Pop-Quiz...

[Lou Faustini]

   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?   

    The -sensible- answer, at least for some sensors, is "Yes Lou, they are 
all alike..." If I was a design engineer for Ford I would insist on using 
all the same MAP sensors across the board for two reasons. 1- I could make 
20 million of the exact-same type, keeping tooling costs low. 2- It would 
make my dyno-testing much easier, by establishing company standard MAP data. 
Less confused engineers that way. 

   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. 

    The MAF sensors could be a different story though. Their Physical 
geometry is dictated by airflow.  A 5.7L Bronco motor will flow one hell of 
a lot more air than a 2.3L Mustang motor. You probably wouldn't want to use 
the same venturi casing on the MAF. Although, It wouldn't surprise me if 
there are only 2 or 3 different versions of the MAF sensor. I bet that they 
kept the electronic "guts" of the MAF the same across the board, again, to 
save money.

   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. 

    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?

    Any ideas?



     


                   --------> LF