View Full Version : IAT sensor question
Hindsight
12-13-2014, 08:40 AM
Quick question on IATS: I'm trying to figure out how many places I'm going to need to tap my intake manifold while it's off the car. I want to run a dual zone IAT gauge and also want the option of running my ECU in speed density mode. The IAT gauge I've been looking at uses the common GM sensor, and I know that is the same sensor that a lot of people run for speed density. My question is: Can I use a single IAT sensor to serve both the ECU and the gauge?
JeromeS13
12-13-2014, 03:10 PM
You should be able to. I have a single GM sensor feeding the ECU and my AimSport Pista gauge cluster.
Hindsight
12-13-2014, 05:59 PM
Nice thank you!
While on this subject, does anyone know how accurate the Accessport IATs are?
Hindsight
12-13-2014, 06:36 PM
I would guess very accurate - pre-turbo though. That's here the sensor is - in the MAF housing. So pretty pointless IMHO.
xxguitarist
12-14-2014, 12:27 AM
One thing- careful with connections. I'm not sure about the supply voltage for the sensor from each ECU and gauge. If they aren't straight 12v (not sure?), but say 5v, and one is a little more 5 than the other, you could have current flowing back through the lazy regulator. Not good.
Other side, if you're using one regulator for the sensor, the proportional reading on the other could be off. If it's all 12v, then feel free to ignore!
We will probably be setting up a datalogger at some point, running parallel off our gauge sensors. I'll cross that bridge then.
JeromeS13
12-14-2014, 11:44 AM
While on this subject, does anyone know how accurate the Accessport IATs are?
It depends on which sensor you use, as well as the location of that sensor. In stock form, not very accurate at all. If you switch to a GM/AEM sensor to after the intercooler and switch to Speed Density, it should be pretty accurate.
One thing- careful with connections. I'm not sure about the supply voltage for the sensor from each ECU and gauge. If they aren't straight 12v (not sure?), but say 5v, and one is a little more 5 than the other, you could have current flowing back through the lazy regulator. Not good.
Other side, if you're using one regulator for the sensor, the proportional reading on the other could be off. If it's all 12v, then feel free to ignore!
We will probably be setting up a datalogger at some point, running parallel off our gauge sensors. I'll cross that bridge then.
The ECU uses a 5v signal to run through the sensor.
ssssly
12-14-2014, 12:21 PM
Easiest solution to this is get a gauge that is set up for data logging like the AEMs. They have their own 5v out that mirrors the input signal.
And IAT is not something that you need to measure so closely that voltage drop or resistive changes from multiple connections is really that big of a concern. The thermocouple itself isn't that sensitive.
Bob_n_Cincy
12-14-2014, 12:49 PM
Quick question on IATS: I'm trying to figure out how many places I'm going to need to tap my intake manifold while it's off the car. I want to run a dual zone IAT gauge and also want the option of running my ECU in speed density mode. The IAT gauge I've been looking at uses the common GM sensor, and I know that is the same sensor that a lot of people run for speed density. My question is: Can I use a single IAT sensor to serve both the ECU and the gauge?
I believe the factory IAT and ECT devices are thermistor type devices. They change resistance based on temperature.
The analog input into the ECU sets up a resistor divider circuit. Typically a 10k ohm load.
Putting 2 measuring device on one sensor would make the measurement by the ECU inaccurate by a lot.
The best way to do this would be to add a second sensor.
Bob
(Electrical Engineer hat on today)
Hindsight
12-14-2014, 03:36 PM
Thanks Bob - I guess I need to get busy with the 3/8" NPT because I'm going to need three of them: One for the ECU, one for pre-intercooler, and one for post-intercooler.
ssssly
12-14-2014, 06:35 PM
The stock system pulls IAT from the MAF sensor on USDM cars.
If you go to the Cobb site, they have a primer for running speed density tunes on Subarus. Is pretty thorough and has the wiring info.
https://static.cobbtuning.com/cobbtuningweb/site/support/accesstuner/help_guides/2.0L_Speed_Density_Guide.pdf
If you have a gauge that works for logging, you could run from the sensor to the gauge and the run the logging wire from the gauge out into the ECU.