Bosch to Hitachi MAF

[RABBITT_Andrew at mv8.orbeng.com.au]

>the existing bosch MAF is setup to be wide open (0 volts) at engine 
>peak torque (3200).  It may flow about 220 CFM at this point.  On the 
>other hand, the Hitachi MAF may be able to flow 500 CFM, so a way 
>needs to be found to adjust the voltage signal (besides inverting 
>it), that the ECU would see. 

If 220CFM is 0V, then how is the ECU going to determine anything more 
than that (ie: negative volts).  The way it looks to me is your ECU is 
limiting your airflow as much as your AFM.


>Assume that we have measured the voltage output of both units at 10 
>and 220 CFM (assume air temperature is equal).  The Bosch puts out 
>4.7v at 10, and .3 volts at 220 CFM.  On the other hand, the Hitachi 
>puts out .5v at 10 CFM and 3.6v at 220.

Like all other MAFs, the Hitachi unit (I presume it's a bypass unit 
similar to that fitted to the previous model Taurus, and many other 
Fords), is non-linear and therefore a 2-point calibration will not be 
adequate.

Also, at large throttle openings, the signal jumps around a bit, and 
the only way I know of getting around this is to purposely alias the 
signal by sampling synchronously at a pre-determined crank position. 
(I'm assuming a digital controller)

Setting this up is no easy task (speaking from experience here) and if 
you get it wrong, you'll likely be out by more than 100% in some areas 
of the speed-load map.

Andrew Rabbitt
Orbital Engine Company
PERTH Australia