Pop-Quiz...

[Bohdan L Bodnar]

>   Ok, here are some nagging question I want to share..
>
>    Are the MAP and MAF sensors that are mass-produced by auto makers all 
>calibrated the same? (among the same manufacturer) More specifically, can I 
>take my MAP sensor calibration data from a Mustang and expect to see the 
>same " cal curve" on an Escort's MAP sensor?   

Yes (for the latter question).  Send me e-mail if you want the
frequency-to-pressure relationship for Ford's MAP sensors.  Atmospheric
pressure will correspond to something between 150 Hz and 155 Hz (pressure
dependent).

>   I have a Chiltons manual that implies that all Ford MAP's are the same. 
>It also implies that the MAT and ACT, and ECS (coolant) sensors are 
>equivalent to each other, as well as across the board. That makes sense too, 
>because you could use one look-up table, and one subroutine in your 
>software, to take all three readings. You would also buy 30,00,000 of the 
>same thermistor, and save a bundle of cash. The only difference would be the 
>packaging. 

This is correct.  The same thermistor is used, but the packaging is
different.


>   I also know, (on the cars I have seen) that GM uses a MAP sensor that 
>provides a voltage output. Same for Toyota, and Mazda. Ford likes to send a 
>frequency that is proportional to the pressure. I guess that offers better 
>noise immunity. (Although it -may- cause some EMI) The frequency approach 
>also requires one less ADC channel. 

GM also uses a variable-frequency MAF sensor (max frequency is around 3 kHz).
The original variable-frequency MAF sensors were made by Hitachi.  Delco now
has one out which is also a variable frequency sensor.  Externally, the
variable frequency MAF sensors are smaller than the older Bosch heated wire
ones which GM used.

>    Last question: 
> 
>    I was buying an EGO sensor for my Mustang. When I went to the friendly 
>Ford dealer (NOT) I was asked for a "Calibration code" that is part of the 
>VIN on the car. Why was this necessary? Aren't all EGO's the same? I thought 
>they sort-of had to be, because of the gas detection method. Why not (see 
>above arguments) make -all- EGO's calibrated the same, and then use your 
>software (which has to be unique anyway) to interface the EGO to the engine 
>setup?

Physically, there isn't much difference among O2 sensors.  Solid state
electrolyte theory (on which the modern O2 sensor is based) was very well
developed by the mid 1950s and the mechanism of oxygen ion transport was well
understood (*lots* of theory and empirical data available then).  My Mustang
has a Tomco aftermarket sensor (which is nothing more than a GM O2 sensor).
Ford requires "calibration codes" for EVERYTHING, no matter how trivial.

Cordially,

Bohdan Bodnar
bohdan.l.bodnar at att.com