Effectiveness of RAM induction? (AFM replacement)

[Diehl, Jeffrey]

I was going to suggest much the same thing. I intend to run the two at the
same time on the car.  And build a tunable circuit to make the MAP look like
the AFM while I'm in the car.  That is, if the MAP outputs a frequency-based
signal, I'll convert it to voltage.  Then I'll adjust the scale with an
op-amp.  Then I'll have to plot volt v. rpm to see what kind of
(non)linearity I have.  I believe chips exist which will do log and exponent
functions on analog signals.  I'll bet they can be tuned to produce
different functions.  When the MAP looks like the AFM, the AFM is GONE!

Hey, talk is cheep, but this is what I'm thinking anyway.

Comments?

Mike Diehl.

-----Original Message-----
From: Phil Hunter
To: diy_efi at diy-efi.org
Sent: 10/12/2001 11:33 PM
Subject: Re: Effectiveness of RAM induction? (AFM replacement)

Mark Agnello wrote:
> 
> > Now here is what I'm planning to do...
> > From the TB, I'll go through a hot-wire MAP.  I'll
> > have to build a circuit
> > to make the MAP look like the AFM for the ECU.  
> 
> Jeffrey,
> 
> I am interested in doing something similar.  I have
> an All Trac Turbo. Same 3SGTE engine, similar
> restricted intake path.  Have you put any serious
> effort into figuring out how to emulate the AFM with
> a hot wire MAF? I have a spare AFM and I have been
> trying to figure out how to build a calibrated test
> bench that will allow measuring voltage vs airflow
> characteristics of the stock AFM.  Any ideas?

Here's what I'd do: forget the test bench, put a GM 3"
MAF in line w/ the AFM on the car so the same air has
to flow through both, the Grams/Second vs. frequency
out of the MAF has been posted recently so that's your
calibration, use something like a PIC micro to read
both the MAF frequency and the AFM voltage(s) for
datalogging, for the adapter have the PIC drive a D/A
convertor into the ECM, you can test your adapter by
measuring the voltage difference against the AFM while
it and the MAF are both are still in the car.

You might look back at what I proposed to adapt the
DIY-WB to a NB input, since this is essentially the
same circuit idea.

phil


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