Date:         Mon, 25 Aug 2003 13:40:21 +1000
Reply-To:     Stephen Overmyer <s.overmyer@UWS.EDU.AU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Stephen Overmyer <s.overmyer@UWS.EDU.AU>
Subject:      Re: Gas Tank--Thunk!
In-Reply-To:  <200308241834.h7OIYc4s012365@cooper.uws.edu.au>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 02:26 PM 24/08/2003 -0400, you wrote:
>Date:    Sun, 24 Aug 2003 00:32:15 -0400
>From:    Jason Willenbrock <pooncerelli@HOTMAIL.COM>
>Subject: Gas Tank--Thunk!
>
>Hey All,
>Recently on my 90gl the gas tank has been acting wierd.  My inclination is
>in the return lines, but you tell me what you think.  After driving for as
>while and then i come to a stop light, after a few seconds, my gas tank
>goes thunk!  This also happens at the pump.  I begin filling the tank, and
>immediately the thunk occurs as if the tank is expanding.  As far as i can
>tell it does not occur while constant driving, only when stopped or
>filling.  Oh yeah, if I have been driving a while then I shut down the
>van, I wait a few seconds to a minute and behold--THUNK! It is driving me
>crazy.  It is like pressure is being released or not released when it is
>supposed to. What do you all think


   Yes it is annoying...it has happened to me a couple of times in the last
few years.
   What is happening is that air is not getting back to the tank as fuel is
being used
   at the same rate due to a partial blockage in a small tube that leads
via the charcoal
   cannister to the return air line.Most likely culprit is the charcoal
cannister which is
   located up behind your rear right wheel)

   Bits of charcoal eventually get loose and can block the line and it's
not untill
   the pressure difference is so great that air finally gets sucked past
the blockage...
   hence the "thunk sound"...It's no real problem for a while but if
allowed to continue
   ad infinitum,it could eventually lead to a crack occurring in the fuel
tank due to
   metal fatigue.

   To fix the problem (although it may one day come back again) I have
sucessfully
   used the following proceedure...

   Jack up right rear wheel (but no need to remove) to gain better access
to the
   charcoal cannister and remove said cannister (via a large hose clamp)
   Also here is the tube that leads back to the fuel tank which can be checked
   for blockages but I think you will find that getting air to this tube is
the problem,
   not the tube itself.

   There are also two thin tubes (one purple and one white) that lead from a
   connection on the top of the cannister up into the engine bay to the
throttle
   body.Remove these noting which one goes where up at the throttle body.

   Give the cannister a few good shakes to loosen up any lumps or blocks
   and make sure the two small tubes (purple and white) are blown clean
   or insert a thin wire thru them to achieve same result.

   Re-install the cannister and tubes and your problem "should" be gone.

   To be honest,I have never fully been sure which part of the above proceedure
   actually did the trick but the problem is most definatley in this area
   and it's just as easy to clean all parts since you have them out anyway.

   The whole job should only take 10 mins or so....

   Hope this helps,

   Steve O
   NSW Australia
   '92 Transporter WBX Kombi
   '00 Transporter Double Cab
   '03 Transporter Double Cab (work truck)