[Gmecm] GMECM MAT calibration

[Rob Handley]

Call me sad but, returning to my analysis of MAT calibrations from a year 
ago in preparation for my long overdue move to EFi, I think I have moved 
forward. I'd be grateful if somebody could sanity check where I've got to:

If I'm right:

- $8D code has a lookup array that converts the 8 bit complement of raw MAT 
AtoD value to a scaled MAT temperature value (which can be converted to 
degrees C using the same formula as CTS ie. (lookup value * 0.75) - 40
- $58 code has no such lookup array - so the AYBN_hac.src and 
58_disassembly.src hacks have some other lookup array wrongly identified as 
a MAT lookup array. Interestingly, AYBN_hac.src has a MAT AtoD to degrees C 
conversion array inserted purely as a comment. When plotted, this matches 
very well with the $8D lookup array. The version at 
http://www.diy-efi.org/gmecm/component_info/sensors.html matches less well - 
below 50C.
- $8D code mostly uses the scaled MAT temperature value for indexing into 
other arrays.
- $58 code uses the raw MAT AtoD value for indexing into other arrays.
- $8D code puts the 8 bit complement of raw MAT AtoD value in the Mode 1 
ALDL message.
- $58 code puts the raw MAT AtoD value in the Mode 1 ALDL message.

I find it strange that one version of GM code calculates a MAT temperature 
and another doesn't. I know it doesn't matter, as long as the comparison 
values are right but... I also find it strange that a version of GM code 
that does calculate MAT temperature ($8D) doesn't output that temperature 
value in the ALDL message - so, to compute it, you have to do a calibrated 
lookup in your monitor code! :-( Why should MAT be any different from CTS?

Am I right in thinking that the Corvette ($8D) and Sunbird ($58) 
installations used the same/equivalent MAT sensor? Is the same MAT sensor or 
MAT sensor calibration used in most of the GM ECM installations?

How much can these MAT sensors be bought for new/scrap? Does anybody know if 
there is a handy source of equivalents that I could cheaply buy in the UK?

Rob