MAF Sensor workings

[Andy Cabrera]

I have a 2002 Explorer Sport Trac which I know has a MAF sensor instead of a MAP sensor. Now does this have MAF sensor uses a voltage signal to the vehicles computer or does it have a MAF sensor that uses a frequency signal to the vehicle computer?

 

[EddieS'04]

The maf uses 2 elements. One heated the other reference. As air flow across the element the voltage feedback changes with the volocity. From the cooling of the heated element.

Look at it as a vairible resistance. The varible source is increasing air volocity.

I believe the varible feedback is 1 to 5 vdc.

 

[scott degroot]

There is a voltage difference as airflow increases. What you won't find in manuals, even the Ford workshop manual, is that there is also a change in frequency. It is this very reason that makes it so difficult to diagnose a failing maf on a Ford. You can do voltage checks all day long and everything will de just peachy but still have a bad maf. The easiest way to diag a failed maf on a Ford vehicle is by looking at the baro reading with a scanner. This is a calculated value by the maf that corresponds to altitude. I have never seen a failed maf that gave the correct baro reading.

 

[EddieS'04]

What type of scanner for the baro reading, is needed.

 

[scott degroot]

Obviously a Ford NGS or an IDS depending on the year, MasterTech, Snap-on, Genesis, just about all the big players out there will pull it if you go into the vehicle specific section. I want to say that I have seen the baro reading just going thorugh generic OBD II but I don't remember. I have all OE scanners so I don't bother much with looking at generic data.

 

[EddieS'04]

Wouldit be safe to say. At sea level, you may not have a problem with incorrect Barro. Im just guessing. As a retired instrument tech. I understand your meaninings about this.

Thanks

 

[scott degroot]

For starters the baro reading is expressed in hz on a scantool as opposed to in. hg. The pcm makes this calculation based solely on input from the maf. The baro reading updates upon HARD acceleration only. Sea level = 159 hz and as altitude increases the baro reading will decrease. Everytime that I have ever seen a maf issue on a Ford, and let me tell you it probably has to be close to 1000...seriously, the baro reading will always be lower than what it is supposed to be, or in other words the vehicle will think that it is at a higher elevation than it actually is. More often than not it is just a dirty maf. As far as I know the baro reading will never go higher than 159 hz but then again I have never monitored the baro reading while driving through Death Valley but being that whenever you reset it it never goes higher than 159 hz makes me believe that that is it's limit...Ford didn't intend these vehicles to be driven underwater.



The part about how the baro reading updates is kind of important because in the right situations the vehicle can be driven for a very long time while thinking it is at a different altitude than it actually is. Take for instance grandma and grandpa returning from a trip to the mountains where they have came from an elevation of 5000' and are now at 1500'. Unless grandpa decides to floor the gas for a spell and give grandma a heart attack the baro will not update and now the car is running lean and pinging like crazy cause it thinks it's at 5000' still and is cutting fuel to compensate for thin air.

 

[EddieS'04]

Thanks for the tech info...

Seems as if they should have kept the MAP sensor..to compensate..