[Diy_efi] Re: Q regarding placement of a pressure sensor

[Kenny W]

The only problem with this is with the MAF, you get an 
absolute mass reading, and this doesn't correspond to 
the manifold pressure necessarily, since when using 
pressure you also have to compensate for temperature. 
By the time you've got all the code and algorithms 
rigged up to poll a MAP and IAT sensor and convert them 
to an equivalent MAF output, you might as well install 
a megasquirt or something. I'm kinda a newbie/idiot, 
but seems to me I asked about this once and this is 
more or less the response I got from Bruce and the 
likes. 
-Kenny

Quoting Bob Moon <yamahamoon at yahoo.com>:

> Thanks for the info.  
> 
> I understand that MAP and MAF are completely
> different, but I am not attempting to just
> replace the
> MAF with a MAP and call it a day.  I'm
> attempting to
> map the MAF signal to the voltage output of the
> MAP so
> I can use a uC to simulate the output of the
> MAF
> (square pulse wave, rather than a voltage). 
> That way,
> my ECU will still think it has a MAP.  
> 
> Since I am only interested in the amount of air
> flowing through the engine at that point in
> time, my
> question is this: for a given airflow count from
> a
> MAF, is there a given vac in the intake?  It
> seems to
> me that a given airflow will always have the
> same
> pressure signal, regardless of what's happening
> downstream of the turbo.
> 
> I know this is all possible thanks to the
> existence of
> various conversion kits (TRE's MASC and the VPC,
> for
> examples of two voltage-to-frequency
> converters).  I
> just don't know for sure where in the airstream
> I
> should place the MAP tap to get the most
> reliable and
> consistent readings.
> 
> Thanks again,
> 
> Bob Moon
> '92 Laser RS AWD
> 
> > Date: Mon, 15 Jul 2002 13:22:53 -0500
> > From: steve ravet <sravet at arm.com>
> > To: diy_efi at diy-efi.org
> > Subject: Re: [Diy_efi] Q regarding placement
> of a
> > pressure sensor
> > Reply-To: diy_efi at diy-efi.org
> > 
> > Bob Moon wrote:
> > >   I am thinking about converting from the
> MAF to a
> > MAP
> > > sensor arrangement.  Typically, the MAP is
> routed
> > to
> > 
> > You can't replace a MAF with just a MAP.  You
> need
> > some estimation of VE
> > in order to calculate MAF from MAP.  GM ECMs
> use a
> > table indexed with
> > both MAP and RPM.  You could also use
> throttle
> > position plus MAP (less
> > accurate).
> > 
> > --steve
> > 
> > 
> > -- 
> > Steve Ravet
> > steve.ravet at arm.com
> > ARM,Inc.
> > www.arm.com
> 
> 
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