IAT Scaling - 2.49 koHm pull up resistor vs 1 kOhm

[m3gusta]

I have a G4X Fury wired to a BMW S52 motor with a plug and play adapter harness.

I am using the original IAT sensor and am trying to calibrate it for accurate measurements. The Bosch calibrations are not accurate for the IAT although ECT is accurate.

I have found the sensor scaling table for the S52 OEM ECU and inputted that data, however the reading is still inaccurate.

I'm of the understanding that this table is only accurate for a pull up resistor value of 2.49k oHm. With only a choice of 1k or 10k oHm, how can I convert this table to be accurate for a 1k oHm pull up resistor?

Thanks for any and all help. Total newbie here but trying to learn as much as I can. 

[Vaughan]

The combination of pullup resistor and the temperature sensor make a resistor divider with a fixed resistance value from 5v to the ECU Analog channel and the varying value of the temperature sensor from the ECU Analog Channel to ground. This means that if you know the pullup resistor value, the voltage it is attached to and the voltage at the ECU Analog Channel then you can calculate the resistance of the sensor.

Voltage at ECU channel = pullup voltage * sensor resistance / (sensor resistance + pullup resistance)

With some trickery this becomes:

sensor resistance = (Voltage at ECU channel * pullup resistance) / (pullup voltage - Voltage at ECU channel)

You can use this to convert your voltage calibration values to resistance calibration values and then setup the calibration in the ECU in resistance or convert it back to voltage calibration values but to suit a different pullup resistor value.

Quick bit of maths says:

141 -> 109ohm

110.2 -> 258ohm

95.2 -> 392ohm

80.2 -> 615ohm

70.5 -> 866ohm

60.8 -> 1238ohm

and so on

[m3gusta]

Thank you so much, this is really helpful.