<div class="htmlview paragraph">Fuel rails with integrated damping effect (FRID's), developed for MPI returnless fuel supply system s, effectively reduce fuel pressure pulsations without pulsation dampers (P/D's). One of the remained issues on FRID's is discussed in this paper. Pressure pulsation peak(s) at certain engine speed(s) (P/P engine speed) is significant issue in some cases. Intensive study revealed that the resonance speed is determined by the pressure change period (P /C period) at oil-hammer, induced by an injector open or close. The P/C period control parameters such as the sound speed in a fuel rail were identified, and suggested configurations to shift a P/P engine speed out of the typically used range in engines were established.</div>