[risen]

I was actually looking into this for a piece of datalog software I'm working on. Below is a thread with some info about the resistor in the charge temp circut, and it says that it's bias resistor is 5k ohms, not 10k. So perhaps that's the problem with your final table?

http://www.turbododge.com/forums/f4/f60/79453-charge-temp-coolant-temp.html

Anyways, I just used easytherm to generate a table with an adc -> temp map based upon the 3 ohm ranges in another post here on td.com. I've pasted the header with the calculated coefficents. I can paste the whole map, but you can easily reproduce it with easytherm, and it's pretty big. The adc table does look to be accurate compared to all the other info I've seen.

; Generated using EasyTherm4.exe
;
; Coolant Thermistor Comment Field
;
; ***** CAUTION - NON STD BIAS RESISTOR REQUIRED *****
; File generated for use with 5620 ohm resistor at R7
;
; Steinhart-Hart coefficients: A= 1.134887E-03 B=2.32812E-04 C= 9.580155E-08
;
; Input Data: Temp, degF Resistance
; 32 32500
; 77 10000
; 212 680
;

 

[risen]

a different value bias resistor is applied over a certain temperature range too, in an attempt to make the scale a bit more linear. i dont remember exactly what the value and switch point are, but its documented in the code for at least one of the computer families.

I have been looking @ the 87 T2 code over the past few days and in the MM_DetermineCoolantTemp_v subroutine it handles the switchover and calc of temp from sensor. From the post I linked to above it looks like it's 10k ohms for cold (< 125F) and 1k ohms for hot. The constant in the function for the switchover is #$dc, in case anyone's interested.

That is for the coolant temp sensor though. I've looked at most of the code where the RawAirTemp value is referenced and I don't see any of the ioPortxxx values being written to. I don't think that the charge sensor gets switched. Am I missing something?

I did calculate the curve for the sensor from the easythrem output and it best matches a cubic with negative coefficents. It has a rather sharp range in the middle and flatness twards the ends. It looks like a reverse narrowband graph, sorta. Since the data seems to make sense, I'm going to take the table easytherm generated and use that as a lookup for the RawAirTemp. I'm planning on doing some confirmation by checking the value of the coolant and the air temp on various temperature days before the car has been started so everything is the same temp.

Now, does anyone know how to convert the battery temp sensor's value in the '87 cars to a real value? If not, no biggie, I'm going to try and curve fit that one too.