Thermocouple and translator box for AIT signal
#1
Thermocouple and translator box for AIT signal
Since our cars have horrible AIT sensor heat soak issues, on top of having extremely slowly reacting sensors, it seems like there would be a good benefit to have a more accurate, faster reacting system. Many relocate their sensors to an area less prone to heat soaking (away from the UIM). This may help, but doesn't address the real problem IMO.
I did some experimenting tonight and it proved to me that the stock sensor is very sluggish when it comes to registering temp changes. I blew a hair dryer into the primary port of the UIM and kept an eye on the temp and voltage readings from my commander. The temps did go up fast. After blowing compressed air into the port to clear out all the hot air I just blew in there, the sensor dropped only a few degrees. Then took about a minute to return to reading ambient temp. It dropped steadily throughout the minute, but there was no actual change of the temp in the UIM.
So my plan is to use a fast reacting thermocouple, placed in the elbow, wired to a simple circuit translator board. Then the translator sends a 0-5V signal to the ECU.
http://www.simplecircuitboards.com/Thermocouples.html
Output calibration wouldn't be hard at all to figure out. We could just heat the stock sensor up to various temperatures, and log the temperatures as well as the voltages (sensor check screen) via the commander.
The ECU interprets a 0-5V signal. The sensor is a PTC (positive temperature coefficient) type, meaning as temp goes up, so does resistance. So I'm guessing the ECU sends a 5V reference signal, and uses the returned signal as it's temp signal. The stock AIT sensor has a green wire and a brown/black stripe wire. I'm not sure which one is which, but that's not hard to figure out.
So the output from the translator box spliced to whichever wire is the temp signal, and done.
Thoughts?
I did some experimenting tonight and it proved to me that the stock sensor is very sluggish when it comes to registering temp changes. I blew a hair dryer into the primary port of the UIM and kept an eye on the temp and voltage readings from my commander. The temps did go up fast. After blowing compressed air into the port to clear out all the hot air I just blew in there, the sensor dropped only a few degrees. Then took about a minute to return to reading ambient temp. It dropped steadily throughout the minute, but there was no actual change of the temp in the UIM.
So my plan is to use a fast reacting thermocouple, placed in the elbow, wired to a simple circuit translator board. Then the translator sends a 0-5V signal to the ECU.
http://www.simplecircuitboards.com/Thermocouples.html
Output calibration wouldn't be hard at all to figure out. We could just heat the stock sensor up to various temperatures, and log the temperatures as well as the voltages (sensor check screen) via the commander.
The ECU interprets a 0-5V signal. The sensor is a PTC (positive temperature coefficient) type, meaning as temp goes up, so does resistance. So I'm guessing the ECU sends a 5V reference signal, and uses the returned signal as it's temp signal. The stock AIT sensor has a green wire and a brown/black stripe wire. I'm not sure which one is which, but that's not hard to figure out.
So the output from the translator box spliced to whichever wire is the temp signal, and done.
Thoughts?
#4
~17 MPG
iTrader: (2)
The stock AIT sensor is a NTC (Negative temperature coefficient) thermistor: when the temp is high the sensor's resistance is low. When finding the resistance vs temp curve, it's a good idea to keep the sensor at the same temperature for a few minutes to let it stabilize. Here are some numbers from the stock IAT sensor from my car:
Temp (C) / Resistance (ohms)
-10 / 9570
9 / 3960
25 / 2080
40 / 1175
50 / 832
70 / 440
80 / 321
I'd be very interested to learn the temp vs resistance data for other OEM sensors, I've only tested mine.
By the way, the GM IAT sensor has an open element sensor, it's not encased in brass like our OEM one is. It responds much more quickly. I'm not the biggest fan of GM connectors (difficult to de-pin them) but the sensor is pretty good.
-s-
Temp (C) / Resistance (ohms)
-10 / 9570
9 / 3960
25 / 2080
40 / 1175
50 / 832
70 / 440
80 / 321
I'd be very interested to learn the temp vs resistance data for other OEM sensors, I've only tested mine.
By the way, the GM IAT sensor has an open element sensor, it's not encased in brass like our OEM one is. It responds much more quickly. I'm not the biggest fan of GM connectors (difficult to de-pin them) but the sensor is pretty good.
-s-
Last edited by scotty305; 09-26-08 at 03:18 PM.
#5
Mad Man
iTrader: (5)
I have a datalog in this thread comparing the temperature change rates of the stock in the greddy elbow and a GM open element sensor..
https://www.rx7club.com/showthread.p...&highlight=ait
https://www.rx7club.com/showthread.p...&highlight=ait
#7
~17 MPG
iTrader: (2)
Same scale (75-150 F) used for both the GM AIT (green trace) and the OEM sensor (red trace). Pink trace is manifold pressure, blue is RPM. GM sensor is very noisy, it looks like one of the wires was not connected well enough (temp even spikes up to a nonsensically high number later in the datalog, that usually indicates a broken or disconnected wire).
Looks like the GM sensor measures an increase in temperature before the OEM sensor, and it gets up to a higher temperature as well.
The smaller sensing element has less mass, it will heat up more quickly than the larger OEM sensor.
