This fuel feed pump draws diesel from the tank and delivers it to the injection system at the required pressure and flow rate. It is mounted on the engine block and is driven by the camshaft or an intermediate gear; the pump maintains a steady supply to the high-pressure injection pump, preventing cavitation and ensuring consistent fuel delivery under load. A worn or failing pump causes hard starting, loss of power under load, or erratic engine speed as the injection pump receives insufficient fuel. The manufacturer machines the pump body and internal components to the same tolerances as the original assembly, so the mounting flange aligns with the drive without shimming and the plunger-to-bore clearance matches the original specification for proper volumetric efficiency. When replacing, inspect the drive coupling for wear and replace the gasket between the pump and the engine block.