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Old 08-24-2009, 08:34 PM   #1
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Default IAT Calibration / Setting issue / Reads 60 or 215 degrees

Im using the GM open element IAT Kit (from diyautotune) and MS1 v2.2 and my Manifold Air Temperature Gauge (thru megatune) worked fine (for a week) and stopped immediately after I wired in a 2nd fan. Once realizing the new issue I disconnected the 2nd fan to see if that would fix the sensors reading and it did not. I soldered the 2nd fan into the wires that are suppling power/ground to my initial fan so nothing was changed except requiring additional power for 2nd fan.

The Gauge illuminates white in megasquirt (when the ignition is on...as if its getting a signal and recognizing it) but displays 60 degrees. Once the car is warmed up and the radiator fan or fans (tried both) turn on (on their own) the gauge then bounces between 60 and 215 degrees. Causing the car to run very lean:(

I redownloaded and replaced my therm files. In my thermfactor file the sensor logs appear to be reading up to 650 degrees and then logs "Sensor Failure - use 170 degF as default" at the begining and end of the sensor log.

What setting are they referring to default at 170?

I bought another IAT sensor wired it up and got same 60 or 215 temp readings.

I tested the signal between the sensor and where it is soldered into the MAF plug and appears good.

Can signal interference happen gradually? Adding a diode would fix that i assume.

Car now has a check engine light (happened same time as IAT issues begining) ..so im assuming its because the IAT isnt working properly.

When the IAT sensors pigtail is disconnected megatune still sees the sensor.

Im a tard, thanks.

Last edited by wrxnova; 08-29-2009 at 05:18 PM. Reason: added details
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Old 08-25-2009, 12:23 PM   #2
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This is a bit unusual - can you replicate this problem on the Stim?
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Old 08-25-2009, 12:52 PM   #3
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Putting a diode in a sensor line will throw the calibration, since diodes create voltage drop. And I'm pretty sure this is nothing to do with the fans.

It sounds like there's a problem somewhere in the vicinity of R5 / C5 / C6 / D2 / CPU pin 24. If it happens on the stim, then you know it's internal.

You may also have an intermittent short to ground on your IAT signal wire.

Quote:
What setting are they referring to default at 170?
In matfactor.ini, a value which is pinned off-scale at either end (ADC 0, which is a short to ground, or ADC 255, which is an open line) is discarded and substituted with a default value.
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Old 08-26-2009, 09:21 AM   #4
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Quote:
Originally Posted by Matt Cramer View Post
This is a bit unusual - can you replicate this problem on the Stim?
I need to order one unfortunately..

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Originally Posted by Joe Perez View Post

You may also have an intermittent short to ground on your IAT signal wire.
Should I maybe try running the 2 IAT wires directly to my ms' harness? Any way to test for this ground issue? Since the polarity on the sensor doesnt matter would grounding 1 of the wires on the frame possibly help?

I have a oil temp sensor working perfectly (with 1 signal wire) and was thinking about wiring that to my IAT sensor just to see if I get a reading.

Thanks.
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Old 08-26-2009, 09:42 AM   #5
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Worth a shot.
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Old 08-26-2009, 09:06 PM   #6
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Grounded IAT on frame, no change.

Grounded coolant fans on frame, no change.

Guess I really need a stim board...

Any other suggestions I can try till I get one?

Thanks.
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Old 08-29-2009, 03:46 PM   #7
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The IAT sensor is getting no power and seems to be shorted out when the ignition is on and off.

Now when in megatune it sees the sensor even when its unplugged.

ECM blown?
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Old 08-29-2009, 05:05 PM   #8
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sounds like what happened to me when one of my resistors wasn't soldered quite right. Open up your MS and poke at the resistors while the car is on and see if it changes at all.
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Old 08-30-2009, 12:36 PM   #9
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my IAT did the same thing!, run new wires to the sensor straight from the ECU, make sure there is no short, make sure there is no water in the connector on the sensor!
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Old 08-31-2009, 07:13 PM   #10
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Quote:
Originally Posted by TrickerZ View Post
sounds like what happened to me when one of my resistors wasn't soldered quite right. Open up your MS and poke at the resistors while the car is on and see if it changes at all.
There is nothing visibly bad on my MS or ECU. After talking to a few mazda techs today i've been told I would see a burnt spot on my ECU's board if it were fried AND the car would not start at all. The car starts.

