Past experiences showed that the retainer life varied across different types of pressure regulators - even when the retainer designs and materials remained the same. The objective of this work was to identify the root causes behind this phenomenon and to improve the retainer life. Both analytical and experimental approaches were employed. For the analytic approach, a CAE tool (the SABER code) was used to simulate the system dynamics of the pressure regulator components (as main spring, valve body, valve ball, retainer, and valve spring) under repetitive pressure surges caused by fuel injection. The predicted relative motions were used to characterize impacts between the valve ball and the retainer, and then to estimate the retainer life through a simplified fatigue model. Effects of nine parameters on pressure regulator's dynamic performance were studied. On the experimental approach, an undercut valve was designed to reduce the retainer stiffness and to ease the impact between the valve ball and the retainer. Not only does this new design improve the retainer life for more than 50%, but also it reduces the fuel pressure variations in the standard tests.