Date:         Mon, 1 Nov 1999 14:26:34 -0500
Reply-To:     David Beierl <dbeierl@IBM.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@IBM.NET>
Subject:      Re: Digifant, barometers, and the AFM
Comments: To: daveb@CP.NET
In-Reply-To:  <381DE41E.F352FE2E@cp.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed

Er... from Chapter 3 page 7 of the Bosch FI book, detailing limitations of
the vane-type AFM sensor..."Second, the sensor vane measures volume of air
intake, but the engine burns weight, or mass of air.  Colder air is heavier
and requires more fuel than the same volume of warm air.  The air
temperature sensor corrects for this problem to some degree..."

And from Chapter 3 page 23 "...It is also known as the hot-wire
sensor...several advantages over the vane-type...1) It measures air mass,
or weight, so it requires no correction for changes in density due to
temperature or altitude..."

 From my reading of the Bosch book, the only altitude compensation in
either Digijet (L-Jetronic) or Digifant 1 is provided by the O2 sensor.

david

At 14:03 11/1/99 , Dave Bayer wrote:
>         As someone recently said, the air density is taken into account
>by the AFM. It is an air MASS detector - the momenteum (mass x velocity)
>of the air is what pushes the vane back, less dense air will push less
>against the vane as said air rushes past to fill the low pressure spot
>in the intake manifold... The Probst Bosch FI book details it nicely
>and is a very good read for anyone who wants to know how their FI
>system works.

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