Date:         Wed, 2 Jul 2014 19:41:09 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: AFM test readings
Comments: To: Harold Teer <teer.vanagon@GMAIL.COM>
In-Reply-To:  <CAGwfHKTWmPNUxoqDamwo7cAeG+nn6hfsrP9KTTVZ2+JtFMi9JA@mail.g
              mail.com>
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At 04:30 PM 7/2/2014, Harold Teer wrote:
>My question concerns the measurement between terminals 2 & 3  --- Bentley
>says the value should be a resistance change when the air sensor flap is
>moved

If you measure resistance from either end of the pot to the wiper, it
will vary in seemingly arbitrary fashion when you move the
vane.  Doing that is easy and enough to tell you that it's basically operating.

If you hook the ends up to to ground and plus five volts, though, and
measure voltage from ground to the wiper pin, you should see a smooth
rise from close to zero to close to five volts.  With an oscilloscope
or an analog voltmeter with a lively needle you can detect little
dropouts as you move the vane slowly.  This is because of the special
design of the resistor plate (made by Bourne, a USA company that
builds fancy resistors) which is fed voltage through laser-trimmed
resistors at several points along its length rather than only at the
two ends.  I think the purpose is to allow trimming the response
curve and possibly to make it more resistant to track wear.

You don't need to use five volts if the AFM is disconnected.  Any
voltage from around six down should work fine, with appropriate
adjustments in the expected numbers.  If the AFM is connected to the
system, the five volts is supplied for you by the ECU.

Yours,
David