Cylinder Temp Sensor Testing Issue

[mcmccaul]

I trying to resolve a temperature gradient alarm issue on my DF20A and have been testing the cylinder temperature sensor. At about 80 degrees, I am getting a reading of about 8 kOhms instead of the 1.8 to 2.3 shown in the service manual. I purchased a new sensor and am getting the same result. I tested the other circuits and the resistance has been accurate to what the table shows, so I don't think its an issue with my multimeter. I'm just trying to figure out why my result is so different than the manual. I also hooked it up to the SDS and the temperature output seems accurate.

Has anyone else come across this issue when testing the cylinder temperature sensor? Just want to make sure its not the sensor before I return the new one.

[redlowrey]

That reading seem high, but you should be testing it in the engine with it running and watch the change in voltage, that is what the computor is doing. Why are you testing it at 80deg F instead of 80c when the temp gradient and alarm is monitored.

[mcmccaul]

The 80degF was just and example of a reading I took while it wasn't running. I took the sensor off and heated it up in a pot of water and the resistance goes down as the temperature goes up as it should. But, the readings are still much higher than they should be (which should correlate to lower temperature reading). I also tested the air intake temperature sensor and it is reading accurately as shown in the manual. I think I'll try a side by side comparison of the old and new cylinder sensor in the pot of water to see if there are any differences or spikes as they are heated at the same time.

[mcmccaul]

I tested the old and new sensors in a pot of water and checked resistance at 10 degree intervals between 70 and 200 degrees F. I got pretty consistent results between the two - they only varied by about 2%-5%. Resistance is still measuring much higher than the manual states, but seems like both are working fine and the SDS temp output seems right. So, I think I'll focus on other components to solve the temperature gradient issue.

[redlowrey]

Mate the only way to test sensors accurately is with an oscilloscope in circuit with the engine running, especially if you have a spike in voltage a multimeter won't pick it up, the up date time is to slow.
Have you checked the exhaust temp sensor, is the engine running hot when the temp alarm comes on.