Q: I measured 53degC in the airbox when idling in traffic, our bikes are designed to run lean, surely such a high AIT makes the bike run even leaner, just when a richer mixture would be safer.
A: Measuring the higher temperature won't make the mixture leaner, the idea is that if the actual air entering the combustion chamber is hotter. Let me digress for a moment.
The purpose of all sensors (TPS, RPM, Barometric & Air Temp) is to estimate how much oxygen will be in the combustion chamber at the moment of ignition. TPS & RPM are the biggest factors but higher barometric pressure or altitude result in more O2 getting packed in. Likewise, lower temperature air is denser and results in more O2 being packed into the combustion chamber. Therefore, Baro & Air are refinements to the TPS/RPM fuel table estimate. (The amount of fuel squirted is considered constant for a given time, except that the injectors turn on more slowly at lower battery voltage, so there is a correction for that.
So when the air in the airbox is 53C, it is less dense and needs less fuel for the same AFR.
Now if you have the sensor in fresh air, the ECU will overestimate the amount of fuel needed and over the next several seconds, the short term trims calculated using the O2 sensor will spot this "error" and reduce the fueling. Although the mixture gets "fixed", the short term trim is now biased to reduce fuel, possibly leading to a lean condition when you get rolling, until the short term trim fixes itself up.
Q: Most vehicles have the AIT arranged as close to the front of the vehicle as possible so as not be affected by engine heat.
A: This may be true when one sensor reports ambient air temperature to the display and air temperature to the ECU. However, the more accurately the IAT sensor estimates charge-air-temperature, the more accurately the short term trims are calculated.
Q: There is a pressure sensor built into the ecu, hot AIT combined with the atmospheric pressure would be sending conflicting signal to the ecu.
A: As I mentioned above, both pressure and temperature affect the amount of O2 entering the combustion chamber and both are helpful to accurately estimating the amount of fuel required for a given AFR target.
Q: Any AIT "spoofs" get adapted out because of the O2 sensor chasing that 14.7 AFR - now that we understand that the latest firmware goes to Closed Loop at 42degC, "spoofing" the O2 becomes even more important - until someone learns how to re-map the ecu.
A: An interesting point, even if you remap the ECU, the Closed Loop software will still bring the fueling to the reference point of the O2 (Lambda sensor).
