i m still thinking reading bout the maf conversion..i was just wondering why cant we use a maf which give the out put 0-5volts instead?
like this one here http://www.ebay.com.au/itm/BMW-Air-Flow-Mass-Meter-Sensor-MAF-E46-318i-318ti-316i-316ti-0280218075-/261196365638
thank u
Just about all automotive sensors operate on a 0-5V range. The issue is getting the right transfer function (look up the term). The ECU expects a very specific voltage-vs-airflow relationship, which is specific to the stock AFM part. On top of that, a MAF's output is proportional to mass flow rate (kg/hr) but the stock AFM's output is proportional to volume flow rate (m^3/hr). Assuming barometric changes are minimal (altitude), the two are related through air temperature. Conceivably you can hook up a MAF to the stock ECU/chip and it will run just fine at ONE temperature. Once air temp shifts by more than 10 degrees Celsius, the ECU will not be getting the right information from the MAF anymore and your mixture will start to get a little lean/rich. You could stick a fixed value resistor onto the ECU's air temp sensor pins and fool it into thinking that it is a constant temperature outside which would bypass that issue, but you may have knock problems on hot days since the ECU does retard ignition timing when the air is very hot. And of course, I do not know of any MAF with a transfer function that matches the stock AFM's transfer function at any normal temperature. I went through all of this in 2005 when I developed my first converter and the "temperature fooling" method doesn't work well.
ALL of the above ignores the fact that the M42 has some pretty heavy resonances in the intake/air box, and a MAF is so sensitive that it will have very large output voltage swings during these resonant modes that the ECU cannot properly read. The signal swings are bad enough that the ECU will stop injecting fuel under 100% throttle conditions from 2300-3000RPM. Using a cone air filter helps by eliminating the cavity resonances in the stock air box, but the stock air box really is best and chances are that you will lose power from using a cone filter.
I really do apologize for letting this project die. After I got my last set of prototypes together, I realized that there were some things that I didn't like about how I designed it, and while it worked, I just wasn't comfortable selling it without correcting some things. Too much of an engineer here I guess, but I don't want to commit to taking people's money for something that I know has little issues. The project has been under part-time development again, and the next rev should be better than the last one...it's all a big learning experience. Working on my house still takes priority (happy wife = happy life lol), but the next revision of the MAF converter is seeing some development at least.
