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914World.com _ 914World Garage _ Can YOU test this for me?
Posted by: McMark Jan 20 2014, 06:53 PM
I haven't been able to find a good graph of the resistance vs. temp for the stock D-Jet intake air temp sensor (IAT). I've never had very good luck trying to measure it directly (hot oil bath with a multimeter). Has anyone done this? Seen a graph (factory or made by someone)? Or is anyone set up to conduct this type of test with accuracy? I can provide the sensor with a wiring pigtail if so. 
Posted by: nathansnathan Jan 20 2014, 07:21 PM
There used to be a link on pbander's page on d jet troubleshooting, but the links are dead now.
http://members.rennlist.com/pbanders/djetparts.htm
Normal Value(s): 300 ohms @ 68 deg. F, about 100 ohms @ 122 deg. F.
Failure Modes
Open: Makes the mixture somewhat richer. Check with an ohmmeter.
Shorted: Makes the mixture somewhat leaner. Check with an ohmmeter.
Notes: The output of this sensor is used by the ECU to adjust the mixture for the intake air temperature. This is a secondary adjustment and has a small effect on the mixture. The sensor corrects for the decrease in air density with increasing temperature by leaning out the mixture. Disconnecting this sensor has the effect of richening the mixture, a common mechanic's trick.
More: This sensor and the cylinder head temperature sensor are negative-temperature-coefficient (NTC) thermistors. Here's a URL on thermistors and how they work:
http://www.rtie.com/ntc/ntcappln.htm
Here's a URL that describes the manufacturing process:
http://www.ussensor.com/manufacturing.html
Below is a URL to a reference that has two charts showing the resistance vs. temperature relationship for the intake air sensor and the engine temperature sensors used in D-Jetronic. The engine sensor data looks OK (about 2.5K at 68 deg. F), but could be from any sensor. Bosch used the same air temperature sensor on all D-Jetronic cars, regardless of model, so the data should be accurate for the 914's sensor:
http://www.icbm.org/erkson/ttt/engine/fuel_injection/d-jet.html
The charts are about half way down the page.
Posted by: worn Jan 20 2014, 09:02 PM
I haven't been able to find a good graph of the resistance vs. temp for the stock D-Jet intake air temp sensor (IAT). I've never had very good luck trying to measure it directly (hot oil bath with a multimeter). Has anyone done this? Seen a graph (factory or made by someone)? Or is anyone set up to conduct this type of test with accuracy? I can provide the sensor with a wiring pigtail if so.
Sounds like you are doing it correctly. Although i thought the temp range was supposedly among the lowest of our sensors. Trying to get it to talk with engine management?
Dont have one since my car is frozen, but i could it if you want a sort of web average. Should i try one?
Posted by: Dave_Darling Jan 20 2014, 10:10 PM
There used to be a link on pbander's page on d jet troubleshooting, but the links are dead now.
The Internet Wayback Machine to the rescue!!
https://web.archive.org/web/20080916111640/http://www.icbm.org/erkson/ttt/engine/fuel_injection/d-jet.html
--DD
Posted by: McMark Jan 20 2014, 10:35 PM
SWEET! Thanks Dave!
Posted by: nathansnathan Jan 21 2014, 07:59 AM
There used to be a link on pbander's page on d jet troubleshooting, but the links are dead now.
The Internet Wayback Machine to the rescue!!
https://web.archive.org/web/20080916111640/http://www.icbm.org/erkson/ttt/engine/fuel_injection/d-jet.html
--DD
Nice!
Posted by: JamesM Jan 21 2014, 01:52 PM
Mark,
If this is to be used with Megasquirt, it can be done and works well. The only issue to be aware of is that due to the sensor being solid/non insulated, and in direct contact with the plenum which is in direct contact with the case, heat-soak of the sensor can be an issue. This becomes really apparent when you try and re-start a hot car after it has been sitting.
Thankfully the newer MSextra versions have a lot of things you can adjust to compensate for this.
-James
Posted by: McMark Jan 21 2014, 10:55 PM
Thanks for the insight James. 
I'll have to pay attention to what the sensor reads before I start the car under those conditions. 
I've been using them for awhile, but went to confirm my calibration values since I'm writing up some documentation to go with my FI kits and couldn't find wherever I had originally gotten my values.
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