Engine Control Unit
An ECU (Engine Control Unit) is an embedded computer that runs the engine in all modern-day vehicles, introduced in the early 1980s with the advent of electronic fuel injection systems, these early systems were primitive, with just a few sensors monitoring the revolution of the engine, air flow and engine temperature. The ECU then used this information to adjust the pulse width of the injectors - increasing or decreasing the amount of fuel delivered to the engine. The advantage of electronically controlled fuel injection over a carburettor was the degree of control that a computer had over fuel delivery, 1000s of times more accurate than that of a carburetor.
In the present day, an ECU is a very powerful control system capable of gathering hundreds of channels of information to control every aspect of the engine, even its own efficiency.
One of the worse places that you could put a sophisticated piece of electronics is under the bonnet of a car, due to vibration, constant heat variations and intense radio interference from the ignition system, added to the fact that the manufacturers must produce on a huge scale, this causes so many problems and design flaws with modern day ECUs.