A method for controlling a plurality of injectors installed in the same cylinder of an engine may include determining whether an electrical failure occurred in any of the injectors, and entering a fail-safe mode when an electrical failure has occurred only in one of the plurality of injectors in the same cylinder. In the fail-safe mode, fuel supply to an injector that has experienced an electrical failure is cut off, and the amount of fuel injected into the cylinder by a normally operating injector is increased.

A control device for a fuel injection system includes a CPU which generates a drive signal for instructing execution of compression by a fuel pump; a fuel pump drive circuit which controls application of electric power to a solenoid of the fuel pump based on the drive signal; a boost circuit provided with a capacitor for storing electric power to be used for driving an injector; a charging circuit which leads a current generated when the application of electric power to the solenoid is stopped to the capacitor; and an excess electric power consumption circuit which consumes excess electric power of the capacitor. While fuel injection from the injector is stopped, the CPU counts the number of times the fuel pump is driven and turns off the drive signal so as to stop driving the fuel pump as soon as the drive count has exceeded a predetermined count value.

A method for controlling a plurality of injectors installed in the same cylinder of an engine may include determining whether an electrical failure occurred in any of the injectors, and entering a fail-safe mode when an electrical failure has occurred only in one of the plurality of injectors in the same cylinder. In the fail-safe mode, fuel supply to an injector that has experienced an electrical failure is cut off, and the amount of fuel injected into the cylinder by a normally operating injector is increased.

A diagnostic circuit arranged to measure an electrical characteristic in a drive circuit of a coil of a fluid injector and compare the measured electrical characteristic with another electrical characteristic to determine whether a PN junction is working to discharge electrical energy in the coil of the fluid injector, in particular a selective catalytic reduction dosing injector.