Engine Control Unit

• In modern cars, fuel injection systems are used to regulate not only the amount of fuel entering the engine, but when it's introduced. In the United States, all cars are required to use fuel injection over traditional carburetors. Fuel injections systems are monitored and controlled by the engine control unit, which determines how much fuel should be used when the accelerator pedal is pressed. The gas pedal actually controls how much air is injected into the engine and the engine control unit increases the amount of fuel injected into the engine to compensate for the additional air.
  
  

Physical Operation

• Fuel injectors are controlled not by electrical current or pressure. Instead, each time the engine's computer system determines that additional fuel should be released, it completes a circuit which energizes an electromagnet. The electromagnet forces the valve open, and fuel flows from the fuel pump into the injector. The fuel is basically a valve body that opens and closes based upon the amount of fuel required by the engine. When more fuel is required, the fuel injector turns the fuel supplied by the fuel pump into an atomized spray and injects it into the engine. The goal is to make a fine spray so that the fuel can burn as efficiently as possible.
  
  The longer the fuel injector remains open, the more fuel that enters the engine. The engine control unit governs how long the fuel injector stays open, and uses a number of sensors to make sure that the fuel is injected most efficiently. The airflow sensor determines how much air enters the engine, and the oxygen sensor measures the amount of oxygen in the exhaust. A pressure sensor measures how much power is being produced by the engine.
  
  

Fuel Injection Types

• There are many types of fuel injection systems. Multi-port fuel injection systems offer multiple chambers, each attached to a cylinder on the engine. Immediately before the valve to the cylinder is opened, the corresponding injector fires. Alternatively, each valve can open simultaneously, injecting fuel into each cylinder at the same time. Throttle body fuel injection was one of the first fuel injection systems to be used, and consisted of a system in which fuel and air were pulled into each cylinder on each stroke by the movement of the cylinder itself. These systems are rarely used today, because they lack the ability to regulate the amount of fuel and air in the mixture, a key factor in the efficiency of modern fuel injection systems.