The development of diesel fuel injection systems is a costly and time consuming process often employing “cut-and-try” hardware approaches to achieve desired levels of system performance. To expedite this process, a comprehensive hydro-mechanical simulation has been constructed which offers the capability for evaluating effects of design parameters on the transient response of fuel-injection systems. The design parameters treated include those related to the cam and pump (in-line or distributor type), outlet valve (snubber, delivery or combination), transfer line and injector (DI or ID1). The simulation incorporates a method-of-characteristics technique for determining the spatial and temporal variation in transfer line pressure; other components of the system are represented by ordinary differential equations.The simulation includes provision for the user to alter baseline values of fuel density, viscosity and bulk modulus (variable with pressure) to permit assessment of the effects of fuel temperature and/or composition. The simulation also permits the assessment of the effects of wall distension and fuel leakage. Finally, the simulation contains provision for addressing parallel fuel transfer subsystems such as those which may be incorporated in solenoid valve-controlled fuel injection systems.A description of the simulation is provided together with a discussion of the physical and mathematical models used. Sample applications of the simulation addressing design considerations along with comparisons between simulation results and experimental data are presented.