The AFM

[moots]

What is it that determines the amount of fuel delivery ie injector open cycle in our cars....is it the flap in the AFM (the 'hot wire' in the MAF sensor?)
I have the AFM.I adjusted(increased)the AFM tension by one notch hoping I would reduce the fuel consumption but no....no change. :(
Can someone enlighten me?

[MarkD]

What is it that determines the amount of fuel delivery ie injector open cycle in our cars....is it the flap in the AFM (the 'hot wire' in the MAF sensor?)
I have the AFM.I adjusted(increased)the AFM tension by one notch hoping I would reduce the fuel consumption but no....no change. :(
Can someone enlighten me?


I wouldn't suggest changing the tension on the AFM. You will be changing the a/f ratio at wide open throttle, but not at part throttle as the the O2 sensor is used as feedback during PT and will try to keep the a/f ratio near stoichiometric. At WOT, you want a slightly rich mixture. There are products available that increase your fuel economy as well as performance.

Mark

[George M]

since an engine really can't control how much air is ingested however can monitor air flow via AFM, the end result being amount of fuel is controlled via injector duty cycle (given a particular injector size/flowrate) relative to "measured but not controlled amount of air" via AFM...which is just that...a meter that measures air flow. If you change the door flap position versus resistance curve input to the DME, you don't accomplish very much for two reasons....1) The O2 sensor knows the score on combustion by measuring air/fuel after combustion, providing this information back to the DME which in turn adjusts injector duty cycle to strike a better balance between fuel and air....and 2) The DME is adaptive, so overtime a small tweak to the AFM to change its calibration will get absorbed by the O2 sensor adjusting amount of fuel. A more effective bandaid...or home spun chip if you will...that I also don't support, is adding a resistor to the temp sensor to dupe the DME into thinking the engine is running too lean or too cold which in turn would richen the air/fuel....as cold engines require less air (choke) or proportionately more fuel...which can be achieved with a fuel injected car by increasing injector duty cycle. In this case, again the O2 sensor detects exhaust temp and tells the DME the score but the DME's adaptive norm for optimum air/fuel is adjusted toward more rich based upon the temp sensor input that the engine is running colder via the resistor than it actually is.
Personally, I wouldn't change the AFM calibration or add a resistor however would and have adjusted the idle mixture screw on the bottom of the AFM which is set lean at the factory biased toward meeting emission standards.
HTH,
George

[moots]

Thanks Mark and George.I failed to state that my car has got no O2 sensor so that sorta throw all explanations out the window don't it.Nonetheless,your feedback gave me new insights of how things work.

[winfred]

in the quest for better mileage, i would look at retro fitting a 02 sensor and just stay away from leaded gas, i've never done this but have herd about people doing it, i cleaned the contacts in my afm on my 535 and got a small boost in mileage and performance, i agree with mark totally on not playing with the spring tension, unless you have done some mods to the engine that require a lot more air and a fuel mixture adjustment leave it alone, it always helps to have a good tune up for max econmy