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my IAT did the same thing!, run new wires to the sensor straight from the ECU, make sure there is no short, make sure there is no water in the connector on the sensor!
Ive tried wiring directly to the ecu and it made no difference.
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Old 08-31-2009, 07:27 PM   #11
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Ive tried wiring directly to the ecu and it made no difference.

check the connector at the sensor, i had water in mine that was shorting it.
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Old 09-01-2009, 12:07 AM   #12
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Quote:
Originally Posted by wrxnova View Post
There is nothing visibly bad on my MS or ECU. After talking to a few mazda techs today i've been told I would see a burnt spot on my ECU's board if it were fried AND the car would not start at all. The car starts.



Ive tried wiring directly to the ecu and it made no difference.
I'm not talking fried, my resistor wasn't soldered well enough and was only making intermittent contact. It looked perfectly fine.
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Old 09-11-2009, 08:35 PM   #13
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I was able to get my MS to Braineak who tested it with his stimboard. 10 minutes after I dropped it off he thought he figured it out when he realized that the DB37 connectors IAT pin was bent and that made us assume that was my issue as everything appeared good on the stimboard.

Unfortunately, I just tried starting the car up and have the same 60 degree IAT temperature reading until my coolant fans turn on. Once the fans turn on the IAT reading toggles back and forth between 60 and 215.
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Old 09-11-2009, 10:10 PM   #14
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:(

you had to have done something funky to the wiring.

You could try to bring a wire in from the AIT sensor directly to the MS and try attaching it to the orange MS wire and oem ECU only, so the stock wiring gets bypassed. I'm still trying to figure out what you could have done...

What sorta voltage is the AIT sending?
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Old 09-15-2009, 12:29 AM   #15
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I rewired the IAT sensor directly into my boomslang harness.

1 of the wires to the orange IAT wire and the 2nd to the ground attached at pins 2A and 2C.

The sensor appears to work now. When I disconnect the sensor at its pigtail, megatune drops the IAT temp to 56 degrees.

AIT at startup was at 83 degrees and slowly crept to 110 degrees (180 degree coolant temp).

Once the car was warm if I hold the car at 2k RPMs the AIT slowly rises. Is that normal? I know that air flow in a garage isnt good but I did have a fan blowing my grill from the front of my car.

Also im seeing up to 210-215 coolant temp just sitting in my garage... making me wonder if both my temperature readings are correct.
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Old 09-15-2009, 09:45 AM   #16
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make sure those the .inc files are in your project folder's mtcfg folder.

Index of /MS/msq/Therm Files/16L_piggy/hr_10g

sounds like they are off, the best test is to see how close the temps read in the morning, they should both be within 1-2 degrees. then you can sit at idle for 10-15 minutes until you reach 207*F coolant where your fans should then kick on.
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Old 09-15-2009, 10:03 AM   #17
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Quote:
Originally Posted by tyson87 View Post
my IAT did the same thing!, run new wires to the sensor straight from the ECU, make sure there is no short, make sure there is no water in the connector on the sensor!
**** UUUUU!U!U!UU!UU!UU!!

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Old 09-15-2009, 08:14 PM   #18
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Quote:
Originally Posted by tyson87 View Post
**** UUUUU!U!U!UU!UU!UU!!
Well sorrrrrry but this was the 2nd time I tried wiring into my harness. The first time (per your recommendation) i wired into the stock harness (by the ecu...guess I misinterpretted your post) and it didnt change anything. But i appreciate the help.

The 2nd time I wired into my ms boomslang harness and that leaves me where I am now.

Im redownloading my .inc files now to make sure now and I also borrowed a laser thermometer so ill report back later.
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Old 09-16-2009, 12:22 PM   #19
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Replaced .inc files and nothing changed.

I started the car up this morning to see coolant temp of 78 degrees and IAT of 82 degrees. Both were increasing (coolant temp was a lot faster than IAT).

Both fans now turn on at 207 degrees.

I went on a 5 minute drive last night, and my IAT got as high at 155 and coolant as high as 215.

I used a laser thermometer on the radiators core multiple times and the temp is very close to what megatune displays.
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Old 09-16-2009, 12:23 PM   #20
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let me ponder for a moment. you have intercooler? 215 is high for the coolant to get, but if the fan is turning on at an indicated 207*F then I'm assuming it's outputting correctly. temps are fairly closely matched, what was temp out when you read 78-82?
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