In the MPI system, the injectors are divided into groups, and the injectors in the same group are turned on at the same time. For example, 4-cylinder machine injectors are divided into two groups, each group of two injectors, these two groups of injectors take turns spraying oil, the engine crankshaft every turn there is a group of injectors spraying oil. This system of injectors are connected in parallel, the ECU only on the same group of all the injectors send the same signal, the injectors are in the same time to open and close, the programming is simple to simplify the electronic circuit, but it is for the different conditions of the engine lack of random changes in the function, which will produce the phenomenon of stagnation of oil and gas in the intake manifold.

SFI system, each injector directly connected to the ECU, respectively, it can be precisely done just before the injector intake valve is opened, the injector can be done between the two injection period instantaneous adjustment of the mixture to adapt to the changes in different conditions. Therefore, SFI is the most accurate and ideal way of multi-point electronically controlled fuel injection system, many car engines are currently using this way.