Date:         Fri, 8 Oct 2004 16:23:51 -0400
Reply-To:     tabe johnson <xtabe@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         tabe johnson <xtabe@YAHOO.COM>
Subject:      Some Fuel Pump Theory
Comments: To: pascal.giasson@GNB.CA
Content-Type: text/plain; charset=us-ascii

Some people may not know this yet, so here ya go:

Our fuel pumps live under the sliding door, just
to the rear of the gas tank.  Some Vanagon models
come with filters before the pump, some with filters
after the pump.  Both filter locations have their
advantages and disadvantages.

The high pressure fuel pumps used on our vans
are great at blowing, but are bad at sucking.  That
is, they can develop >100 PSI of pressure, but can
only suck a small amount of (fuel) vacuum.  In
many other vehicles with similar high pressure pumps,
they use TWO pumps:  The first is a low pressure
transfer pump, which pumps the fuel to the high pressure
pump.  In our vans, VW chose to put the outlet of
the gas tank on its bottom, eliminating the need for a
transfer pump.  I think they did this for packaging and
manufacturing cost reasons.

What this means for us is if you have a fuel filter
before the high pressure fuel pump, you run the
risk of losing fuel flow because the pump isn't
able to suck through thge clogged fuel filter.  On
the other hand, if you have a filter after the high
pressure fuel pump, you run the (minor) risk of
damaging the pump when it tries to pump marbles or
bolts or whatever goodies come in with the unfiltered
gas.

It has been my experience that the high pressure pump
will pump rust, water, and any number of interesting
things and suffer no obvious damage.  Maybe long term
longevity suffers.


--tabe johnson
xtabe@yahoo.com
'87 Westy

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