Inlet Air Temprature Sensor Challenge

[WildMuskrat]

Hello,

Good day to everyone.

I am working on my porsche 911, 1983 SC efi conversion. Using the Microsquirt and all is well except that my Inlet Air Temprature Sensor is not being read at all by the ECU.
Using the GM-Open sensor from DIYAutoTune site. I have wired it directly to the harness and I am getting a proper resistance reading all the way through the cable up to the ECU itself. I have loaded the temp parameters and even went as far as to heat test the sensor myself. Still after loading the values, no joy. Every other sensor is working fine to include the cylinder head temp which operates the same way as the IAT. This is my last hurdle before I attempt the start.

Any ideas?

[msiddalingaiah]

What value does MT or TS show for IAT? Does it change if you disconnect your temp sensor? If it doesn't, there's a board problem.

[WildMuskrat]

There are no changes when I disconnect the IAT. The MAP sensor and the TPS sensors work perfectly. The coolant temp is stable and registering correctly. Not sure if there is a way to retrieve the temp table from the EUC to see if it even has the proper information. Have you seen this before?

[WildMuskrat]

Sorry, the value I am getting is always "0"

[Matt Cramer]

If you backprobe the sensor, what voltage do you get?

Also, exactly what sort of sensor are you using?

[msiddalingaiah]

It sounds like you might have a short on the board. You will have to trace it as Matt suggests.

[WildMuskrat]

I am not sure what you mean by voltage, I thought the sensor was resistance measured. The part I am using is the DYI autotune GM open IAT, the only number I can find is the 5040 number on the senor it self

Thanks

[trakkies]

I am not sure what you mean by voltage, I thought the sensor was resistance measured. The part I am using is the DYI autotune GM open IAT, the only number I can find is the 5040 number on the senor it self

Thanks

Voltage is applied to one side of the sensor and comes out the other at a different value due to its resistance. So if you measure one side to ground with a voltmeter, you''ll get 5 volts on the input terminal and somewhat less on the output (which varies with temperature). Doing this check shows if the entire circuit working - whereas measuring the resistance just the sensor.

[WildMuskrat]

Thank you for making this clear I was not sure how it read the resistance and now I have a good picture of it. I will check it tommorrow and let you know. Do you happen to know if the ECU is bad where I can get it fixed at? Since it is a microsquirt I am leary to break open the sealed case.

Thanks for all your help

[WildMuskrat]

Hello there, the voltage is 4.82 volts dc. Is this normal?

[trakkies]

Hello there, the voltage is 4.82 volts dc. Is this normal?

On both terminals of the sensor?

[WildMuskrat]

I believe so, I measured the voltage across the sensor. Went for one side to the other. Is there a particular voltage I should be looking for?

[Six_Shooter]

I am not sure what you mean by voltage, I thought the sensor was resistance measured. The part I am using is the DYI autotune GM open IAT, the only number I can find is the 5040 number on the senor it self

Thanks

Voltage is applied to one side of the sensor and comes out the other at a different value due to its resistance. So if you measure one side to ground with a voltmeter, you''ll get 5 volts on the input terminal and somewhat less on the output (which varies with temperature). Doing this check shows if the entire circuit working - whereas measuring the resistance just the sensor.

This isn't quite correct.

One side of the sensor is grounded. The other side connects to the ECU.

The ECU side (pin 20) has a pull up resistor internally that when using a DMM on this pin will show voltage. The ECU reads how little or how much voltage is on this wire, to calculate actual temp. As sensor warms up, resistance goes down, pulling the reference voltage down as well. So if you back probe the IAT/MAT sensor wire when the sensor is cold, you will see a higher voltage, than when the sensor is warm.

When using a DMM to check for volatge on this wire, it will show that the internal pull up resistor is installed and correct. If I'm reading the V2.2 board schematic correctly, the pull up resistor is attached to vref, which should be 5V, trhough a resistor, so you should see 5V or less on the MAT/IAT wire, without the IAT/MAT plugged in. With the IAT/MAT plugged in you should see less than 5V.

[trakkies]

Sorry, had a brain fart. You're absolutely correct.

[WildMuskrat]

OK, thank you for the very informative information, I am learning so much. I measured the voltage agian and with the IAT plugged in it was 2.72 volts. measured it without the IAT plugged in and it showed approx 4.87. So I believe the system is sending proper voltage and the resulting voltage is being affected by the resistance in the IAT. Leaving with the issue of the ECU not inerpting the correct thermo table that was loaded or something else in the unit is malfunctioning.