Could be a matter of the pump design- some pumps draw and prime on their
own, some require some external pressure source (like gravity, for
instance).
In this case, restricting the flow too much through a pre-filter could cause
the pump to starve. I can see (if this was the case) where VW may have put
the smaller single-element filter before the pump to protect it, and put the
larger heavy-duty filter after the pump to take advantage of the pump's
force and trap smaller particles.A change in pump/system design may have
removed or added the need for the smaller filter. I know my van had one and
a PO had removed it. I have a new filter and I'm going to put it back in,
just for GP.

Cya,
Robert

----- Original Message -----
From: "Anonymous Digest" <jbrush@AROS.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, July 05, 2004 9:46 AM
Subject: Re: low fuel pressure and lean engine

> >It so happens that gasoline is very volatile.
>
> You know, I have always suspected that was true <g>
>
> >Most people would prefer the pump breakdown sooner than a sudden vapor
lock on
> >a hot day.
>
> Well, I am not sure that would be the consensus, as one stops you from
going,
> the other stops you from going, and also costs you hundreds of dollars,
but I
> didn't bring it up to be argumentative. It just makes little sense to have
two
> filters in the same line, and as long as you are using a filter, it is
logical
> to put it ahead of the pump and protect it, as well as the rest of the FI
> system.
>
> Judging from what I have read today, Some vans came with a filter in
front, some
> with the filter downstream, and some with both. I respect the VW
designers, but
> it appears that they could simply not make up their minds with regards to
what
> is best, so I guess we are left to our own opinions and logic.
>
> If one has a second filter, it ought to really last a lifetime if there is
the
> smaller one upstream.
>
> Thanks,
>
> John