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Discussion Starter · #1 ·
This is probably something really simple but I can't figure out what I'm doing wrong on wiring up this Intake Air Temperature Sensor. I have a GM style IAT sensor (link here), fast response type. And I am attempting to wire it up to an ECU Master DET3 piggy back. And use one of the analog inputs as the source for the IAT. My understanding is the way the sensor works is it has a thermostatic resistor that changes resistance very quickly based on temperature. You hook up a reference voltage source of 5V to one pin and a signal wire to the other pin. Then, you read the voltage (or your ECU) across the two pins and it should be less than 5V depending on temperature and therefore resistance.

I tested the internal resistance of the sensor and at room temperature it's about 1.95 K-ohm. I then took my heat gun on low and tested to make sure the resistance goes down as temp goes up and sure enough it responded very quickly and read like 500 ohm. Okay so I know the sensor itself is working.

To wire it up, I ran one wire from a 5V source to one pin of the sensor. The DET3 has a 5V output pin which I'm using for the source. And then another wire to the other sensor pin which should be the signal wire the DET3 reads to determine temperature. It doesn't matter which pin you use for which wire. Then I used my multi-meter to test if the signal voltage changes at all and it's always 4.97V. Which would mean the air temperature would be like 150 degrees Celsius which clearly ambient air temp is not. Of course the negative of the multi-meter is connected to ground. The DET3 software also reads 4.97V for the analog input of the signal wire as well.

Am I missing something?

Thanks
 

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This is probably something really simple but I can't figure out what I'm doing wrong on wiring up this Intake Air Temperature Sensor. I have a GM style IAT sensor (link here), fast response type. And I am attempting to wire it up to an ECU Master DET3 piggy back. And use one of the analog inputs as the source for the IAT. My understanding is the way the sensor works is it has a thermostatic resistor that changes resistance very quickly based on temperature. You hook up a reference voltage source of 5V to one pin and a signal wire to the other pin. Then, you read the voltage (or your ECU) across the two pins and it should be less than 5V depending on temperature and therefore resistance.

I tested the internal resistance of the sensor and at room temperature it's about 1.95 K-ohm. I then took my heat gun on low and tested to make sure the resistance goes down as temp goes up and sure enough it responded very quickly and read like 500 ohm. Okay so I know the sensor itself is working.

To wire it up, I ran one wire from a 5V source to one pin of the sensor. The DET3 has a 5V output pin which I'm using for the source. And then another wire to the other sensor pin which should be the signal wire the DET3 reads to determine temperature. It doesn't matter which pin you use for which wire. Then I used my multi-meter to test if the signal voltage changes at all and it's always 4.97V. Which would mean the air temperature would be like 150 degrees Celsius which clearly ambient air temp is not. Of course the negative of the multi-meter is connected to ground. The DET3 software also reads 4.97V for the analog input of the signal wire as well.

Am I missing something?

Thanks
I believe you got this wrong and need to send a ground to one pin, then the signal in wire to the other which provides a 5v reference internally, and is pulled down and varied by the thermistor.

Not 100%, but just Google "GM Iat Wiring" and look at some pictures, you'll figure it out.
 

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Can the input be set-up to read current mA?
If not, you need another resistor to make your system Voltage readable :
A: 5Volt ref
A: one side of a 500 ohms resistor
B: other side of the 500 ohms resistor
B: ECU input
B: one side of the IAT
C: other side of thw IAT
C: ground.

I don't know exactly sure what value you need, but 500 will allow at least for a 50‰ voltage swing across 0-5V, taking your 500 hot value.
 

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Discussion Starter · #4 · (Edited)
Thank you for the quick replies! Here is a diagram of what I'm working with. So clearly I'm missed connecting one end of the sensor to ground so good call there @Mr_Random

The other pin of the sensor goes to the Analog input on the DET3. The diagram shows the +5V source coming from somewhere else. But the DET3 also has a 5V output so thinking connect +5V and Analog Input together.

Product Rectangle Font Parallel Screenshot


I believe the Rx in the diagram is configured in the DET3 software which is where you were going @RedP85

Rectangle Font Slope Parallel Screenshot


I'll try re-wiring and report back!
 

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Thank you for the quick replies! Here is a diagram of what I'm working with. So clearly I'm missed connecting one end of the sensor to ground so good call there @Mr_Random

The other pin of the sensor goes to the Analog input on the DET3. The diagram shows the +5V source coming from somewhere else. But the DET3 also has a 5V output so thinking connect +5V and Analog Input together.

