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Old 11-10-2009, 06:01 AM   #1
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Question Usage of OEM IAT sensor 99-00

Hi,

as my DIYPNP is nearly up and running, I sold my old MS2 to a friend at the German board.

He is N/A at the moment - and doesn't have the GM IAT sensor of course.
Will he really need one - or can he go with the OEM one?
(it's quite hard to source the GM part over here in Germany.)

Does anyone know the correct values for the OEM 99-00 IAT (not the CLT - I know they are in the How to built... thread)

Abe?

Greets and thanks
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Old 11-10-2009, 08:00 AM   #2
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When I ran my MS2, I used the oem IAT as well. Never got round to installing the GM one. It worked fine for me. Besides, that's what DIY does with the PnP versions as well.
The stock sensor is a bit slower, but since he's N/A, that doesn't matter as intake temps won't rise as quickly as they do with a turbo.
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Old 11-10-2009, 08:43 AM   #3
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Hi Frank, do you happen to know the resistance values?

Thanks, Greets
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Old 11-10-2009, 09:25 AM   #4
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Never measured them. I believe I used the same ones as those for the CLT.
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Old 11-10-2009, 02:27 PM   #5
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I know they are on the DIY site, under their new pnp thing. They have sensor values for the OEM part, but I don't know them.

And yes, I wouldn't use that on a turbo application. Intake temps vary on the timescale of a throttle press.
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Old 11-10-2009, 03:10 PM   #6
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Attached. Ignore the bias resistor values, these are the stock values as my MS1 was a parallel install.

Jim
Attached Thumbnails
Usage of OEM IAT sensor 99-00-easytherm.jpg  
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Old 11-11-2009, 02:52 AM   #7
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@Reverant - Thanks a lot.

Mine is an parallel install as well.
Do I have to remove a resistor for the IAT? IIRC I removed R7 for the CLT...

Greets
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Old 11-11-2009, 01:52 PM   #8
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Rev: I know you're a data-intensive kinda guy....

Did you ever check to make sure these were right? I tried a few numbers people told me, and they never worked right on my car. I went as far as slipping a thermocouple under the house in the housing where the temp sensor is.... But I'm getting more interested in trying it again.
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Old 11-11-2009, 04:38 PM   #9
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Quote:
Originally Posted by Zaphod View Post
@Reverant - Thanks a lot.

Mine is an parallel install as well.
Do I have to remove a resistor for the IAT? IIRC I removed R7 for the CLT...

Greets
Yes, you need to remove R4. I suppose that Mazda uses the same bias resistors for both models in their ECUs: 99-00 and 01-05, so try the values above. Power the car from completely cold (leave it overnight) but DONT start it, and check that both the CLT and the IAT are about the same - within -/+2 degrees is fine. If they are, you are golden.

Jim
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Old 11-11-2009, 05:17 PM   #10
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Quote:
Originally Posted by AbeFM View Post
Rev: I know you're a data-intensive kinda guy....

Did you ever check to make sure these were right? I tried a few numbers people told me, and they never worked right on my car. I went as far as slipping a thermocouple under the house in the housing where the temp sensor is.... But I'm getting more interested in trying it again.
I always log my way through what I do, so:

1) Measurements were taken on the 11th of July, 2006, 17:50.
2) Ambient temperature at that time was 30C (86F).
3) I moved the car from the parking lot at work to take it about half a mile away, to a friend's garage, maybe less.
4) With the car parked, I measured the resistance of both sensors, and logged both values against what the OBD-II said.
5) IAT was 1550 Ohms, Vout at the divider was 1.82V. Bias resistor is Rb=1550 * (5-1.82)/1.82 = 1550 * 1.75 = 2713 Ohms
5) CLT was 1330 Ohms, Vout at the divider was 2.31V. Bias resistor is Rb=1330 * (5-2.31)/2.31 = 1330 * 1.165 = 1550 Ohms
6) For the above calculations, the formula is Vout = (Vin*Rt)/(Rb+Rt)
7) Three distinct datasets were taken for each sensor. For coolant, 20C, 40C and 80C. For air temp, 20C, 40C, 65C. Values were 2491, 2177 and 317 for CLT, 2499, 2165 and 498 for IAT.
8) Solving the Steinhart-Hart equation (1/T = A + B(ln(R)) + C(ln(R))^3) for the datasets above, the results are:
CLT: A=1.193449*10^-03 B=2.837733*10^-04 C= 6.840434*10^-09
IAT: A=1.193449*10^-03 B=2.837733*10^-04 C= 6.840434*10^-09 (Surprise, surprise)

I've used the above settings on my parallel MS1 with excellent results. The same sensors are used on 89-95 RX-7s, these same settings I also used on LogWorks with an LMA-2 to read the CLT/IAT on that car and matched the settings as displayed by the Datalogit software of the PowerFC ECU.

Jim

Ps. Yes, they ******* work, noob!
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