Date:         Thu, 2 Aug 2001 20:47:46 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Fuel Pressure Info
Comments: To: Mark Ingalls <ingalls_mark@HOTMAIL.COM>
In-Reply-To:  <F141aZWZaendgjvM9Kf0000dc1e@hotmail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 07:46 PM 8/2/2001, Mark Ingalls wrote:

>But I have 38#'s with the vacuum hose disconnected, where the back of
>Bentley calls for 35#'s.

I can't find anything on the back -- Bentley 24.25 and 24.55 say 2.5 bar /
36 psi.


>That matches the 3# difference I had with the vac hose connected, without
>the fancy math.

Mark, there's no fancy math.  The regulator exists to maintain a 36 psi
difference between the fuel rail and the inside of the intake
manifold.  That's the full extent of its job.  I don't know what tolerances
Bosch considers acceptable.

What makes it look more complicated is thinking about manifold pressure in
inches of vacuum, instead of in psi (absolute).  Once you start thinking
about what's *in* the manifold instead of what *got taken out* then the
fuel regulator becomes very easy.

You could measure this value directly by putting the fuel-pressure gauge in
an airtight box and connecting the inside of the box to the inside of the
manifold.  Then the gauge should read 36 psi no matter what the engine was
doing, and you could see very directly how well the regulator was doing its
job by seeing how far it was from 36 psi at any given moment.

cheers
david


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