Abstract: The invention concerns a device for injecting fuel into a diesel engine using a pulsating flow pump for improving the fuel performance of the engines by controlling the beginning and the end of the injection. It comprises a device (20) controlling the closing and opening of the nozzle needle (5) provided with a discharge circuit (21, 21′) controlled by an electrovalve (25) in branched connection between the high pressure supply conduit (7) and the low pressure return conduit (8). The discharge circuit (21, 21′) comprises a discharge valve (22) whereof the opening and the closing are slowed down by a calibrated orifice (23). The discharge valve (22) located upstream of a discharge orifice (27) provided on the return conduit (8) enables to deviate part of the non-injected fuel flow towards the nozzle needle (5) to exert thereon a closing pressure. Consequently, this results in a better control over the opening and closing of the nozzle needle (5).