IAT sensor testing, Renix 4.0

1989 Renix 4.0

Just wanted to throw this on here so it might help someone in the future during their troubleshooting.

My IAT would test just fine when on the rig. I would take a reading and the resistance was about right according to temp / resistance charts I have found online.

I went ahead and pulled it, hooked up my VOM to it and put my heat gun to it.

As it warmed up it would VERY slowly decrease in resistance but would max out ~1.4k ohms and would not go ANY lower.

I had a used one so I did the same exact test with it and the resistance on it would drop MUCH faster than my old IAT would and it kept right on going past 1.4k ohms. I stopped heating it up once it passed 300 ohms.

I guess the moral to my story is just because your static test looks ok does not mean the sensor is ok.

I have a couple quick, crappy videos I will attach later to illustrate my point.

I will be doing this same test on the ECT sensor in the near future also.

1st video is the old sensor. Notice how it hits about 1400 ohms and just kinda stops and is very slow getting there.

2nd video is the new sensor, notice how fast the resistance drops.

Both tests were done with the same heat gun, same temp, same distance from sensor and repeated a few times to make sure it was consistent.

EDIT: WOW I really need to learn how to do videos or edit them. Sorry but they do get the point across.


http://vid80.photobucket.com/albums/j193/firehawk618/Cars/1989 Cherokee/Old sensor_zps2axkbitn.mp4




http://vid80.photobucket.com/albums/j193/firehawk618/Cars/1989 Cherokee/New sensor_zps6vtemcb7.mp4

Note from DJ
Thanks for the information firehawk618.

I’m including this information for those that might want to check out there’s.

Information from: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm
TEMPERATURE-TO-RESISTANCE VALUE for Renix
Manifold Air Temperature Sensor (MAT) and
Coolant Temperature Sensor (CTS)
Fahrenheit—Celsius—------Ohms
212*-----------100*--------------185
160*------------ 71*------------- 450
100*------------ 38*-----------1,600
70*------------ 21*-----------3,400
40*------------- 4*----------- 7,500
20* -------------7* ---------13,500
0* -------------18*---------25,000
-40*------------- 40*-------100,700

That is the chart I was using to estimate the effectiveness of my IAT.

Even without the chart one could tell mine was bad.

It seems to have made ZERO difference in driveability so far with the good IAT in there.

Go figure lol.