Mass airflow sensors.

[nacelp]

Don't run a GM MAF dowstream of the turbo.   Matter of fact I wouldn't run
anything downstream of except possibly a throttle body.  Lose a seal and
loose a MAF, no thanks.  The hot wires and films don't clean as cherry as
you might think.  While now terribly illegal the GM early method was blowing
the MAFs out with Freon.  The is I was told, that ther is a chemical
reaction to oil and the films.  They used a burn off system in the early GMs
when they were exposed just to atmoshpere..
(I used films to mean both types).
Just my 2 cents worth.  Also, MAPs are about $100 cheaper then a MAF  ($40
vs 140, typ min)
Thinking that your (or anyone) is so much better then the .01 is a mind trap
(notta flame, but I did play this game, and typically what feels faster is
slower too, the major co. capitalize to the max on fooling ones senses,
doubt me?, drive a late S/C Gran Prix, or STS).
Grumpy

----- Original Message -----
From: Andrew Brownsword <asword at telus.net>
To: <diy_efi at diy-efi.org>
Sent: Saturday, February 19, 2000 9:21 PM
Subject: Re: Mass airflow sensors.


> Thanks for the additional input... I want to get as much information on
the
> tradeoffs as possible before making the leap.  I can always switch if
there
> are problems, but that is going to be costly!
>
> The response time isn't an issue for driver sensitivity (although I know
> from experience that I'm sensitive to a much shorter interval than 0.1
> sec!), it is more important to avoid leaning out.  The existing ECU,
> however, has acceleration enrichment that is triggered by an increase in
> RPM.  I'd have to double-check but I think it also has a TPS enchriment
> table.  It couldn't cover a 200 ms response time, but it could cover a
> couple of milliseconds with no problem.
>
> Another VAF->MAF converter doesn't seem to think that running the MAF
under
> pressure (only 6-7 psi of boost) will be an issue... and his empircal
> experience suggests that the MAF is, if anything, more responsive than the
> original VAF.  There is also the issue of crud & oil deposits from the
turbo
> accumulating on the MAF sensor, but he doesn't think cleaning it
> periodically is a major issue.  I'm really interested in hearing other
> opinions on these issues.
>
> Advantages of the MAF approach are:
>
> - Considerable amount of output data is available
> - Cheaper & wider part selection; easier to replace if it fails
> - Generates output across the full 0 - 5 volt range, taking maximum
> advantage of the input 10-bit DAC
>
> Advantages of the Link AFM:
>
> - Programmable
> - Not vulnerable to vacuum leaks
> - Certain to work in a boosted application (without cleaning)
>
>
> Now I'm off to search the archives for info on this topic.
>
> Thanks,
>   Andrew
>
>
> > Just some numbers to mull over while your thinking this thru.
> > Joe Average driver thinks .1sec is an instanteous response.  The best of
F1,
> > can detect .01 (I think it was Senna, that set this "record").   This is
> > just in reference to engine response.
> > The 200 msec., might be to fully stabilize, on the hot style sensors but
a
> > good part of that is smoothing to a level you'll never notice/see.  The
> > transistional delay to airflow is several msec., as I've heard reported.
> >   There is no AE (or little, to none), on the gm MAFs, yet on the MAPs
there
> > is MAP AE, Coolant temp AE and TPS AE.  (AE=Accleration Enrichment).
> >   If your system is looking for a V difference, how does the Ford MAFs
line
> > up?.
> > Can you get a Ford sensor and put it in parrarell with your door sytle
> > sensor and compare them, and then use your existing code (with changes)
to
> > "read" the other sensor?
> >
> >> Hmmm... this is a strong argument for converting to speed/density.  The
> >> pressure change should be instantaneous -- or at least as fast as the
VAF
> >> signal change.
> >>
> >> > How about adding a MAP sensor, and looking for a sudden change in
that?.
> >> >
> >> >> I'm also working on converting my AFM to MAF but I've ran into a
> >> >> couple problems that I don't see mentioned here.  The response
> >> >> time of the AFM to changes in air flow is almost instantaneous.
> >> >>
> >> >> Any thoughts?  BTW the car is an 88 BMW 535i if that helps.
> --------------------------------------------------------------------------
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