Date: Sat, 5 Jul 2014 13:27:50 -0700
Reply-To: Neil N <musomuso@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Neil N <musomuso@GMAIL.COM>
Subject: Re: Update on AFM testing procedure
In-Reply-To: <vanagon%2014070516145541@GERRY.VANAGON.COM>
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You know more than I David but with Bosch Motronic 2.9 (and OBD2 as
well), there is an intake air sensor mounted post MAF in intake
plenum.
Mortonic 2.9 ECU uses both IAT sensor and MAF for same or similar
purpose as does the WBX AFM?
I don't know if the "hot wire" in the MAF I'm running gets as hot as
the Platinum part you refer to, but duly noted in terms of cleaning.
There's lots of threads in Mk3 forums re: MAF's getting oil fouled.
Neil.
On 7/5/14, David Beierl <dbeierl@attglobal.net> wrote:
> The one that I read up on long ago would heat the filament to at
> least red hot, possibly white hot for a short time at some point in
> either startup or shutdown cycle, possibly both. Being platinum it
> was much more resistant to that sort of insult than to anything touching
> it.
>
> In use it would maintain the wire at a specific temperature and
> monitor how much current was required at that moment to do so. That
> would allow calculation of how much heat the wire was losing to the
> flowing air and thus what mass of air was contacting the wire in each
> measurement cycle. And finally from that the mass flowing through
> the intake. I think maybe they kept the wire hot enough that
> differences in intake air temperature were swamped - just short of
> glowing tickles the back of my mind somehow. What I'm not sure I
> understood at the time and certainly don't remember now was how they
> measured the temperature of the wire so they could control it. I
> have a bit of a feeling that it was something diabolically clever
> that I thought would have to conflict with what else they were doing
> with the wire,
>
> The wire needs unobstructed airflow (and hence heat transfer) on its
> surface and because it's so thin very small particles on the surface
> can have considerable effect. I think it really has to run squeaky
> clean all the time.
>
> Yrs,
> d
>
--
Neil n
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