Date:         Thu, 11 Mar 2004 19:51:14 -0800
Reply-To:     TinkerMan <tinkerman007@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         TinkerMan <tinkerman007@YAHOO.COM>
Subject:      # AFM problem analysis...
Content-Type: text/plain; charset=us-ascii

Hello again, Volks...

I seem to have the AFM related motor hesitation
problem, where once in a while the motor "hiccups" and
turns off. I can usually restart without problems.

I think it's about time that I find out if indeed it's
a faulty AFM.
Of course there's the option of building Darrell
Bohler's Digitool for conveniently analyzing the ECU
signals including AFM output, but I just don't want to
touch the ECU (for connecting the internal flat cable)
because mistakes happen and I don't have a spare...

So I want to be able to test the AFM without even
opening it (as opposed to some suggestions I saw),
without even moving the van. As far as I understand,
the problem arises from the abrasion of the resistive
element inside by the moving wiper, causing erratic
contact and hence weird voltages (not related to
actual airflow) are generated and make the ECU go
wild...
Here's my idea: connect an adjustable vacuum source
(e.g. vacuum cleaner with adjustable electronic speed
control) and connect it to the AFM output port (going
to the motor air inlet manifold).
Also, connect a small battery to the two ends of the
internal variable resistance voltage divider and a
voltmeter to the variable output (because what matters
is the voltage the ECU sees from the voltage divider,
not any specific resistance). These signals are easily
available at the AFM connector, which is very easy to
disconnect from the ECU harness.
And now, turn on the vacuum slowly and watch for a
monotonic rise of measured voltage.
If there are any sudden surges, we found the
problem...
I just wonder what air flow typically flows through
the AFM, so that I can adjust the vacuum not to damage
the delicate AFM mechanics.

SOOOOO...what do you think about this idea, volks?
I'm planning to implement it real soon...

cheers, T-man

=====
Cheers, T-man.

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