-s-
Last edited by scotty305; 09-27-08 at 12:46 AM.
Trending Topics
#8
Thanks for the data. Very interesting stuff. Did you get the noisy readings figured out?
Seems like the GM sensor works differently than our stock sensor, as others have thought about using the open element sensor as an input to the ECU, but aren't able to. It's a 2 wire sensor, probably also an NTC thermistor, so I'm guessing it's a calibration issue. Maybe this sensor with some kind of translator box would be just as good a setup.
Seems like the GM sensor works differently than our stock sensor, as others have thought about using the open element sensor as an input to the ECU, but aren't able to. It's a 2 wire sensor, probably also an NTC thermistor, so I'm guessing it's a calibration issue. Maybe this sensor with some kind of translator box would be just as good a setup.
#9
Since we use a speed density air measuring system (MAP sensor), knowing the density of the air which changes with temperatures is vital for calculating fuel injection. So with more accurate readings, our ECUs have a better input in which to base fuel.
#10
~17 MPG
iTrader: (2)
Thanks for the data. Very interesting stuff. Did you get the noisy readings figured out?
Seems like the GM sensor works differently than our stock sensor, as others have thought about using the open element sensor as an input to the ECU, but aren't able to. It's a 2 wire sensor, probably also an NTC thermistor, so I'm guessing it's a calibration issue. Maybe this sensor with some kind of translator box would be just as good a setup.
Seems like the GM sensor works differently than our stock sensor, as others have thought about using the open element sensor as an input to the ECU, but aren't able to. It's a 2 wire sensor, probably also an NTC thermistor, so I'm guessing it's a calibration issue. Maybe this sensor with some kind of translator box would be just as good a setup.
With the EMS that I have, changing from the Mazda sensor to a GM sensor is as easy as wiring it in place of the stock sensor and selecting 'GM AIT sensor' from a wizard. If I somehow come across a sensor that isn't in the wizard I can just punch in the voltage vs. temp data myself.
There must be a way to make the GM sensor work with the PFC, because fritts was using a PFC to create the datalog that he posted.
#13
Old School
Join Date: Mar 2001
Location: Baldwin City, KS
Posts: 473
Likes: 0
Received 0 Likes
on
0 Posts
There is a chapter in the Logworks3 Manual that has info on thermistors as commonly used in cars. It's chapter 4.2 "Thermistor Temp Sensor Configuration"...
http://www.innovatemotorsports.com/s...ks3_Manual.pdf
It looks like all that is needed is to add a resistor or replace the resistor (if a smaller resistance is needed) from the circuit to use the GM open element IAT sensor. I hope somebody figures this out and posts the how to as heat soak lean conditions are probably a contributing factor in many blown rotary engines. I may do a little experimenting myself when I find the time. Good luck.
http://www.innovatemotorsports.com/s...ks3_Manual.pdf
It looks like all that is needed is to add a resistor or replace the resistor (if a smaller resistance is needed) from the circuit to use the GM open element IAT sensor. I hope somebody figures this out and posts the how to as heat soak lean conditions are probably a contributing factor in many blown rotary engines. I may do a little experimenting myself when I find the time. Good luck.
#14
Eye In The Sky
iTrader: (2)
Join Date: Feb 2001
Location: In A Disfunctional World
Posts: 7,895
Likes: 0
Received 114 Likes
on
66 Posts
A mentioned, moving the AIT sensor to the IC outlet or TB elbow is the first way to reduce heat soak. It works great on my FMIC outlet.
An overlooked way to improve the stock sensor's reaction time is to carefully remove the black plastic coating on the sensor tip until you reach the light brown colored covering of the sensor.
I posted this a few years back in the PFC forum and it does speed up the responce of the sensor.
An overlooked way to improve the stock sensor's reaction time is to carefully remove the black plastic coating on the sensor tip until you reach the light brown colored covering of the sensor.
I posted this a few years back in the PFC forum and it does speed up the responce of the sensor.
#15
Newbie
iTrader: (9)
Join Date: Feb 2002
Location: MI
Posts: 1,171
Likes: 0
Received 0 Likes
on
0 Posts
Not to say that the stock sensor isn't slow, just kind of musing over any real gains you'll see from a different sensor if placed in the same area...
*subscribed .
#17
Old School
Join Date: Mar 2001
Location: Baldwin City, KS
Posts: 473
Likes: 0
Received 0 Likes
on
0 Posts
A mentioned, moving the AIT sensor to the IC outlet or TB elbow is the first way to reduce heat soak. It works great on my FMIC outlet.
An overlooked way to improve the stock sensor's reaction time is to carefully remove the black plastic coating on the sensor tip until you reach the light brown colored covering of the sensor.
An overlooked way to improve the stock sensor's reaction time is to carefully remove the black plastic coating on the sensor tip until you reach the light brown colored covering of the sensor.
Thread
Thread Starter
Forum
Replies
Last Post
The1Sun
1st Generation Specific (1979-1985)
7
09-18-15 07:13 PM
The1Sun
1st Generation Specific (1979-1985)
0
09-07-15 10:21 PM