Multi-port Fuel injection:
Gradually, as new engines were designed, throttle body fuel injection was replaced by multi-port fuel injection(also known as port, multi-point or sequential fuel injection). These systems have a fuel injector for each cylinder, usually located so that they spray right at the intake valve. These systems provide more accurate fuel metering and quicker response. In this system, fuel is pumped by the electronic fuel pump at about 30-55psi through the fuel filter to the fuel rail. The fuel pressure regulator sits at the end of the fuel rail, its job is to adjust fuel pressure in the fuel rail. The injectors sit between the fuel rail and the intake manifold/runners. When the injectors are opened by the PCM, pressurised fuel is prayed into the intake manifold/runners. This is done during a cylinders intake stroke to pull fuel and air into the engine. MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke; batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke; or simultaneous, in which fuel is injected at the same time to all the cylinders. The fuel that the fuel pressure regulator allows through to control rail pressure is returned to the tank through the return line. Mutli-port fuel injection is the most common fuel injection system on the road today.