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We get asked fairly often why we do not provide (or could we provide) IAT compensation for GM MAF sensors. The bottom line is that it's simply inappropriate to do so.

The GM MAF sensor does not require IAT compensation because it works in a way that takes air temperature and pressure into account automatically. This is the reason we provide an option to lock the IAT/Baro inputs when running with a GM MAS, thus freeing up both those inputs for other logging purposes.

This page is intended to provide some “proof” in the form of a couple datalogs illustrating how insensitive to varying air temperature the GM MAS really is. Both logs were captured on the same car on the same day using the exact same GM MAS.

One shows the engine running with air temperature in the 65-70F range while the other shows air temperature in the 160-170F range! The air temperature sensor on this car is located only inches away from the GM MAS.

Despite the large swing in air temperature, the GM MAS reading was nearly identical between the two logs. Fuel trim variation was less than 1% between them.

IAT near 65F
IAT near 165F

Hopefully this provides some reassurance to folks that the GM MAF sensors really do not require and would not benefit from additional IAT compensation. In fact, since the GM MAS signal is already accurate as air temperature changes (see datalogs), providing IAT compensation would actually mess the signal up.

So basically, we don't provide IAT compensation on a GM MAS because it simply doesn't need it.

gmiateffect.txt · Last modified: 2009/09/11 06:17 by twdorris