This invention relates to fuel injection systems for internal combustion engines and more particularly to those of the type including an intake-air flow detecting device provided on the intake-air passage or manifold duct of the engine to detect the flow of engine intake air as a value of vacuum pressure, a fuel feed pump arranged on the fuel line interconnecting a fuel injection valve fitted to the intake-air passage on the downstream side of a throttle valve and a fuel tank, and a fuel metering device interposed between the fuel injection nozzle and the fuel feed pump to meter the fuel delivered therefrom in accordance with the value of vacuum pressure transmitted from the intake-air flow detecting device.
In general, fuel injection systems of the type described are advantageous in that they are simple in construction and limited in fabrication cost but have been unsatisfactory in that, with the conventional construction, the vacuum pressure in the intake-air passage can hardly be controlled as expected in accordance with the condition of engine operation and hence the system can only contribute a little to exhaust emissions control and fuel economy.