IAT's which to believe?
 

Hey guys,
I've converted my C5 GM PCM setup to using a 3 bar MAP, Speed density tune using an IAT sensor before the LS3 throttle body and according to HP scanner when I'm logging a drag race my IAT temps reach max of 237 degrees at the end of the run. Yes I'm using a intercooler Air to air and obviously not very good.... but!

I also am running a before intercooler and after intercooler sensors as well that read onto a digital gauge and the before intercooler sensor says 232 and after intercooler says 140 and both PCM & aftermarket gauge sensors are in the same spot so how can there be this much variance?

I double checked the wiring and everything is good. The tune looks good too, no knock or any issues. BTW this is YSI, E85, ID1700's 1000+ rwhp car.

Any suggestions?

Because you've either the ecu set incorrectly, the wrong sensor, wiring problem etc etc

Is the sensor you're using correct for the ecu you are using ?

I believe so, its GM open element that everyone uses. https://www.diyautotune.com/product/...-with-pigtail/

and here is the sensors the cheap dual sensor gauge uses.
http://prosportgauges.com/instant-air-temp.aspx

I have a hard time believing your IATs are up around 230 post-intercooler. Is it possible you've done some weird wire cross with the 5v source and signal?

What does the temp start at or run a light load?

Do they all read the same before start up

I completely agree with you guys, I don't believe it either, at cold start up the IAT's on dual gauge read the same, not sure what they say on HP log, i'll check that. And as the car warms up the pre IC temps are warmer than post IC temps on dual gauge.

The max I've seen the dual gauge post IC temps are 140 in the 1/4 mile but HP says 237 degrees......

"and here is the sensors the cheap dual sensor gauge uses."
Any temp/voltage scale available for these sensors?

ok to my surprise, when cold all 3 read the same temps, 67 pre 67 post 69 on HP Tuners.
I can't believe though the IAT's are that hot post intercooler though.........

Old geezer, if I understand what your asking, there is just a 12v power, ground, and inputs from both sensors.

temperature sensors are usually only 2 wire.

Where are you getting 12v, ground and signal from ?

yes each temp sensors have 2 wires

My 12v is from a key on source, and ground that runs all my other gauges, only signal there is from the sensors, so I have a total of 6 wires (12+, GND, 1 sensor, 2 sensor)

A solid tip thermocouple or restive type sensor will probably be slower to read than the IAT with exposed element. I'd pull both and hit them with a heat gun or some source of mild heat and see what each read and how fast change is in a given amount of time. You could pull them both and put them close to each other and read them at the same time, see if one reads the temp faster and other other catches up or if they are just plain off, etc.

You can test your sensor with HPT.
Remove it from the intake. Start the scanner.
Dunk the sensor element in a cup of ice water. Should read 32F
Then dunk it in a cup of boiling water. Or as close as you can get to boiling. See what it reads.

I doubt these sensors are spot on.

what intercooler are you runnin? cheap ebay/ way to small will act as a heat soak. and how "cheap" of a gauge setup is it?

intercooler is an A&A brand specific for C5 vettes cuz they are so weird with the airflow coming in from the bottom of car.
The core is 25x6x3.5 or 4" I can't remember

Have you tried unplugging the IAT with the pcm on to make sure it's actually reading the IAT?

no I haven't but I can do that easy enough, thanks!

Unlikely, if they read the same cold.

(add: or were you maybe suggesting some how it is wired incorrectly & reading coolant ?)

This sounds to me like a scalar issue in the transfer function of the high reading sensor.

Without a known transfer function for the "cheapo" sensor, (or is the one reading high a factory sensor?) you will have to resort to making your own table based on a controlled test environment.

Without a known function table you have no idea if the output is reading what it is supposed to at a given controlled temp.

Or try another sensor...

Put the two sensors, in the same tube, side by side and test to see if they read the same.

I do believe they are...