Inertial effects of AFM flap vs. engine performance

[Sagaris]

What are your thoughts about a small hesitation being caused by the AFM flap moving during shifts or hitting bumps? I think it is a possibility, especially with an aftermarket intake setup.

I have just the slightest hesitation when I shift into 2nd below 3k which just makes it feel like I am not operating the clutch very smoothly. if I take it above 3k the shift is smooth because I don't get a slight hesitation when I come back on throttle. I am suspecting that the movement of the AFM flap has something to do with this. However, this is an extremely minor issue and wont be losing any sleep over it in the near future. The average person wouldnt even notice it. The aim of this thread is purely just to gauge whether anyone else has suspected something similar due to the nature of the AFM design.

[digger]

a proper running M20 has no such issues

[paperplane94]

a proper running M20 has no such issues

Yessiree bob!

The Bosch AFM is laser tuned from the factory to match the engine and feed the proper volume and air temp data to the ECU. It should compensate for fluctuations in throttle.

[e30leigh]

it doesnt measure air temp at all. not that ive seen. only air volume/speed. the temp referance for the dme comes from coolant temp sensor. and the tps is the other vital referance. those three are compaired to calculate fuel requirements.

if the afm is dirty the flap can become sticky. its common for them to become stuck partly. it is completely possible that it is sticking and moving on bumps. have you made sure that its clear of oils, dirts, grit or that the flap just isnt catching at all? ive seen them clear and still catch slightly

[digger]

it doesnt measure air temp at all. not that ive seen. only air volume/speed. the temp referance for the dme comes from coolant temp sensor. and the tps is the other vital referance. those three are compaired to calculate fuel requirements.

if the afm is dirty the flap can become sticky. its common for them to become stuck partly. it is completely possible that it is sticking and moving on bumps. have you made sure that its clear of oils, dirts, grit or that the flap just isnt catching at all? ive seen them clear and still catch slightly

there is an air temp sensor in the AFM

[nando]

it doesnt measure air temp at all. not that ive seen. only air volume/speed. the temp referance for the dme comes from coolant temp sensor. and the tps is the other vital referance. those three are compaired to calculate fuel requirements.

yes, yes it does. pins 1 and 4 are for the IAT.

you cannot have a speed/density system with no IAT. it would be like alpha-N with no TPS.

anyway, interial effects of the AFM are extremely small. if you have poor throttle response, there's maintenance issues. perhaps the AFM is gummed up, or a vac leak, or injector not working right, or something else like that.

[paperplane94]

it doesnt measure air temp at all. not that ive seen. only air volume/speed. the temp referance for the dme comes from coolant temp sensor. and the tps is the other vital referance. those three are compaired to calculate fuel requirements.

if the afm is dirty the flap can become sticky. its common for them to become stuck partly. it is completely possible that it is sticking and moving on bumps. have you made sure that its clear of oils, dirts, grit or that the flap just isnt catching at all? ive seen them clear and still catch slightly

That is respectfully wrong, the ECU uses the IAT in the AFM to calculate the Mass of the air. New Mass Airflow sensors do that all in one go and send it to the ecu.

Just peer into a Bosch AFM, you'll see the black thing sticking outin front of the vane. Blow on it and the resistance changes! Its ingenious to me.

[e30leigh]

i shall look into just as you say. i was going on by 2nd hand info. perhaps i am wrong. my bad.

[jlevie]

The first things I'd suspect would be intake leaks, a sticky AFM vane, or a worn spot in the AFM's resistance trace. A smoke test of the intake will tell is there are leaks and where they are.

[bmw325ijohn]

When you did the m42 radiator swap did you just replace the t hose that Whent to resuvior to a straight hose external resistor delete?

[nando]

^ wat?

[Sagaris]

You can PM me for further info about the M42 radiator swap. I replied to your other post in the M42 radiator thread.

[Gregs///M]

Run some electrical tests on your AFM. Being a mechanical engineering, im sure you can handle it. You'll need to replicate and compare your results to the following article.

http://www.iprimus.ca/~trauttf/temp/AFM/

If you have later model AFM your output feedback will be linear. I would probe your feedback with an analog meter and pull the rubber boot off the AFM connector. Then you can have access to the rear of the connector pins.

Any "drop" or "dip" in voltage while opening the flap is a result of a bad resistor strip.

[Earendil]

Hesitation during shifting might also be your throttle position sensor not detecting closed or WOT correctly as you ease off and back onto the throttle. Not the first thing I'd check (see above suggestions) but stupid simple to test with a multi meter and the dme unplugged while sitting in the drivers seat.

[2mAn]

somewhat on topic, what would you guys suggest to use to clean a dirty afm?