The Engine Control Unit Explained
An ECU is the computer that runs the engine in all modern day vehicles, with the advent of electronic fuel injection systems, in the early 80's these systems where very primitive they just monitored the revolution of the engine, air flow in to the engine and engine temperature. The ECU then used this information gathered from these sensors to inject the right amount of fuel at the right time. The advantages of fuel injection over a carburettured engine 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 almost every aspect of a modern vehicle, even its own efficiency.
The worse place in the world that you could put a sophisticated piece of electronics is under the bonnet of a car or heavy duty vehicle due to massive vibration, constant heat variations and intense radio interference from the ignition system added to the fact that the manufacturers produce on a huge scale, this causes so many problems and design flaws with modern day ECUs.