Central to an EFI system is a computer called the Engine Control Unit
(ECU), which monitors engine operating parameters through various sensors.
The ECU interprets these parameters in order to calculate the
appropriate amount of fuel to be injected, among other tasks, and
controls engine operation by manipulating fuel and/or air flow as well
as other variables. The optimum amount of injected fuel depends on
conditions such as engine and ambient temperatures, engine speed and
workload, and exhaust gas composition.
The electronic fuel injectors are normally closed, and open to inject
pressurized fuel as long as electricity is applied to the injector's
solenoid coil. The duration of this operation, called pulse width, is
proportional to the amount of fuel desired. The electric pulse may be
applied in closely-controlled sequence with the valve events on each
individual cylinder, or in groups of less than the total number of
Since the nature of fuel injection dispenses fuel in discrete amounts,
and since the nature of the 4-stroke-cycle engine has discrete induction
events, the ECU calculates fuel in discrete amounts. In a sequential
system, the injected fuel weight is tailored for each individual induction
event. Every induction event, of every cylinder, of the entire engine,
is a separate fuel mass total, and each injector receives a unique
pulse width based on that cylinder's fuel requirements.
This is proportional to the intake manifold's air pressure/temperature,
which is proportional to throttle position. The amount of air inducted
in each intake event is known as "air-charge", and this can be
determined using many methods.
Pulse width is inversely related to pressure difference across the
injector inlet and outlet. For example, if the fuel line pressure
increases (injector inlet), or the manifold pressure decreases (injector
outlet), a smaller pulse width will admit the same fuel. Fuel injectors
are available in various sizes and spray characteristics as well.
Compensation for these and many other factors are programmed into the
The three elemental ingredients for combustion are fuel, air and
ignition. However, complete combustion can only occur if the air and
fuel is present in exact stoichiometric ratio, which allows all the
carbon and hydrogen from the fuel to combine with all the oxygen in the
air, with no undesirable polluting leftovers. Oxygen sensors monitor the
amount of oxygen in the exhaust, and the ECU uses this information to
adjust the air-to-fuel ratio in real-time.
Electronics Fuel injection
Fuel injection is a system for mix fuel with air in an internal
combustion engine. It has become the first system used in automotive
A fuel injection system is which is a
car parts, designed
and calibrated specifically for the types of fuel it will handle. The
majority of fuel injection systems are for gasoline or diesel
applications. With the advent of electronic fuel injection (EFI), the
diesel and gasoline hardware has become similar. EFI's programmable
firmware has permitted common hardware to be used with multiple
different fuels. For gasoline engines, carburetors were the predominant
method to meter fuel before the widespread use of fuel injection.
However, a wide variety of injection systems have existed since the
earliest usage of the internal combustion engine.
The fuel injector is only a nozzle and a valve "the power to inject the
fuel comes from farther back in the fuel supply, from a pump or a