Custom MAF system: help w/ calculations

[Carl Summers]

If you have a particular MAF device, and I have the transfer function
already logged, let me know.  I may be of some help.
-Carl

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Scot Sealander
Sent: Wednesday, January 24, 2001 2:59 AM
To: diy_efi at diy-efi.org
Subject: Re: Custom MAF system: help w/ calculations


james.drysdale at utoronto.ca wrote:

> I'm implementing a MAF system on the vehicle, and would like to know
> if I can tap into your expertise (or if you can point me in the right
> direction) regarding the calculation of the pulse width of the fuel
> injector for a MAF system. There's a lot of good info on the efi332
> website, but it's a speed/density system.

It is just too simple.  The MAF will output a frequency or voltage that
corresponds to airflow.  The ECM will convert that value to gps.  If you
sample the MAF once per engine cycle, and then divide gps by rps, you
will
get:

 (grams/sec) / (Revs/sec) = grams/rev

You do 2 revs in an engine cycle.

Convert the mass of air to mass of fuel needed by dividing by AFR.

grams of air/AFR = grams of fuel


To get injector PW, use the injector constant.

grams of fuel * (n sec / gram) to get PW in sec


Then compensate for injector on/off, and inject it.

The real problem is getting a MAF to read the airflow you are going
to have.  All these values will not be in grams.  Much lower than
that....

Scot Sealander
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