Date:         Thu, 10 May 2001 12:49:00 -0400
Reply-To:     David Beierl <dbeierl@attglobal.net>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@attglobal.net>
Subject:      Re: Gas Milage and the Fuel Pressure Regulator
Comments: To: Mark Keller <kelphoto@islandnet.com>
In-Reply-To:  <3AFACF83.6F99F15B@islandnet.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Mark, thanks for a superb post.  One item though:
At 01:28 PM 5/10/2001, Mark Keller wrote:
>Also, I've mentioned in the past, but it's worth restating.  The vacuum
>produced by the engine also affects fuel regulator pressure, because the
>strength of the vacuum is what keeps the fuel pressure LOW. When an
>engine is worn, has vacuum leaks, poor timing and etc., the vacuum
>created is below the needed amount.  This translates into the fuel
>pressure regulator setting a higher fuel pressure. High fuel pressure is

This is wrong.  The whole purpose of the fuel regulator is to maintain a
constant pressure *relative to the manifold pressure* and that is what it
does.  The quoted range 29-36 psi should really be quoted as 2.5 bar (36.75
psi) over manifold pressure.  If you're measuring it with a normal gauge
that is referenced to ambient pressure, you'll see the reading drop when
the engine is running -- but if you use a gauge that can be referenced to
the manifold (or enclose a regular gauge in a box that is connected to
manifold pressure, which is the same thing) you will see a constant reading
as the engine starts, runs, throttles up and down etc.

Because the injectors are exposed to fuel pressure on one end and manifold
pressure on the other, the fuel regulator maintains a constant pressure
drop across them and therefore a constant flow rate regardless of engine
conditions.

david


David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"