How do you test AFM

[kraia]

I'm pretty sure that my air flow meter is the cause of my problems on my 89' 325i. I can't find anywhere how to test the air flow meter and what values I should be getting. Thanks for any help!!!

 

[Ben]

i dont know where to find the values, maybe in the bently manual. but first off, take it off and see if the flap inside it is moving.......

 

[kraia]

Yeah I did that and it moves fine.

 

[bmwjnky]

What exactly is your problem?

 

[kraia]

The car starts up and then dies. I have a few other threads about that problem, but I've narrowed it down to the possibility of the air flow meter. I'm just trying to find out some info on the sensor. If someone could test a working one even and tell me what they got that would good.

 

[bmwjnky]

It does sound like you have a bad AFM but have you tesed your fuel pressure to make sure you don't have a bad pump?

 

[kraia]

Yeah I checked the fuel pump, and it works great. I'm just trying to find out how to check the Air Flow Meter so that I can be sure that it is broken and also that I have the information for the future. So does anyone know how to test an AFM? Other than replacing it with a known good one.

 

[Rukus]

Take a multimeter on continuity mode and connect it to the terminals on the AFM. I would pop the cover off so you cna see which terminals to connect to , rather than guessing. and connecting to your air temperature sensor terminals .

an AFM is a pontentiometer, meaning its varies voltage output by position. so if you see less continuity with the AFM closed and a more with it open, then i'd say its safe to say your afm is working.

This is only if yours is flap style.

if you have a Mass Air Sensor (wire) then i am not sure how to help you.

 

[bichmgnt]

If it is truly bad you may be able to get a good one on ebay for about $35. I just looked but didn't see any cheap ones. I think there was one for $59 starting bid. I got one recently to have a spare for a big six AFM conversion. Make sure you get the same part number as the old one because I think they have to match to the engine control module.

Steve

 

[Rukus]

i don't think they necessarily need to match up.. but its a good idea to pick one that does!!

 

[ldzpstnr]

They do not need to match up on the 318i's. I put a AFM with a different part number on one of my 318i's and it worked fine.
Rukus you are aboslutely right. The AFM is just a pointmeter and adjusts the voltage as it moves. You can read this with an OHM(?) meter.
I do not think the AFM is your problem. If the AFM is faulty the car will just not start, atleast in my expierence. I think you have another problem. Might be your ECU. I have had ECU go out. The car would start up fine but after about 30 seconds it would start to run real crappy and would not get over 3,000 rpm no matter what I tried. Later

Aaron

 

[ldzpstnr]

If you find out exactly how to test an AFM let me know. I do have a used one in my shop. I think its the same, but it came off a 318i. I just compared my 318i one to my 325 one and they look identical. They have slightly different part numbers though, just the last 3 digits. I think it will still work if it tests ok.

Aaron

 

[Rukus]

jsut nevermind what i was going to type