Date: Mon, 3 Mar 2008 23:41:41 -0500
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Calif 2008 emissions fuel tank pressure testing?
In-Reply-To: <0ac601c87dad$2c21b580$0a00a8c0@OWNERMIKE>
Content-Type: text/plain; charset="us-ascii"
Gasoline naturally wants to make pressure-vapor pressure. Add a little
heat and some agitation and it will vaporize quickly. As I said, when the
engine is not running and when at idle, the system should be closed. As
soon as the throttle goes off idle, the control valve should open and the
tank can then get air as needed to make up for the fuel being consumed. If
the system is leak free and the valve does not open the pump will hove no
problem collapsing the tank. Clogged carbon canisters can make a real
mess. In particular, those aftermarket tanks collapse with little effort
at all. OBDII vehicles actually sense this vapor pressure and if not
reached in some predetermined time a fault code will be set. Yes, a loose
or defective gas cap will set a fault.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Mike
Sent: Monday, March 03, 2008 11:07 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Calif 2008 emissions fuel tank pressure testing?
If it was truly a completely 100% sealed-tight fuel system, it would "run
out of fuel" after using a small amount, due to the vacuum created by the
feul pump sucking fuel out of the sealed tank. If no air can go in, then
no
liquid will be able to come out after a little is consumed. IIRC, there's
a
problem who's symptom is that you when you remove the filler cap, there's
a
lot of vacuum released that was causing fuel starvation; bad check valve
or
something?
Mike B.
----- Original Message -----
From: "Dennis Haynes" <d23haynes57@HOTMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, March 03, 2008 9:19 PM
Subject: Re: Calif 2008 emissions fuel tank pressure testing?
> When the engine is not running, or at idle, the tank should be sealed.
> Fumes are collected in the carbon canister but should not be released to
> the atmosphere. When the engine is off idle, the valve for the carbon
> canister should open and the fumes vented into the air filter and burned
> off in the engine. As fuel is sucked down, replacement air should also
be
> drawn in through this valve. You should be able to hear the valve click
> open when the throttle is opened. One of the problems with most engine
> conversions is that the throttles are not ported to properly operate
this
> valve.
>
> Personally, I do not think it is unreasonable for the fuel system to
> remain tight and prevent evaporating fuel from just venting into the
air.
> By 1971 almost all cars had some type of vapor recovery system. If this
> test finds leaky systems that need to be fixed, then it is serving the
> intended purpose even if the program is not perfect.
>
> When the tank is filled, it not vented through the carbon canister. The
> actual vent is through the filler and the vapor recovery nozzles are
> supposed to collect those fumes and bring them back to the stations
tank.
>
> Dennis.
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of
> John Bange
> Sent: Monday, March 03, 2008 8:54 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Calif 2008 emissions fuel tank pressure testing?
>
>> Maybe I'm operating under the wrong misconception, but I don't
> understand
>> how a tank can be expected to hold pressure when it presumably vents
> thru
>> the charcoal canister to let the air out while being filled. Can
> someone
>> explain?
>>
>
> Yeah, you got me. The guy at the test place didn't explain it very
> thoroughly, plus I wasn't listening very well. All I know is it involves
> pressurization (vacuum?) of some sort, and takes 15-20 minutes to test.
> Perhaps a charcoal evap filter only should be able to pass a certain
> volume
> of air in a given time, and if too much can pass, that indicates a leak?
>
> --
> John Bange
> '90 Vanagon - "Geldsauger"
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