This overflow valve regulates fuel pressure within the engine-mounted fuel system. It opens at a calibrated pressure to return excess fuel to the tank, maintaining a stable supply pressure to the injection components. A valve that fails to seat properly or opens at the wrong pressure can cause hard starting, irregular idle, or reduced power output. This component is manufactured to the original spring-rate and seat geometry specifications, so it maintains the correct cracking pressure without adjustment. On installation, ensure the sealing surfaces are clean and the valve is torqued to the specified value.