Faulty readings from intake air temp sensor

[Howieau]

Hey

I have a brand new Holden VN V6 air temp sensor installed on my 3SGTE after the intercooler. I purchased this because I have an aftermarket computer that already had the calibration files for the VN V6 sensor. On idle the temps are usually around ambient, in the 20's or 30's but on full boost of about 15psi they only go up around 5 degrees. The highest ive seen is 38* celsius.

The computer I run has a button that when clicked, will show the A/D reading (analogue to digital) it is receiving from the air temp sensor at that moment of being clicked. Using the calibration table, I look up where the number falls into the table and its corresponding temperature. So I removed the air temp sensor from the intercooler pipe and had my mate hold the end directly next to a temp probe I have plugged into a multimeter(which was showing accurately). Using a hairdryer I had my mate heat the air temp sensor up to about 40* watching the multimeter, then I hit the button and it gave me the correct A/D number that corresponds with 40* on the calibration table on the ECU. Then we did 50 - 60 - 70* and they all corresponded properly. I think 50* was a little bit out but that didnt matter. So we reinstalled the air temp sensor and same thing - no temps higher than mid 30s on full boost.

Odd thing is too, when I click the "Read A/D" button on the ECU i was using, sometimes it would show really random numbers like in the 10s of 1000s. For example 35048, 11454. Just random numbers which shouldnt appear because it is only meant to give a value between 0 and 1024.

Any ideas on the incorrect readings and/or spikes? Post intercooler air temps shouldnt be THIS cold should they? I run a big but cheapo FMIC too.

Cheers

[Norbie]

Post-cooler temp of 38 degrees is quite plausible, I don't see the problem?

[DX20VT]

Neither do I.

What is the temp of the day, or ambient temp? Unless your turbo is getting near it's limit those temps sound about right to me.

[Howieau]

I logged a couple of boosted runs and went back and looked at the data and the intake air temps only rose from cruising normally at 34* to full boost through 3 gears it went up to 38*.

I assumed the temps should be much higher on boost. What sort of temps do other people get on here off/on boost?

[Duk]

Your 'big cheapo FMIC' would be acting a big cheapo heatsink . It can absorb a lot of heat energy befor showing a rise in temperature .
If you were able to hold the car flat out for long enough, you'd see an eventual temp rise once the 'cooler got to it's saturation point. The point where it becomes a heat exchanger, being hotter than ambient air and so actually dumping heat to cooling air going thru it, and not just being a big heat absorber.

[thechuckster]

my IAT sensor is also a V6 commode item - I used the fridge and pot of water on the stove to get a calibration curve from 0 to 100 (it's not a linear curve). The sensor is in a steel manifold and right above the engine (e.g. prone to heat soak)

Just going thru some old logs - done during daytime:
stop-start around suburbs - 34-36
stop in heavy traffic - soaks to up 40
back to normal within 3 gear changes
highway: 24-30

random bouncing signals indicate a poor connection or a poor earth - is it earthed atthe same point as all your other sensors (e.g. engine block)?

[Howieau]

Nah its earthed on the bracket of the igniter. The bracket has a coat of black paint over it from factory so I think this may be causing a poor earth, Ill fix that no problems.

I always thought air temps under boost would skyrocket. Ive read some threads on how wrapping your intercooler piping is not good because the ambient temps in your engine bay will always be lower than that of those in your intercooler pipe. I thought my engine bay temps would go passed the 40*s easily so I assumed the intake air temps under boost would be higher.

Thanks for clearing that up though.

[thechuckster]

my logs for drag racing showed a climb of about 1-1.5 degrees per gear change (not much if you think about the heat coming from the dodgy turbo and 11-12psi of boost) with the coolant temps dropping.

but by the time you've come up the return lane, the air temps are back to normal.

THe most heat i get is from idling and free-revving in the staging lane.

after pulling up you feel the outlet side of the FMIC and it's quite cold where as the inlet side is quite warm (my piping is mild steel)