View attachment 20682

I believe the Rx in the diagram is configured in the DET3 software which is where you were going @RedP85

View attachment 20683

I'll try re-wiring and report back!
I was wrong about the 5v reference being internally supplied, so yes you do need to "pull up" the sensor input via a 2-4k ohm resistor tied to +5v. Red was more accurate but your pictures are better than both our words combined.
 

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Discussion Starter · #6 ·
Unfortunately, I was unsuccessful at my re-wiring. I tried splicing the +5V from the DET3 and IAT signal wire togther. Then groundied the other IAT pin. Still reads 4.97V. Also, tried splicing the +5V, pull up resistor terminal (2Kohm) on the DET3 and signal wire together. Still 4.97V. I'm at a loss on this one. I played around with the DET3 IAT settings and configured the resistance values at three different temps. Didn't make one bit of difference. Maybe I need to connect this to the stock ECU somewhere?

Any other ideas?
 

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Discussion Starter · #7 ·
Here is the pin out of the DET3 I'm working with.

Pin 12 and Pin 16 are connected together and runs to one end of the IAT. Other end of IAT goes to ground. I just spliced into engine harness ground wire and verified I have continuity to metal in the engine bay. Only other thing I could think of is connecting IAT sensor ground to the DET3 device ground? I think they are actually the same grounding point.

Font Parallel Rectangle Document Number
 

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You hook up a reference voltage source of 5V to one pin and a signal wire to the other pin. Then, you read the voltage (or your ECU) across the two pins and it should be less than 5V depending on temperature and therefore resistance.
How are you measuring voltage?
Where is your black/negative probe touching?
Where is your red/positive probe touching?

 

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Not wired correctly..
If your sensor is 1.95 K at room, and used a pull-up of 2 K resistor, you should have read abiut 2.47 V at room temperature.
5V * (1950/(1950+2000))= 2.47
 
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Discussion Starter · #10 ·
For testing, Black/neg probe is ground on the det3 device and red/pos is pin 16 / signal side of IAT sensor. I’m able to probe back of the det3 female connector with it plugged into the det3 device.

I’ve tried probing the sensor side as well with all wires connected of course and key on. Same results.

This must be a software issue in the det3.
 

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For testing, Black/neg probe is ground on the det3 device and red/pos is pin 16 / signal side of IAT sensor. I’m able to probe back of the det3 female connector with it plugged into the det3 device.

I’ve tried probing the sensor side as well with all wires connected of course and key on. Same results.

This must be a software issue in the det3.
To be clear, you mean Pin 19 sensor ground, correct?

Red on 16, Black on 19. Just making sure you didn't use the device ground for either probing or sensor reference, which would throw off our search.
 

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Discussion Starter · #12 ·
I actually was using the device ground for the negative probe. Pin 19 is not connected to anything right now. I thought that was the ground for the Power Outputs in the DET3. Are you saying I should connect Pin 19 to ground somewhere in the cabin and then probe it?
 

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I actually was using the device ground for the negative probe. Pin 19 is not connected to anything right now. I thought that was the ground for the Power Outputs in the DET3. Are you saying I should connect Pin 19 to ground somewhere in the cabin and then probe it?
Well after some research, Pin 19 is irrelevant unless powered outputs are used. I don't think it hurts to give it a ground as well, but otherwise shouldn't affect us.

Earlier you mentioned running the internal 2k pullup along with +5v to the sense side of the IAT, and if it's still connected that way then that is wrong. According to the pinout, the internal pullups are connected to +12v. You need an EXTERNAL 2kohm resistor, tied to +5v with the Iat and sensor input on the other leg.
 

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Discussion Starter · #14 ·
Well I still didn’t get the IAT sensor wired and or configured correctly. Then the car started running really rough and wouldn’t boost at all. All the input corrections were disabled in the DET3 software so essentially it was set up to be a pass through device. I’m not sure what the deal was but I suspect the connector pins were loose and the cps and ignite signals kept dropping. So I decided to just disconnect the whole thing and run complete stock. Now the car runs perfectly. I think it’s best to save for a stand a lone Ecu and go that route. At that point I will build a whole new engine harness from scratch and do it right.

Thanks all for replying and the help. More to come!
 

