How to test M42 air flow meter?

[Sergey]

Hi All,

I've recently ran into what I think is an error in Bentley and would like your input.

My car is a '95 318ti, 196K miles. One day my engine would start but wouldn't stay running. There was a CEL , the code was 1225; according to Bentley, air flow meter. The real problem ended up to be something else, but I've run into a puzzle trying to fix it.

I followed Bentley and measured resistance across pins 1 and 2, with ignition off, while moving the 'door' inside the meter. Resistance measured at 11.54 kOhms, but did not change as I moved the meter's door.

I assumed my meter was shot and visited two local junk yards looking for a replacement. I took my multimeter with me and tested the meters the junk yards had. They all behaved the same way: constant resistance. I still bought one of them just in case.

In the end, once I've corrected the real problem and made the engine run, I tried it with both meters installed on the car - the original one and the one from the junk yard - and the engine ran fine with either of them. CEL went off.

I also tried to test the original meter on the car with ignition on and read a continuity that didn't change as I moved the meter's door.

I'm pretty sure the multimeter is OK. I tested the throttle position sensor with it and saw the resistance change, spot on within the range Bentley gives for it.

So at this point I'm wondering if I was testing the meters incorrectly or if there's an error in Bentley or what the deal is here. Does somebody know how to test the air flow meter properly?

Regards,
Sergey.
__________________
'95 318ti 196K

[bmwman91]

Yes you were testing them wrong.  You want to test between pins 1 & 2 OR pins 2 & 5.  Good luck!  Often the real problem is a vacuum leak.

[Sergey]

Just re-tested. 1 & 2 - 11.5 kOhm, no change. 5 & 2 - 10.9 kOhm, no change.
I just find it improbable that of 3 meters that I tested all were shot. Can be, of course.

Do you know normal resistance ranges?

Thanks a lot,
Sergey.

[haledj]

I dont have an answer but I think my AFM is fubar as well.

for more info on your car visit http://www.318ti.org

[Sergey]

Yeah, I'm a member on 318ti.org, no answer there

Regards,
Sergey.

[bmwman91]

Well, that being the case I would have to say the AFM is shot to hell.  The AFM PN for the E30 and E36 is the same, so the wiring diagram I used to successfully test my AFM should apply to yours as well.  I have a spare if ya need one!