at idle?

[Amskeptic]

Thanks Randy. Please bear with me, I still have questions.

Do you suppose that the EEC (which I now know stands for "evaporative emission control") valve's first purpose in life is to purge the fuel vapor for the benefit of the gas tank, or is the main purpose to use to increase fuel efficiency? Does it increase fuel efficiency?

Why are the vapors allowed in under high(er) RPMs? Why shouldn't they be let in at idle?

Consider them only as a "problem" for the emissions reducing team at Volkswagenwerk. Fuel tank vapors are just nice big fat HC emissions. VW (and others) discovered that these vapors could dump a pile of unwanted HCs into the engine at inopportune times like hot days at idle, so those rude HC vapors had to be more tightly controlled and released into the engine only when invited, so their contribution would not cause a big FAIL in the emissions regulations. VW was able to allow these rich fuel tank vapors into the intake stream only during part or closed throttle overrun when HCs are normally the lowest, without blowing their certification. Hey! Why not use the vacuum advance signal! OK!
Colin
(p.s. only with advanced electronics in newer cars do fuel tank vapors get utilized for enriching the cold start mixture and performing some transitional enrichment)