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Well I still didn’t get the IAT sensor wired and or configured correctly. Then the car started running really rough and wouldn’t boost at all. All the input corrections were disabled in the DET3 software so essentially it was set up to be a pass through device. I’m not sure what the deal was but I suspect the connector pins were loose and the cps and ignite signals kept dropping. So I decided to just disconnect the whole thing and run complete stock. Now the car runs perfectly. I think it’s best to save for a stand a lone Ecu and go that route. At that point I will build a whole new engine harness from scratch and do it right.

Thanks all for replying and the help. More to come!
While i am intrigued by the piggyback, I totally agree that a standalone is the right path! Unless you're adding features, I don't see a need to build a new harness. I overhauled mine with new spring-type ev1 plugs, heat shrink and corrugated loom cover - to the point that it almost didn't fit but I wanted max protection for the 40 year old wires.

Also the standalone makes more sense for a car with OBDII and associated emissions testing, reversible/covert as it is. I don't even know how emissions (testing) works for our old cars other than O2 sensor in the tail pipe... as long as you have a cat you can put whatever computer you want as long as the tune is good.

On that note i've been considering building a speeduino with oe ecu plugs for maximum cheapness and adaptability.
 

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Discussion Starter · #16 ·
While i am intrigued by the piggyback, I totally agree that a standalone is the right path! Unless you're adding features, I don't see a need to build a new harness. I overhauled mine with new spring-type ev1 plugs, heat shrink and corrugated loom cover - to the point that it almost didn't fit but I wanted max protection for the 40 year old wires.

Also the standalone makes more sense for a car with OBDII and associated emissions testing, reversible/covert as it is. I don't even know how emissions (testing) works for our old cars other than O2 sensor in the tail pipe... as long as you have a cat you can put whatever computer you want as long as the tune is good.

On that note i've been considering building a speeduino with oe ecu plugs for maximum cheapness and adaptability.
I don't trust the nearly 40 year wiring anymore. I figure if you're going to spend the money on a stand-a-alone you may as well invest in a new harness as well. My current, stock harness is not horrible. I overhauled it 5 years ago but since then I've spliced into a few times for the DET3 and other misc things. It's time for a new flying lead harness. I do plan to switch to 1zz coil on plugs, and crank and cam sensors in lieu of the stock CPS.

I'll have to look into the speeduino units. I have not heard of them before. Is it sort of like the Megasquirt / Microsquirt DIY type units?
 

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I don't trust the nearly 40 year wiring anymore. I figure if you're going to spend the money on a stand-a-alone you may as well invest in a new harness as well. My current, stock harness is not horrible. I overhauled it 5 years ago but since then I've spliced into a few times for the DET3 and other misc things. It's time for a new flying lead harness. I do plan to switch to 1zz coil on plugs, and crank and cam sensors in lieu of the stock CPS.

I'll have to look into the speeduino units. I have not heard of them before. Is it sort of like the Megasquirt / Microsquirt DIY type units?
My only hangup on installing a full-sync system is the trigger wheel. I wonder how compatible later angle sensing setups could be...

In any case, yes speedy is in the same realm as Mega/microsquirt. It uses arduino as the processor - not considered robust enough for automotive applications by many, but since our ecm is in the dash I see little issue with it. Very DIY and expandable the main positive is the price though...
 

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Discussion Starter · #18 ·
My only hangup on installing a full-sync system is the trigger wheel. I wonder how compatible later angle sensing setups could be...
I have found a couple options. You can get a crank sensor and cam sensor kit from SR-Fab. It's pricey but those guys are pretty reputable in the 7M world. Their kit is on sale right now.

7M CPS delete hall effect kit – SR-Fab

Fornari Racing sells a CPS delete kit too but it requires an ATI aftermarket crank pulley. Not a huge investment but worth considering.

7M CPS Delete Kit – Fornari Racing

@williamb82 please chime in as I think you sell or did a some point trigger wheels. Any other input on options for a full sync setup that deletes the stock CPS?
 

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I sell bolt on 36-1 crank trigger wheels. They will not fit an ATI damper. You must make your own VR sensor mount. Since I am going with an ATI damper on my built 7mgte, I have bought the CPS rebuild kit, and a brand new 4Runner V6 distributor to get the VR sensors from so I can fully rebuild a CPS and see if I can get it to work on the megasquirt. I also bought the magnet mod from Driftmotion though not sure it will help with brand new VR sensors inside the CPS, but worth a shot.


 
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