M20 & M30 AFM Autopsy

[DmcL]

have a few M30 AFM's and one fried so took that apart and decided id take my stock M20 AFM apart also and maybe try messing with swapping the springs around or whatever and see what happens. thought id stick all the bits together and take a pic for anyone who is curious about whats different between the AFM's.




i cant say whether the circuit board is trimmed any different in the M30 AFM vs the board in the M20 AFM as the M30 board in the picture is fried.. the AFM was water damaged which is why i decided to take it apart. the M20 board in the pic above is good tho and i have taken the softer 500 spring from the M20 AFM and installed it in the M30 AFM at the same stock position as it was in the M20 AFM along with installing the M20 board in the M30 AFM. i have another M30 AFM that is standard and the 500 spring in the M30 AFM does make the flap open up easier than the stock M30 AFM's 022 spring.

i suspect the curcuit boards are the same for all intensive purposes and the main difference between the AFM's is the stiffness of the spring. E30 M3 uses an AFM that is the same size as the M30 AFM but is a different part number, i bet its the same as the M30 AFM but has a different spring inside. also FWIW someone showed me a pic of the spring from an E28 M5 AFM which is also the same size as the M30 AFM but the spring is different, looks stiffer than the M30 spring.

so far i know these springs and their respective AFM's:

500 spring = M20 AFM
022 spring = M30 AFM
030 spring = E28 M5 AFM (same size AFM as the M30)

[amok]

Any updates? Boyce any changes to the throttle response or anything else?

[Pdxseth]

I have an m30 afm laying around maybe I will try this let me know how it works


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[Gregs///M]

Bosch laser calibrates each AFM during production. Adjusting the spring rate vs flap opening will no doubt affect the voltage output to the ECM.

Your ECM wants to see a specific voltage input per volume of air flowing into engine. Adjusting or swapping the spring tension would offset the voltage output from the AFM to ECM.

In order to get it back to its factory settings you would also have to use a laser calibration machine that Bosch uses. I assume this machine cost more than a used E30 M3.

[hammertime]

ive got an m30b35 and was wondering how to disassemble my maf to clean the contacts. any write ups?

[DmcL]

just stumbled onto this thread from google.

decided to drag it back up from the dead just to answer questions posted since the last time i looked at the thread.

yes bosch laser trim the boards but no, it will not make a realistic difference swapping them around. the main difference from parts swapping is from the spring wheel.

i have run various setups over the years and various combinations. i found that the M30 AFM with M20 spring wheel required the M20 wheel to be clocked a bit tighter otherwise the M30's flap was too loose and opened much too soon. i dont recall the amount i clocked it but it was not a rediculous amount, maybe something around 5 teeth tighter. i basically had a stock untouched M20 AFM on hand and clocked the M20 spring in the M30 AFM until the spring tension was more or less the same by feel when i pushed on the flap in each. i ran that M30 AFM like that for months with no issues and later compared it to an untouched M30 AFM and found the softer M20 spring once clocked a little tighter allowed for slightly quicker response vs the M30's heavier spring.

as for how the spring and spring tension affects the ECU.. i traced relevant maps in the ECU with my ostrich in tunerpro and basically higher spring tension will hold the ECU at lower load cells in maps for longer while a lower spring tension allows it to move up load cells in maps sooner. also there is a bit of a leaning effect even at WOT when increasing tension and the opposite when decreasing tension. that is not a big problem if you are tuning yourself though as you can adjust tension for best response and trim fuel maps to suit if it throws the AFR's out too much for your liking.