Intake air temperature sensor replacement

[rng3]

The stock Intake Air Temperature sensor (IAT) is mounted in a location to monitor the Air temperature entering the engine. It is one of the several sensors the ECU uses to to determine how much fuel to inject at any given time. When you switch to 3 separate air cleaners such as K&Ns you need to find a suitable location for the sender. Just hanging it from the fuel rail may not give accurate readings. Somewhere on this forum there was a picture of the stock sender mounted to the top of a K&N.

The IAT is simply a NTC thermistor (negative temperature coefficient) resistor Thermistor - Wikipedia
a resistor that the resistance changes with temperature.

Most NTC seem to be rated by their resistance at 25 deg C. There is also the temperature range, curve, resistance tolerance, etc.
NTC can be quite small and inexpensive. Maybe a 1/8” diameter. I have purchase several 2K, 2.1K 2.2K to compare to the stock.
I put them and the stock unit in a plastic bag submersed in a container of heated water and compared the resistance reading at various temperatures. I got pretty close. I then mounted the closest NTC bead on a small tube and drilled a small hole in the bottom of the center air cleaner to put it right in the air flow.

What I was wondering is if anyone knows the correct NTC to use to mimic the stock one. So far one of the 2K seems to be the closest. With some after market fuel injection kit you set the value at freezing and then boiling water and the computer determines the curve. We do not have that luxury here.

Thanks,
Rick

 

[Claviger]

Good work and good post! How far off was the 2K?

 

[rng3]

Good work and good post! How far off was the 2K?

I can post some results tomorrow when back in office.

Rick

 

[rng3]

Temperature in deg F from infrared thermometer
Temp, stock, 2k NTC
133 .612K .600k
116 .845K .878k
100 1.181k 1.224k
98 1.192k 1.229k
97 1.257k 1.294k
94 1.385k 1.413k
91 1.463k 1.503k
78 1.870k 1.911k

 

[leatal]

Temperature in deg F from infrared thermometer
Temp, stock, 2k NTC
133 .612K .600k
116 .845K .878k
100 1.181k 1.224k
98 1.192k 1.229k
97 1.257k 1.294k
94 1.385k 1.413k
91 1.463k 1.503k
78 1.870k 1.911k

I simply bought a Bosch unit for BMW cars on Ebay for $23. From sitting in the hot sun to chilled in the refrigerator, it seems to stay about 1/2 to one degree cooler than the stock unit (ECU reading). It is more durable than stock (bulb covered in plastic), has a smaller mounting hole (approx. 1/4 inch) with a longer probe, and has the same plug as the OEM. I use it in the front of my Carpenter intake exposed directly to the incoming air flow and seems to work well.

 

[rng3]

That is interesting, can you post the part number?

Rick

 

[BigNorm]

I just re used the stock one. I drilled a hole in the right side cover, stuck the sensor through and held it in place with a K&N filter and a hose clamp.

I'm pretty simple. What is the advantage to using another air temp sensor?

 

[leatal]

That is interesting, can you post the part number?

Rick

The part number is: Bosch 0280130039. Actual price was about $18.00. Advantage is smaller size, more robust, and cheaper than OEM. Cheap enough for some with knowledge about this kind of stuff to purchase and test properly.

 

[Claviger]

From looking at your numbers, you coincidentally caught the point where the two curves cross, at 133 the delta inverts, so it probably crosses right at 125 or so.

The deltas are minor, and, I wouldn't hesitate to use the 2K for a second with one caveat. Check the resistance of both AT 100c/212f.


A few degrees here and there will make ZERO difference in how the bike runs while warming up, or while on the move on the freeway.

 

[rng3]

I just re used the stock one. I drilled a hole in the right side cover, stuck the sensor through and held it in place with a K&N filter and a hose clamp.

I'm pretty simple. What is the advantage to using another air temp sensor?

I was hoping to supply the ECU with accurate temperature information of the air actually entering the engine. The stock sensor is kinda bulky, the lead is short so locating the sensor in the incoming air stream is tricky.
It is pretty hot under the bearclaw. So if you run without the bearclaw with tall air filters exposed to cooler air the ECU may not be getting the proper temperature information that it uses to calculate how much fuel to inject.
The NTC itself is tiny perhaps an 1/8" in diameter so it can be located almost anywhere and just solder leads any length you want and rout to the plug. The cost around $1.00 or less.

Rick