How to test MAF sensor?

[DrScientist]

Hi all. I am having a little trouble out of my 1994 Mustang GT. The engine runs rough and lacks power, and the check engine light is on. So, I scanned for the codes. One of the codes says that the Mass airflow sensor is "Below minimum voltage". So I wanted to know how I can check to see if the problem is a dead sensor.

If not, then the problem is obviously going to be somewhere else.. in the wiring. So I need to be able to test the MAF sensor itself, just to be sure. Because those sensors are a little expensive to replace. But the sensor itself has 4 pins, and I don't know which ones to check with my voltmeter/ohmmeter. And I can not seem to find the information anywhere, regarding the proper voltage/resistance that I should be reading from it. So I was hoping someone here could tell me these things. Anyway, thanks for reading!

 

[toyman]

There are 4 wires. Battery voltage, ground, PCM power ground and signal. The signal volts will be between .2v - 1.5v at idle. Since you can't simulate the volts at 60 mph just increase the rpms and you should see an increase in volts. If the PCM is showing a code that is most likely correct. Chances are you have a 16 year old sensor and like most electronic sensors they degrade over time. Looking at it from the harness side the connector has an 8 pin configuration. The active pins are on only one end. 2 on the left and 2 on the right. The pin second down from the top left side is the signal wire. You can also disconnect the connector and back probe the signal wire. If the wire is broken there will be infinite resistance (open circuit).

 

[DrScientist]

Ok thank you sir. I will test that tomorrow and see how it turns out.

But now I would like to ask you a question about the IAT (intake air temperature) sensor. I actually did test it today, and it was within the proper resistance spec. It was 90 degrees Fahrenheit outside today, and so the sensor needed to read somewhere real close to 20kohms of resistance. It did. So that means that the sensor is still good, right? If so, what should I do now? Test the plug... but for what voltage?

Perhaps it is different than the voltage that you suggested to test for the MAF sensor?

 

[toyman]

To test the IAT disconnect and turn the key to on. The reference voltage should be 5v. When measuring resistance across the sensor the resistance is HIGH when the temps are LOW. You could apply heat with a hair dryer to see if the resistance falls as the sensor is warmed. I don't know what the actual readings are but the 5v reference is critical. That signal is coming from the PCM so if it's not 5v you need to check that circuit back.

 

[DrScientist]

Ok thanks. So can this sensor (or trouble related to it) make the car run like hammered crap?

 

[Adam95GT]

yes

 

[toyman]

Yes, both the MAF and IAT sensors are critical. The MAF signal tells the computer how much fuel is need for the volume of air flowing to the intake and the AIT signal is used to calculate the air density which also determines the amount of fuel needed to maintain the programmed AFR. These calculations will also affect how the PCM adjusts the timing.

 

[DrScientist]

Thanks again. Turns out the car is getting no voltage to either of those sensors. Guess I get to have fun tracing down a wire breakage. Whee!

 

[Adam95GT]

They are both attached at the same bulk connector. Start there.