RomRaider

I thought I would contribute my data and scalings and spreadsheet. Take it as you wish.

Going from my swapped RS to a friends WRX we found the internal resistances to be different. Mine was 1291 Ohms and his was 1244 Ohms, which skewed the temp scaling a little. My spreadsheet shows a lot of GM data, calculations, comparisons, and graphs addressing this as well. Enjoy.

Edit: Added 0-4.7v data after measuring the voltage at the plug for the IAT sensor. I found an article for earlier this year from Cobb about this as well as Airboy.

So is post 11 our best bet? ie Is this working for most generally speaking or are there no definite values? I have a GM sensor finally and am putting it on my 05 STi.

Looks like it.

I have perfect results with the values ryanr posted...

Awsome, thanks.

I just installed my GM IAT, and at my temps (10C / 50F), and just wanted to share my results. Ryanrs values were quite far off for me (about 20C off), while Bcheck555s values was spot on at my temps. This was a 02WRX ECU.

This info should be in a sticky or something.

I didn't find this Thread until yesterday. I wasn't happy with the funny IAT readings I was getting w/the standard scaling. I performed a similar test as Bcheck555 did, Except I used a cardboard box, a multimeter, a thermocouple, heatgun, and a dc fan. I didn't think of getting dry ice to get the cold temps. So I don't really have any cold temps. I measured voltage @ the IAT connector which is about 1' down line the sensor it's self. BCheck555 never reported back with his findings using carbibbles IAT Voltage logger defs. So I'm not sure how different the readings are from the ECU. On my rig, temps fluctuated by a good 5 *F, but I feel like my readings @ the higher temps are very close.... not that there are many people driving around in 150 - 200*F heat.



I measured a internal resistance of 1005 ohms, so I don't think I can use Bcheck555's since he has an internal resistance of 1229.

I put my data into a modified version of RyanR's spreadsheet.

This is my first time using the IAT in the intercooler so I'm redoing my VE Table. I haven't had much luck yet. I didn't change my IAT load comps, so maybe that could be the issue. I need to figure out how to modify that.

Edit: went outside and measured temp and monitored IAT... engine dead cold. IAT read 16-18*F and actual temp is 3*F. I wish I had thought of the Dry Ice!

Running my IAT Scale and not changing the IAT Load comp made the fueling too lean. I went back to a suggested IAT scale & Load comp because it's proven to work year round. I would love to get a IAT scale that is both accurate and effective, but that requires extra tuning and I just don't have the time. Anyone out there w/a V7/V8 ECU w/a calibrated IAT scale & Load Comps to match, please post up!

I'm using the 'calculated' GM IAT resistances (spreadsheet by ryanr) and after letting the car sit for more than 12 hours in a cold ass garage, my ECT, IAT, and EGT (measured via digital IC MAX6675) all measured 55F.

I'll be leaving the car outside tonight and if I can get myself to go in the expected 22F ambient weather tomorrow morning, I'll recheck and report back.

WRX ECU or JDM STi ECU?

Has anyone tried this scaling with the IAT sensor from T1racing, The folk are Injector Dynamics? It supposed to be calibratred the same as a GM IAT sensor. I have this sensor but havent tried it yet.

Did some measurements on my 2006 USDM WRX and found that the internal resistance is closer to 940 Ohm. I made three measurements with different resistor values (3.3k, 1k, 470) and each one would give a different internal resistance if I assume a supply voltage of 5V. Then I measured the open circuit voltage at the harness and it was 4.78V instead of 5V. Using 4.78V in the calculations gave internal resistance value of ~940 for all three measurements.

Made a couple of measurements of the resistance of the MAF IAT sensor element as well. One at ~60F and the other ~35F (in the fridge for 20 minutes, with wires extended). Temperature was checked with an infra red thermometer). The results lines up with the stock calibration table really good, using 4.78V and 940 Ohm series resistance.

makes sense. do not assume the supply rail voltage for the sensors is 5.0000v. measure it!

Did a similar measurement on a R35 GTR and the open circuit voltage was also 4.78V. Using a 1k resistor and the voltage drop across it gave an internal resistance of ~940 Ohm as well.

Have you tested the GM IAT sensors?