AFM Problem

[benji471]

Iv been trying to fix my bad starting problem for a while now and i though i would have a look inside the AFM as its pretty much the last thing i havnt changed or check and i found the following to wires from the middle to terminal floating in mid air im quessing they shouldnt be like that.



I also did the resistance test first using the main loom terminals and i got some strange results hance the reason i took the top off. Am i right in saying that it should be a steady increase in resistance as the poteniometer is rotated i.e the flap. When i did this the resistance went up with a few down blips till about half way then begain to drop again this isnt right is it? just wanted to double check before i buy a new AFM.

Many Thanks Ben

[asmith88]

yes the test you did was correct and it should steadily increase, sounds like your afm has had it, however i would check for where them wires could be going first of all.

[benji471]

All i can think is that the plug terminal has been changed as there is some soldered sections on the circuit board but then the length of the wires dont match. I also bent the wires to come in contact with the solder and retested it but i just got more blips as in small drops in resistance then it rising again until after half way when it just drops off again. Me thinks it is buggered.

[asmith88]

so do i

[Brianmoooore]

Change in resistance with door angle isn't linear, but at no point should it drop as the flap opens more.
The correct way to check an AFM is to connect a 6 or 9 volt battery across the terminals that connect to the ends of the track, and monitor the voltage on the slider as the flap opens.

[benji471]

The resistance deffinatly drops and rises over the first half but after that it pretty much drops back to where it started.

The correct way to check an AFM is to connect a 6 or 9 volt battery across the terminals that connect to the ends of the track, and monitor the voltage on the slider as the flap opens.

So i would be using all four of the terminal pins to test it using the volts method, im not sure i totaly folow you as regards which terminal do what.

[Brianmoooore]

Three terminals - the fourth is the intake air temp sensor.
I haven't said which pin numbers, because you haven't said which engine!!

[benji471]

I do appologise facelift 1989 320i engine.

[asmith88]

sorry, i used this on my car before.. obvoiusly was useless

my apologies

[Brianmoooore]

Battery negative and meter negative to pin 4, battery + to pin 3, meter + to pin2.
While you're at it, check the resistance of the IAT by measuring between pins 1 and 4. Should be around 3000 ohms at 10 degrees C.

[benji471]

Thank you very much ill give it a go tomorrow.