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-   -   I'm pretty sure the IAT1 (Trans Temp) scaling is off. (https://www.jb4tech.com/forums/showthread.php?t=60031)

Odinist 10-29-2019 06:34 AM

I'm pretty sure the IAT1 (Trans Temp) scaling is off.

**EDIT** Title should read IAT2, not 1 **EDIT**

Ambient was 31. I can't imagine my IAT2 temps being 12 degrees colder than ambient.

I've also noticed when it's warm, my IAT2s get way, way higher than possible. A few days ago, I saw my IAT1s climb up into the 90s/low 100s when it was like 75 degrees outside. I checked the temps on the tubing for the CAI and there's no way they were that heat soaked.

When it's roughly in the 50s outside, the temps seem to read about right, so perhaps that's a point in the scaling where it's accurate, but going above or below really seems to throw the temps out of whack.

Terry @ BMS 10-29-2019 11:04 AM

Could be, always best to check scaling on cold starts where car has been sitting hours during various ambient temperatures. If you see a trend there we can always rescale it.

Odinist 10-29-2019 12:12 PM

These screenshots were from this morning, about half a mile after I'd left my house, so completely cold start.

Odinist 10-30-2019 05:02 AM

This morning again, cold start, 35 ambient. IAT2 (Trans Temp) was 26. At a light it would go up to 30, then back down to 26 while cruising.

One thing I've noticed that might give a clue, is the temps like to move in 4s. Like this morning, jumping from 26 to 30 and back. I also noticed once I was on the highway, when I'd get really into boost and let off, the charged air shooting back into the intake tract from the recirculating valve would quickly heat the IAT1 up to 42 (a multiple of 4 from 30), then when I'd start accelerating again and it was sucking in fresh air, it would drop back to 30.

Odinist 10-30-2019 09:38 AM

I've set up an app called Torque Pro on one of my phones. I'll connect that on my drive home from work today, and see how it compares to the data I'm getting from the JB4 Mobile App.

Terry @ BMS 10-30-2019 11:47 AM

OK see how they vary based on different starting temps.

Odinist 10-30-2019 01:16 PM

Okay, so after the drive home, I'm like 99.9% sure the "Trans Temp" and possibly even the "IAT" in the JB4 app is off. The temps from Torque read much, much more like I'd expect. Ambient was 35, and both temps stayed a few degrees above ambient.

I'm about try and see if I can use an OBDII splitter and have both the JB4 and the bluetooth OBDII reader plugged in, so I can have both apps going and compare the number directly.

I'll report back here in a bit.

Odinist 10-30-2019 01:59 PM

Okay, so that didn't work...

The JB4 Mobile picked up just fine, but Torque was throwing weird numbers; I guess it doesn't like having two things reading the OBDII at the same time.

But, what's curious, is after I unplugged them both and tested just on the JB4, the numbers seemed much more in line with what I was seeing with Torque by itself. I wonder if having them both in at the same time somehow "fixed" how it was reading?

I'll keep watching it over the next few days, as we're supposed to be due a warm up over the weekend.

Terry @ BMS 10-30-2019 07:17 PM

No that isn't possible as we just read IAT off a requested OBDII PID. So it should match up. Like I said do testing when engine is cold before starting as the number won't move. Then you can easily compare both. Ideally under different weather conditions so we can see the trend and go from there.

Keep in mind there are several intake temp sensors on the car so make sure you're reading the sensor you think you're reading via Torque and not ambient intake temp or something different.

Odinist 10-31-2019 03:38 AM


Originally Posted by Terry @ BMS (Post )
No that isn't possible as we just read IAT off a requested OBDII PID.


IAT1 (which is POST intercooler) is PID 0168, using the formula B-40.

IAT2 (which is PRE intercooler) is also PID 0168, using the formula C-40.

Terry @ BMS 10-31-2019 09:06 PM

Sounds right

Odinist 06-02-2020 04:47 AM

Hey Terry, just as an update, I still think it's skewed as the temps are higher. Like, once ambient is about 60 degrees or so, it starts getting off. For example, this morning on a completely cold start, the ambient temp was 67. Post-intercooler (IAT) was reading at 71. However Trans Temp (pre-intercooler) was reading 91.

There's no way that's right.

Terry @ BMS 06-02-2020 12:22 PM

OK we'll get back to that at some point and correct it.

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