Air Flow Meter Modification

[Jeffrey Engel]

There was an earlier discussion along the lines of  AFM vs MAF.
At the time I was interested in replacing my AFM with a MAF 
unit.

To replace the AFM with a MAF would involve absolute air pressure, 
temperature and velocity.  Since the BAP and air temp sensor are 
there anyway, you should be able to use them as inputs along with the 
MAF to output an AFM signal to the computer.  Somewhere along the way 
I decided to put up with the AFM restriction, but if there is 
interest in making a convertor include me in.

An alternative would be to reprogram the ECU to accept MAF values 
directly.  However, I can't get the 8061/5 op-code description. . .

> From:          "Terry McLane 312.630.0533" <MCLANE.TERRY at ntrs.com>

>     The L-Jetronic transmits a "wave" pattern, as the air opens.  
>     Interestingly enough, if you look at the specs for a particular car, 
>     (All-Trac Turbo for example), it says when the air meter is closed, 
>     resistance should be 400-600 ohms.  When wide open it should be 20-2000 
>     ohms!  There are (as I remember) about 8 different gradations in the 
>     meter, with a linear resistance in between.  Supposedly, each gradation 
>     is a fixed multiplier of air (logarithmic) like step 2 is 3 times more 
>     air than step 1, and step 3 is 3 times more than step 2, etc.
>
   <plunder / pillage>
>     
>     If you're more ambitious, you could always build a circuit using one of 
>     the non-restrictive Hitachi MAF sensors, use a Pic16 or 68HC11 and a 
>     D/A converter to map the MAF output to the meter output, build a table 
>     and then send it to the computer.  Since the MAF already adjusts for 
>     temp, you could then use a potentiometer on the thermistor leads, 
>     giving the ability to tune the entire fuel curve by making the ECU 
>     think the air is colder (richer) or warmer (leaner).
>     
>     If anyone has any other solutions, I'd like to hear them as well.
>     Terry