SPREADSHEET: GM IAT

bcheck555 · **Joined:** Thu Jan 29, 2009 11:16 am **Posts:** 523

Since there seems to be a lack of any kind of scaling for the GM IAT sensor, I put together this sheet. To find the value of the internal resistor of the ECU, I threw a resistor of known value in place of the IAT sensor, measured the voltage and back calculated. I believe the circuit is a simple resistive divider http://en.wikipedia.org/wiki/Voltage_divider#Resistive_divider

Trying to find usable values for the sensor is the challenge now. The values from the GM datasheet are unloaded values. I found slightly different values at http://www.diy-efi.org/gmecm/component_info/sensors.html. Not sure how much difference there is between loaded and unloaded values there is, maybe an EE can chime in?

If anyone has better values for the GM please post. Thanks.

The excel add-in from http://www.trimill.com/TriLookup/TriLookup.htm is required...

See post 11 for values I am currently running.

mrf582 · **Posted:** Thu Nov 10, 2011 3:35 pm

http://forums.nasioc.com/forums/showthr ... ?t=2211639

Reuna wrote:

I'm using:

Code:

[Table2D]
0.21    0.36    0.52    0.67    0.83    0.99    1.14    1.30    1.46    1.61    1.77    1.92    2.08    2.24    2.39    2.55    2.71    2.86    3.02    3.17    3.33    3.49    3.64    3.80    3.96    4.11    4.27    4.42    4.58    4.74
248,0    248,0    237,4    219,2    203,8    191,2    181,1    171,5    162,8    155,2    147,7    141,1    134,4    127,9    121,9    115,8    109,6    103,9    97,6    91,7    85,1    78,3    71,4    63,6    54,9    45,5    33,7    19,1    -4,9    -40,0

Don't know if it is exactly right at all operating temps but seems to match ambient temp when engine is not running. The sensor is mounted to intake manifold.

I had to adjust "Speed density load compensation (IAT)" a bit in order to get consistent AFRs throughout different temperatures:

Code:

[Table2D]
-40    -22    -4    14    32    50    68    86    104    122    140    158    176    194    212    230
34,34    28,89    23,82    19,10    14,70    10,62    6,81    3,27    2,97    -0,12    -3,01    -5,73    -8,31    -10,75    -13,09    -15,36

It seems Mitsu EVO ECUs use an internal resistor divider of 2.2-2.3kOhms for the MAT sensor. A couple people have mentioned Subaru uses a 1kOhm internal resistor divider. What value did you come upon?

bcheck555 · **Joined:** Thu Jan 29, 2009 11:16 am **Posts:** 523

Thanks, added to sheet, graph follows the diy-efi for the most part. Upper and lower then follow the WRX/GPN sensor.

bcheck555 · **Joined:** Thu Jan 29, 2009 11:16 am **Posts:** 523

mrf582 wrote:

It seems Mitsu EVO ECUs use an internal resistor divider of 2.2-2.3kOhms for the MAT sensor. A couple people have mentioned Subaru uses a 1kOhm internal resistor divider. What value did you come upon?

1229 Ohm

gaby · **Posted:** Fri Nov 11, 2011 12:11 pm

I paste the values and logged it last night. 60-70 degrees driving, 90-100 idling with a FMIC. AFR's look stable, I will drive today when is warmer outside to log again.

bcheck555 · **Joined:** Thu Jan 29, 2009 11:16 am **Posts:** 523

gaby wrote:

I paste the values and logged it last night. 60-70 degrees driving, 90-100 idling with a FMIC. AFR's look stable, I will drive today when is warmer outside to log again.

