AFM questions

[Cobra Jet]

Hey fellas,

I've been searching on here about AFM related issues and I still have not seen what I am really trying to inquire about...

The AFM - can this unit be taken apart to diagnose or clean?  I have removed the top of the aribox assmebly w/ the AFM attached and I did see the eletrical element inside at the one end.

I know this element can be "cleaned" by using Contact cleaner (or other safe cleaner) - but my question is, can the actual AFM box or assembly be taken apart to check for other issues?

Is that huge metal box not serviceable?  Can the actual AFM unit be separated from the metal assembly?

I saw one there were someone mentions seeing "carbon tracks" after "taking apart the AFM" - but I have not seen any threads describing or detailing how to disassemble the AFM unit itself...  Where are these supposed "carbon tracks" and how can I see if mine needs to be throughly cleaned?

I looked inside of the metal housing where the air would pass through, but I don't see any carbon build up or any other build up inside of that part.

What am I missing?

I was also looking to see if there was a method of testing the AFM unit to see if it was functioning properly (proper spec'd OHMS), but I have come across a thread that shows how to test the AFM unit in that manner either...  I have seen the thread where the OHM specs are laid out for the AFM, ICV, TPS, etc etc etc, but no direction as to how to actually test the multi-pin AFM connector or unit for OHMS...

I also read up on the fault code 1215 - which merely states that the AFM could be not functioning properly, that the wire harness to it could be damaged which would give the same code, etc...  I just need a firm confirmation as to how to actually determine that the AFM unit IS definitely bad (non-operational), rather than wondering if it's the wire harness, the actual AFM itself, or something else related to it...

I also wanted to know if the AFM is affected by outside ambient temps - meaning if it's cold or hot, does it operate any differently or are there no operational adjustments/changes when this unit is functioning 100%?



Thanks, it's greatly appreciated!

[bmwman91]

There is not really any way to clean the AFM.  The little element you see hanging down is just the temperature sensor and it should not need cleaning.  The resistive carbon tracks inside don't fail from being dirty, but rather from being worn out.  Some have claimed to have tampered with the swing arm inside to make ti touch the track in a new spot, but I would not bank on it working.

As for which pins are which, refer to the 5th image here:
http://www.m42club.com/forums/showthread.php?t=5098

You want to test the resistance between pins 2 and 5 I believe.  Move the flapper door by hand while testing resistance.  If you see any abrupt changes/spikes in resistance, your carbon track is pooped.

[Cobra Jet]

There is not really any way to clean the AFM.  The little element you see hanging down is just the temperature sensor and it should not need cleaning.  The resistive carbon tracks inside don't fail from being dirty, but rather from being worn out.  Some have claimed to have tampered with the swing arm inside to make ti touch the track in a new spot, but I would not bank on it working.

As for which pins are which, refer to the 5th image here:
http://www.m42club.com/forums/showthread.php?t=5098

You want to test the resistance between pins 2 and 5 I believe.  Move the flapper door by hand while testing resistance.  If you see any abrupt changes/spikes in resistance, your carbon track is pooped.

Thanks for the reply (and if anyone knows more about AFM/MAF M42 stuff, it would be you... LOL)...

Can you just point me in the right direction as to where or how I can see these so called "carbon tracks"?  I'm not sure where or what I should be looking at when I have the air box lid w/ AFM in my hands...

You also mention the little item that is seen inside the AFM - as a "temp sensor" - does this mean the AFM's operation IS dependent on incoming ambient air temps whether hot or cold?  If this little temp sensor is "bad" per say, would this render the AFM as inoperable or failing?

Does the OHM test only test the AFM as far as the functionality of the moving internal "door", or does this also test the small temp sensor as you mentioned in your reply?

[bmwman91]

Thanks for the reply (and if anyone knows more about AFM/MAF M42 stuff, it would be you... LOL)...

Can you just point me in the right direction as to where or how I can see these so called "carbon tracks"?  I'm not sure where or what I should be looking at when I have the air box lid w/ AFM in my hands...

You also mention the little item that is seen inside the AFM - as a "temp sensor" - does this mean the AFM's operation IS dependent on incoming ambient air temps whether hot or cold?  If this little temp sensor is "bad" per say, would this render the AFM as inoperable or failing?

Does the OHM test only test the AFM as far as the functionality of the moving internal "door", or does this also test the small temp sensor as you mentioned in your reply?

To get at the internals, pop the top plastic cover off the AFM (the square part).  you will probably mess it (the cover) up a little doing so.

The ECU most definitely requires ambient temperature inputs.  Due to the nature of the AFM, this is needed for density calculations.  However, even if you chopped it off the car would run more or less fine.  You would get a check engine light (maybe a specific code for the thermistor) and would probably run a little rich, but it would run smooth.

The thermistor's resistance is temperature dependent.  As long as the resistance is more than like 100 Ohms and less than 10 kOhms it is probably fine.  They generally work fine or not at all.  Look at the schematic in the link I posted.  The little resistor with the arrow through it is the thermistor.  Just hook the multimeter up to the "common" connection and the other side of the thermistor.

[romeomike]

I'm in the midst of trying to solve why my M42 won't maintain sufficient idle to prevent stalling. I had the check engine light and the AFM 1215 stomp code, then noticed a small hole either melted or worn through the small run of vacuum hose between the nipples on the underside of the upper intake manifold and the fuel pressure regulator.

Changed out the hose, still have the stalling issue, but the check engine light went out for what that's worth. Given a remanufactured BMW AFM goes for over $600, I'm grateful.