Date:         Thu, 5 Sep 2002 11:31:03 -0500
Reply-To:     Grungy <grungy@MINDLESS.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Grungy <grungy@MINDLESS.COM>
Subject:      Followup: sucking gas tank...
Content-Type: text/plain; charset="us-ascii" ; format="flowed"

Several responses to my question - I've posted excerpts below.
However, there are varying opinions on where make-up air is supposed
to enter the gas tank.

I personally like the idea of a clogged vented gas cap, but I don't
think the gas cap is vented.  I have removed and disassembled the gas
cap (251 201 553) and can find no evidence of a vent, much less a way
to clean it out.  I removed everything on the "inside" of the cap -
the pin that retains the red guide, the locking tab part, seals and
spring.  This leaves a black plastic part with the lock cylinder
still inside.  No idea how to remove the lock cylinder.  There is an
o-ring that seals the rotating part from the fuel side of things, but
I can't see how to get the rotating part out - there are no other
obvious fasteners.  There may be some special place to drill it out,
but I can't find it.  There also does not appear to be anything like
a hole or orifice that could allow air to pass in from outside.

I remember checking out a new gas cap at the dealer at one time, and
discovered that it was virtually identical to the one that I had and
saw no need to pay for a repeat of the problem.

Four of the vent lines on the tank go to the expansion tanks - two
from the left and right rear metal vent tubes and two from the
crossover tubes on the top.

The lines coming off the top of the expansion tanks combine at a "T"
fitting, and the other leg of the "T" goes back to the charcoal
cannister.

Staring at the ETKA pages that Gary sent me, it looks like there are
three lines on the charcoal cannister (there are).  One is the vent
line to the expansions tanks.  Another is a larger diameter hose from
the top of the cannister that goes to the check valve.  The other is
a large diameter hose that comes off the bottom of the cannister and
goes to what looks like the air cleaner housing.

As I read this - all of these tubes are sources of suction, not relief.
Which one do I have wrong?

It does look like I need to do a diagnosis of function on the
three-tube check valve.  Everything else in the system looks like it
just sits there and carries air (or fumes) in one direction or
another.  The check valve is the only multi-state device that could
fail without looking any different.

I know that the small tube from the top of the charcoal cannister is
clear - I connected an aquarium pump to it to pressurize the fuel
system to look for leaks after reinstalling the tank, and it
proceeded to spew residual gasoline out of the fuel-pump side fuel
line port (which was disconnected at the time).  I was going to put
my thumb over the tube to check for pressure buildup, but the steady
stream of gas answered that question - it was sealed tight.

Of course my '90 looks quite different from the photograph in Bentley.
That shows the check valve in the engine compartment behind (in front
of) the air filter.  Mine is underneath, quite close to the charcoal
cannister.

I can't nail down which lines are 1,2,3 or 4 with any certainty, to
start pulling them off to suck on them to check the check valve.

Logically, with the EPA in mind, there are two sources of suction -
one is the gas tank itself as fuel is removed.  The other is the air
intake system.  The check valve allows air to flow through it, but
only when a vacuum is applied to the third line.

How do I figure out which line is which, going through the firewall?

How do I check the charcoal cannister to see if it is "clogged"?

At 12:24 AM -0500 9/5/2002, Joel Walker wrote:
>   > Anyone know what causes the excessive suction?
>>   Are there other valves that allow replacement air to
>enter the
>>   system?  Something should make up for the suction
>through the vent
>>   lines and the charcoal cannister.
>
>yup. check the line to the charcoal cannister. and the
>cannister itself might be clogged up. that's the vacuum
>relief route.
>
>>   What do the two "gravity valves" on the tops of the
>expansion tanks
>>   do?  Bentley says that they should activate when
>turned 180 degrees.
>>   That seems odd, as the only other time that that
>valve would
>>   experiece such a reversal would be roof down::wheels
>up.
>
>yup. they are designed to stop the flow of gasoline out
>of the tank if you roll the bus. so the gas doesn't
>drip/run down into the dash, where there are likely to
>be sparky-thingies who want to go boom in the night. ;)

I concur - these are a good thing to have, and I hope never to need them.

At 5:17 AM -0700 9/5/2002, Timothy Hannink wrote:
>Its possible that the lines connecting the valves to
>the charcoal canister are pinched. Mine were almost
>pinched closed between the top of the expansion tank
>and the fenderwell. Drop the expansion tanks and check
>the valves and hoses.

At 9:38 AM -0400 9/5/2002, SStones wrote:
>
>At 11:54 PM 9/4/02 -0500, you wrote:
>>Anyone know what causes the excessive suction?
>
>Your gas cap should leak in air when the vacuum inside the tank gets
>to a point long before the tank starts to distort...  See if you can
>find the part of the cap that should bleed air inward on external
>pressure and clean that up so it operates properly...
>
>>Could a faulty check-valve on the vacuum line between the engine and
>>the charcoal filter cause this?  It's about the one thing that I
>>haven't messed with.
>
>Not really...  If that's stuck closed, your charcoal filter would
>just never get dried...  If it's stuck open your gas cap relief
>should still let the air into the tank...
>
>In my mind, the problem is with your gas cap.  Clean it up and
>hopefully that'll be all you need.
>On the plus side, it means that the gasket on it is in great shape.

At 8:13 AM -0700 9/5/2002, gary hradek wrote:
>    If I were addressing your problem I would
>selectively disconnect items to find the cause.
>Pictures should help.   My best guess is that the
>elaborate system is designed to compesate for filling
>problems and emmision problems.   Yours is not a
>filling problem.   Look for your emmision problem.


--

bcnu - Grungy  (Houston, TX)
'60 dddPanel '69 Bug '90 Vanagon '93 Eurovan '00 Audi A6 Avant
grungy@mindless.com           opinions are just that.obviously.
--

bcnu - Grungy  (Houston, TX)
'60 dddPanel '69 Bug '90 Vanagon '93 Eurovan '00 Audi A6 Avant
grungy@mindless.com           opinions are just that.obviously.