Air Flow Sensor Troubleshooting on the M30

[Hector]

First of all, I'm a little out of my game. Went to the BMWe34.net site, and the site looks entirely different now. I wasn't able to log in.

I have an intermittent CHECK ENGINE light. I've been checking the resistance of various connector/terminals outputs for voltage and resistance. While checking the resistance of the air flow vane (flap) with the engine cold per Bently, first it reads 0.56 k-ohms with the vane closed; partially open (about 25%) the resistance peaks at 0.85 k-ohm, and fully open it reads 0.34 k-ohms. Is this normal?

Bently says that the resistance should vary without interruption as the vane is moved. It doesn't state that the resistance should increase continuously.

Any comments?

Thanks

[shogun]

E34.net site is presently under reconstruction, you cannot log in yet till Bruno is ready.

[doogie]

Hi there,

I'm not sure on the exact numbers, but I know that fully open and fully closed are both more than half open, which I was confused with in the first place just like you :)

The main thing is does the resistance vary in a smooth pattern across the range or does it jump to short/ open or anything during the travel suggesting the tracks are messed up?

[pingu]

I'd expect the resistance to steadily either increase (or decrease) as the vane is moved. The fact that yours increases and then decreases suggests to me it's buggered.

[Rus]

You can disassemble the AFS and clean it. I performed this procedure on my 535i when I first got it. It didn't really need it (bentley test gave proper results), but its a very easy job. basically remove the bottom cover on the sensor, clean the tracks with alcohol and move the circuit board slightly to move the wiper to a fresh area of the track. Reseal unit with fresh silicone sealant and test. :) BTW, did you pull the error code from the ECU?

[Hector]

I took the AFM to work, and hook it up to a power supply to see if I can get the thing to work. Nothing happened. Either I didn't give it enough juice or the AFM is dead. I might pursue the disassembly method suggested here.

Thanks again.

[ahlem]

Did you do the stomp test to see what code you get?
Does the check engine light go out when you feather the throttle?

[Jeff N.]

+1 for pulling the codes. That's the first step.

How does the car run otherwise?

I seem to recall that to measure the AFM you need to power it with 5v DC. I wouldn't pull the AFM apart until you pull the codes.

[genphreak]

Don't mess with it. Just get a megasquirt and throw the AFM over the nearest fence, or the Miller MAF kit. They both make a HUGE difference and save you fuel- do some miles and get your money back... w a little extra go all the way!