MAF and AFM

[t_marat]

What is the difference between MAF and AFM?

[ArtemLepilov]

Mass Air Flow meter and Air Flow Meter, I know the MAF is more expensive. I am not 100% sure, but I can make an educated guess that a mass air flow sensor measures the amount of the air that passes through the airbox in general and the AFM measures the amount of air passing through the box at a given moment.

AFM has a movable plate that opens farther the more air passes through it, opening the plate and increasing the resistance in the potentiometer built into it, sending an immediate signal to the computer, when the MAF is some sort of an integrated circuit that reacts to air AFAIK

I think M50s have the MAF sensors


-Artem

[t_marat]

The Bentley manual says its a heated wire (or a plate), for which it is apriory known what current is required to keep it at a certain temperature. As air passes it cools the wire, thus requiring additional current to keep it at a specified temp; that additional current is indicative of the air flow.

What I wanted to know was the difference between MAF and AFM. So the only difference is MAF is on M50s and AFM is on M30 and other engines?

[ArtemLepilov]

They probably use a slightly different system then... If they are different anyway, its not that the different engines use them... The M30 and M20 use a Motronic 1.3 computer, when the M50 uses an updated Motronic 3.1, etc etc

-Artem

[bill g]

Most common terminology seems to be -
AFM is air flow meter - measures volume airflow by means of a moving door (or vane or flap) which operates a potentiometer as Artem said. Because it only measures volume it needs and has an air temp sensor also. These meters are old technology and are usually more restrictive to air flow than the MAF.
MAF is mass airflow sensor, uses temp change in hot wire to measure air massflow. Because it measures mass it needs no air temp sensor.

Both types of meters, at least as used on BMWs up to mid 90s, are load sensors ie, they advise the ECU of the engine load from which fuel mixture and ignition timing are determined. People often forget about the ignition timing function.

The two types of meter have different output signal characteristics and are not easily interrchangeable.

Bill G Melbourne Aus