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      09-28-2006, 01:36 PM   #59

Drives: X1, 335i
Join Date: Sep 2006
Location: SF Bay, CA

iTrader: (0)

Originally Posted by petesamprs
Can you explain this a bit more? I don't know much about how ECUs work but I'm curious how you are able to trick the ECU into thinking everything's stock when its not.
Well that's the secret part, right?

J/k.. let's break down things a bit.

Boost Target: The factory ECU reads this by reading off a T-MAP sensor. The Xede intercepts that signal and adjusts it as a function of RPM and Load. Now the car sees a revised boost signal and dials the boost up or down to compensate. New targets are reached based upon the massaged T-MAP sensor response curve. ECU is happy. The stock ECU still controls all its atmospheric/temp/etc,. compensations.

Timing Changes: The factor ECU figures out when to fire the spark plug based upon crank position (in degrees) and a corresponding value in the timing map (function of engine load/T-MAP and RPM). We don't want to change the map in the ECU since that will be stored and logged. So we intercept the crank position sensor signal and shift it in time (either delay it or advance it). This time shift will make spark timing shift as well. The stock ECU does not know that we are doing this. And it is happy to go about doing what it suppsed to do. Furthermore, the stock knock control system still functions and ready to do its thing when conditions take a turn for the worse (bad tank of gas, super hot conditions, etc,.)

Fueling Changes: The stock computer delivers fuel based upon two things (actually more but these two are the major variables): The raw fuel map and AFR sensor signals. The raw fuel map looks at engine load/T-MAP (we we already modify.. hint hint) and RPM to determine where on the table the engine is operating at. At this point, it tells the fuel injectors to spit out X amount of fuel. Then it reads the data from constantly working wideband o2 sensors. The signals tell the computer if they need to add or subtract more fuel to achieve the desired AFR target. This constant feedback loop goes on and on and on. We dont want to change the actual mapping in the ECU. That would be evasive and easily loggable. Instead, the XEDE intercepts the wideband signals and adjusts them as a function of T-MAP and RPM. The new "adjusted" data is sent to the ECU and it makes the necessary enleanments/enrichments. The end result is that we get the fueling we want and the stock ECU is happy, thinking that it is doing its usual job. The stock ECU still controll all its long and short term adaptive fuel trims just like it would in a stock car.

Those are the basics. There's some other stuff invovled as well. But we can't disclose everything for obvious reasons For example, how do we make it so the closed loop fuel control corrections are instantaneous? Or why do we include a 3rd boost control solenoid to control boost? Or why do we recalibrate both MAP sensors and not just the one used to control fuel? The list goes on and on. But there are reasons for everything. I wouldn't want to mess up my own personal car, now would i?