01-24-2009, 12:41 AM
Join Date: Sep 2007
Location: Detroit, MI
Total Cats: 0
Inaccurate IAT Calibration for MSPNP9093 Running No AFM Flash
I recently got my turbo on my car, and switched over to the GM open element IAT sensor. I flashed the MS with the "without AFM" setup, which, I believe, is set to read the GM open element IAT sensor. The default flash is not properly calibrated for the GM IAT for temps below ~43F. I noticed my water temps at key on was 32F, which was also verified as ambient on my garage heater thermometer. However, the IAT registered 42-43F, and would not read any lower.
I had to reflash the MS with new EasyTherm values (finding the boot jumper was a bit of hunt). Now, the IAT sensor reads within 2F of the CLT at ambient (34 vs 32, respectively).
The chart below shows overlays of the GM IAT Default EasyTherm values vs. the MSPNP9093 w/o AFM IAT *inc calibration. The two curves are reasonably close for everthing between 50F to 200F, which would work well for most people. However, for those like me, running in sub-freezing temps, you can see that the calibration tables deviate significantly below 50F.
For my new cal, I used GM IAT default EasyTherm values. For the Miata CLT, I used the following EasyTherm values:
; Generated using EasyTherm 5
; Coolant -Miata CLT
; File generated for use with stock 2490 ohm resistor at R7
; Steinhart-Hart coefficients: A= 1.131957E-03 B=2.943506E-04 C= -3.725285E-08
; Input Data: Temp, degF Resistance
; -4 16150
; 104 1150
; 176 330