@SER
Com'n yaar you should have known this, you are my expert here
I think others confused you!
@Jimmy
ECU stands for Engine Control Unit, in most cars it is the most powerful computer in the car. Yes some cars have more then one ECU example auto trannys have an ECU(which is known as Electronic Control Unit), power windows, etc. All the ECU's inturn controlled by one main ECU and it is this ECU which makes the decisions.
The ECU controls the fuel injection system, ignition timing, and the idle speed control system. The ECU also interrupts the operation of the air conditioning and EGR systems, and controls power to the fuel pump (through the control relay). Based on information from the input sensors (engine coolant temperature, barometric pressure, air flow, etc.), the ECU determines optimum settings for the output actuators (injection, idle speed, ignition timing, etc.).