This supply pump is a fuel-transfer component that draws diesel from the tank and delivers it to the injection system at the required pressure. It is mounted on the engine block and is driven by the camshaft or an intermediate gear; its internal pumping mechanism maintains a steady flow to the high-pressure pump regardless of engine speed. A worn or failing pump causes hard starting, low power, and erratic idle as fuel delivery drops below demand. The manufacturer machines the pump housing and rotor to the same tolerances as the original assembly, so the mounting flange aligns with the drive coupling without shimming. On installation, replace the gasket between the pump and the engine block and torque the mounting bolts to the specified value.