The lower values are probably where you will run into problems. It was 33 ambient and logger was showing 41.

gaby · **Posted:** Sat Nov 12, 2011 11:45 am

mrf582 wrote:

http://forums.nasioc.com/forums/showthread.php?t=2211639

Reuna wrote:

I'm using:

Code:

[Table2D]
0.21    0.36    0.52    0.67    0.83    0.99    1.14    1.30    1.46    1.61    1.77    1.92    2.08    2.24    2.39    2.55    2.71    2.86    3.02    3.17    3.33    3.49    3.64    3.80    3.96    4.11    4.27    4.42    4.58    4.74
248,0    248,0    237,4    219,2    203,8    191,2    181,1    171,5    162,8    155,2    147,7    141,1    134,4    127,9    121,9    115,8    109,6    103,9    97,6    91,7    85,1    78,3    71,4    63,6    54,9    45,5    33,7    19,1    -4,9    -40,0

Don't know if it is exactly right at all operating temps but seems to match ambient temp when engine is not running. The sensor is mounted to intake manifold.

I had to adjust "Speed density load compensation (IAT)" a bit in order to get consistent AFRs throughout different temperatures:

Code:

[Table2D]
-40    -22    -4    14    32    50    68    86    104    122    140    158    176    194    212    230
34,34    28,89    23,82    19,10    14,70    10,62    6,81    3,27    2,97    -0,12    -3,01    -5,73    -8,31    -10,75    -13,09    -15,36

It seems Mitsu EVO ECUs use an internal resistor divider of 2.2-2.3kOhms for the MAT sensor. A couple people have mentioned Subaru uses a 1kOhm internal resistor divider. What value did you come upon?

Did you try this values. It hasn't got colder that 48 yet here in Tucson.

bcheck555 · **Joined:** Thu Jan 29, 2009 11:16 am **Posts:** 523

I am running a modified version of the diy-efi values. The low end really needed work. I am ordering a power supply, thermocouple logger and voltage logger. Plan on building a circuit and measuring the temp/voltage directly...

gaby · **Posted:** Tue Nov 15, 2011 8:42 pm

bcheck555 wrote:

I am running a modified version of the diy-efi values. The low end really needed work. I am ordering a power supply, thermocouple logger and voltage logger. Plan on building a circuit and measuring the temp/voltage directly...

Let me know the results. I not going to be able to test it prior to January. I'm might go do a mountain run to test the cold side of this table.

mrf582 · **Posted:** Sat Nov 19, 2011 12:10 am

Can anyone post the values in this thread for those of us that don't have or necessarily want to get the trilookup function thing for Excel? This will also help posterity.

bcheck555 · **Joined:** Thu Jan 29, 2009 11:16 am **Posts:** 523

PVC tube, shop vac, dry ice, heat gun, spare gm iat, thermocouple and volt meter. I let the temp and voltage stabilize as much as I could. Hope this helps someone...

Carbibbles · **Joined:** Tue Aug 30, 2011 3:17 pm **Posts:** 900

^^ Was the GM IAT connected to the ECU when you did that testing? Wondering if that would make a difference. I could send you a logger def that logs IAT volts directly as the ECU views it, if you feel like verifying a couple temp points through the ECU?

bcheck555 · **Joined:** Thu Jan 29, 2009 11:16 am **Posts:** 523

Carbibbles wrote:

^^ Was the GM IAT connected to the ECU when you did that testing? Wondering if that would make a difference. I could send you a logger def that logs IAT volts directly as the ECU views it, if you feel like verifying a couple temp points through the ECU?

It was and it does. You can send them, but not sure when I will set everything up again. I need to work on IAT comps again...or at least decide if I should use these vice what I have for comps and scaling, which is not working too badly...

ride5000 · **Joined:** Thu Aug 03, 2006 10:40 am **Posts:** 1934

bcheck555 wrote:

PVC tube, shop vac, dry ice, heat gun, spare gm iat, thermocouple and volt meter. I let the temp and voltage stabilize as much as I could. Hope this helps someone...

thanks for your work!

ken

crazymoet · **Posted:** Mon Feb 20, 2012 11:11 pm

thank, nice work.

RomRaider

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