Sensor Inputs:
i have done some testing using a multimeter and have explored how the sensors change under different conditions. The sensors send vital information to the E.C.U so that the engine can operate can at its optimum performance
Coolant temperature sensor. This sensor tells the computer whether the engine is running cold or warm. if the engine was cold the reading would be a high voltage (3.4v) and if it was warm the voltage would drop (1.0v) this voltage is sent to the computer to tell it whether its cold or warm. The same principal applies to the air temperature sensor except in reverse when cold air is coming in it will read a high voltage and when warm air is coming in it would read a low voltage.
Throttle position sensor. this tells the computer whether you are accelerating or not at idle the sensor will have a low reading (0.627v) and when the throttle is wide open it would read higher (3.9v).
Crank sensor. This tells the computer where the crankshaft is on its rotation through the four stroke cycle. It is measured in hertz or you could measure it in a.c voltage.
Oxygen sensor. This is the sensor that controls the air/fuel mixture. It tells the computer whether it is running rich or lean. It helps the computer to maintain an efficient burn.

Outputs:
Fuel injectors. These are measured in duty (%). if you got a reading of 50%, this means that the injector is being held open and kept closed for an equal amount of time. If you were to be accelerating the injectors would be held open for a longer period of time because the engine requires more fuel.
Spark. Spark is measured in Hz (hertz).

Relationship between inputs and outputs:
If you where to put your foot down on the accelerator the T.P.S voltage would increase. The computer reads this voltage and makes adjustments to how long the fuel injectors are held open to get adequate amount of fuel into the cylinder.
The oxygen sensors gives a voltage to the computer. The computer reads the voltage and depending on circumstances will adjust the injectors to be held open or closed for a longer period of time. The oxygen sensor is constantly giving a different voltage because its is trying to achieve a mixture as close to stoichiometric as possible.

Closed Loop fuel Control:
Closed loop fuel control means that the computer relies on the sensors information to achieve best performance. If a oxygen was to go bad, the computer wouldn't know if it was running too rich or lean. This would cause bad fuel economy as excessive fuel is not being burnt. If the coolant sensor was broken the computer wouldn't pick up that the engine is cold so starting on a cold morning will become a problem as the computer is not holding the injectors open for enough fuel to go into the combustion chamber.