Is there a way to test the ACT and ECT sensors?

[The Shape]

My engine has been a bit rough at idle lately. The RPM's stay steady at around 650 no surging. I did pull the IAC and the EGR valves and clean them, but that made no difference. I changed the plugs earlier in the spring, Autolite 25's gapped at .054. The plug wires are only about 1 1/2 years old, and the cap and rotor are about 2 years old. I have had this car 3 1/2 years and only put 23K miles on it so I wouldn't expect the plug wires or the cap and rotor to be bad although I haven't ruled them out completely. My first reaction was to just throw a whole tune up at it (plugs, wires cap and rotor) but I don't wanna throw money away when those parts don't have many miles on them.

I did pull my codes and all I get is code 11 all clear. But I know I have read here that things such as the ECT, ACT and O2 sensors can get out of calibration enough to cause problems without throwing a code. So I am looking for any suggestions and wondering if there is a way to test the ACT and ECT with a multimeter. Car seems to run fine it just doesn't want to idle smoothly.

 

[jrichker]

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor. Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the RH front of the engine in the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from the rear. Use care in doing it so that you don't damage the wiring or connector.

Here's the table :

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

 

[The Shape]

Thanks J that is exactly what I needed buddy.

 

[HISSIN50]

JR is the man!
Sometimes just giving the sensor heads/elements a cleaning helps (mine sometimes have hair on them).

Good luck with it James.

 

[The Shape]

Well I forgot to bring a meter home from work this evening so I haven't had a chance to check the sensors yet. I did check my cap and rotor and noticed the rotor tip and the cap contacts had a pretty good coating of carbon. I installed a new cap and rotor it didn't seem to help much but I am sure it didn't hurt. Car seems to still have plenty of power it just idles like it has a bigger than stock cam.