Date:         Sat, 4 Nov 2006 10:40:04 -0800
Reply-To:     jon <jon@KENNEKE.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         jon <jon@KENNEKE.COM>
Subject:      Re: AFM Voltage Ratios
Comments: To: Geza Polony <gezapolony@SBCGLOBAL.NET>
In-Reply-To:  <vanagon%2006110413151141@GERRY.VANAGON.COM>
Content-Type: TEXT/PLAIN; charset=US-ASCII

One way to figure this out is to connect a MAP to the engine with a known
good AFM. Then, compare the values. Since it appears AFMs are linear, and
so are MAPs (at least the ones I looked at), a circuit could adjust a MAP
output to simulate an AFM.

Jon

On Sat, 4 Nov 2006, Geza Polony wrote:

> This is a question I've been asking for a long time, both here and on
> westfalia.org, and no one seems to know. You're right, there must be SOME
> concrete relationship between manifold pressure and AFM output voltage, but
> no one seems to know what it is. The Bentley doesn't help, either. I took
> mine off and measured the voltage using a hair dryer to simulate the air
> flow, but that doesn't really tell you anything except that the voltage does
> change, and pretty much evenly.
>
> Without knowing what the voltage should be for a given set of AFM
> conditions, it's impossible to calibrate the AFM. And you can bet that, with
> most of these AFM's having 20-odd years on them, the voltage output "ain't
> what it used to be." That would mean that at some point in the scale of air
> flow, the engines are running too rich or too lean.
>
> Unless there's something we're not getting. Why wouldn't the voltage data be
> available?
>
> ??
>
> Geza
>
> On Fri, 3 Nov 2006 18:22:51 -0800, jon <jon@KENNEKE.COM> wrote:
>
> >Does anyone have data on AFM voltage (out of the resistive divider) versus
> >manifold pressure? I would think they would directly correlate in some
> >linear fashion.
> >
> >Yes, I think of these types of things on a Friday night. ;)
> >
> >Jon
>