Possible IAT Sensor scaling issues

[rocklizzard91]

I have a Link G4+ PNP ECU for my V9 EJ207 powered 2002 WRX, I am no longer running the factory MAF/IAT sensor in the intake and have fitted Bosch 0280130085 sensors (seemingly the same as Link IATB sensors). I have one in the turbo inlet pipe and one in the plenum (post throttle plate). I've been chasing a terrible heat soak issue for a long while that makes the car lean out at low speed/rpm until I get some airflow through the engine to cool it down. I was thinking maybe the issue is just that the sensor reads artificially high due to a lack of airflow through the plenum at idle (heatsoak) I decided to test my theory by putting a T1 Motorsport Air Temp Sensor (seemingly the same as Link's IAT1-8) in the top mount intercooler outlet, just before the throttle plate. However, now nothing matches and I feel more confused.

Running the T1 sensor on the Link NTC1-8 & IAT1-8 scaling and the Delphi AC IAT scaling resulted in the same temperature and read similar to ambient after the car sat for ~24h. The T1 sensor read 54* while the ambient was 65*, not perfect, but who knows how different the air is while in the intercooler I guess. It seems to be reliable and does support my theory that they are the same sensor. (T1 even advertises that they use the same scaling as GM IAT's).

However, running the Bosch 0280130085 sensor on the Link NTC12 & IATB reads noticeably higher than ambient (25* higher than the T1 sensor, reading 79* while air temp is 65*) Again, this was after letting the car sit for ~24h to stabilize temps with ambient. Running the Bosch sensor on the Std Bosch NTC scaling reads the same as the IATB scaling, and finally, the Bosch sensor on the Bosch 0280130017 scaling reads closer, but not identical (~7* off vs 25* off with the IATB scaling) the T1 sensor. The sensors are both mounted in aluminum parts (Intercooler and intake plenum) and are maybe a total of 6 inches apart, one on each side of the throttle plate.

My main concern is that the sensors on either side SHOULD be the same temperature, especially after sitting for 24h. This makes me think that the Bosch sensor is incorrectly scaled and it may be the main issue with my heatsoak problem. Maybe it's reading artificially high due to the scaling, not the sensor placement. That said, Here is the sensor data and checking those vs Links published sensor data in the manual and it matches the Bosch NTC scaling best, but even when I used a CAL table to manually input the sensor data, it still output values that match the IATB values and the Bosch NTC (side note, the Link sensor data isn't posted in the manual). Why does the Bosch 0280130017 scaling get me closer to the correct temp then?

So I guess the TLDR; is the IATB the same as the 028130085? If it is, why doesn't it match my IAT1-8 when the temps should be identical? Or at least more similar. FWIW, even while driving and going WOT, the sensors both should react fast enough to equalize with the amount of air flowing through them and they don't read the same then either.

I greatly appreciate any insight you all may have!

[Confused]

You're correct that in theory, they should read the same temperature when left overnight.

I assume both are pinned to An Temp inputs on the ECU, and both have the internal 1k pull-up resistor enabled (if it's one of the inputs where it's selectable)?

 

What I would do is eliminate the engine - unscrew all sensors from the engine, and place them next to each other, and then also apply heat, such as from a hairdryer, and you should then see them both increase in temperature readings pretty much the same once they stabilise.

You can also look at the raw voltage readings coming from the two sensors.

Finally, switch the two sensors between the two inputs, and see whether the "issue" follows the sensor or the input.

[Adamw]

7 hours ago, rocklizzard91 said:

is the IATB the same as the 028130085?

Yes our IATB is the same part number, a common VAG sensor.  The manufacturer quoted calibration curve for the 028130085 is ever so slightly different to the common "Std Bosch NTC" but only really significant below 0°C and they have a large tolerance at low temps also, so most manufacturers including us just consider it the same curve.  2.4-2.5Kohm at 20°C.

The Bosch 0280130017 calibration is very rare, as far as I know it was only used for a cyl head temp sensor on an air-cooled Porsche for a short time period.  ~1.65Kohm at 20°C.  This should not give correct results with your sensor.  

The Link NTC1/8 is very similar to the common Delphi/GM calibration. ~3.5Kohm at 20°C.

The first thing I would do is measure the resistance of your 028130085 at 20°C (normal room temp), it should be close to 2400ohm.  The official range is 2290-2551ohm.  There are some pretty low quality clones around.