Difference between air flow meters

[HairyScreech]

I know the 320 and 325 meters are supposed to be different but what is the actual difference?

[AardHawk]

Assuming that they are both sending the same format signals, then its the spring setting.

[Speedtouch]

Could be a difference in the value of the resistance of the carbon track.

[AardHawk]

The reference voltage differs between early and late. 12V as opposed to later 5V. The voltage curve shape also differs. Considering that the same size meter is used for M20B0 and M30B28 and all engines in between, then year for year and ljet v motronic its got to be the spring setting.

In the dim past I have recalibrated M20b20 meters to run on M30B28 ljet engines by tweaking the spring.

[Brianmoooore]

The thick film carbon tracks that form the resistance element of the potentiometer at the heart of a AFM are far from linear, and are individually tailored to suit the various engines.

[AardHawk]

Brian do you have definitive proof that that is true or is that supposition.

[Speedtouch]

Bosch laser-calibrated the AFMs to suit each different engine:

http://www.r3vlimited.com/board/showthread.php?t=218428

And the resistance value changes:

http://forums.bimmerforums.com/forum/sh ... Adjustment

[HairyScreech]

^^ that corroborates other info I have had.

Not sure if my AFM is a bit moody, resistances check out ok and voltages vary correctly. It just seems a bit off around 5k.

Might press on with the M3.3.1 upgrade instead of getting a new AFM. Not been anywhere near it for ages due to a new job.

[AardHawk]

Speedtouch I dont believe either of those pages are saying that the AFM is laser calibrated for each type of engine. Quite the opposite in fact.

I understand the term "laser Calibration" to mean that the resistance of each segment is "adjusted" to produce a smooth curve (early) and line (later) when graphed out.

I do note that various boards do have different numbers on them however.

[HairyScreech]

I have both sitting around at the moment, Admittedly one with a grumpy spot.

I will measure both tonight if it is not pouring with rain and report back.