AFM question

[Telf 224 2 Cars]

With my on going refurb I've taken the lid off my AFM and tested it as per the instructions in the injection basics article.

 

I found that when moving the wiper the resistance jumps almost instantly from 200 ohms to about 1K and stays there. Now before I took the car for its lengthy stay in the garage it was running ok.

 

If this fault was there how is it possible that it was running - I thought I understood that the fuel/air mix is set throughout the range by the movement of this arm - ie producing a signal for the ECU relative to air mass.

 

Is it therefore possible to have the mixture screw on the AFM set to allow the car to run with a knackered AFM?

 

Anybody enlighten me?

 

Cheers!
 

[jackherer 543]

Put a reference voltage into it and test the output voltage as per e.g. http://www.clarks-garage.com/shop-manual/elect-22.htm

[DamirGTI 342]

As Kieran said , forget the resistance testing - best to hook up an 9V battery to the AFM and use analogue multimeter for testing .. as you swing the wiper arm observe the multimeter needle , should read smooth/linear without "jumping" if the potentiometer track is good .

 

Or you can fit the AFM in the car , providing all the electrics are connected , turn the ignition ON leave the AFM connected and backprobe the AFM via connector and with the top lid open swing the wiper arm and observe the reading on the multimeter (again , analogue multimeter is best for doing this ..)

 

D

[Telf 224 2 Cars]

to be fair I compared it against a known good one using resistance as a measure and one did show a gradual increase from 150 - 1K Ohm, the other just jumps from 150 almost straight to 1K

 

Ill give it a go with a power source though

[Telf 224 2 Cars]

update:

 

So tested with a 9V battery- flap closed reads 1.3 V and fully open 6.5V

 

smooth all the way up in nice 0.1 volt increments. also this happens with the AFM that appears to jump - its totally fine with a voltage supply attached- who knew!

 

Cheers all