This mechanical fuel pump delivers diesel from the tank to the injection system at the correct pressure and volume. It is mounted on the engine block and driven by the camshaft or an intermediate gear; its internal diaphragm or plunger creates the suction and discharge strokes that keep the injection pump supplied. A worn pump causes hard starting, low power, or erratic engine speed because the injection pump cannot maintain its required inlet pressure. The manufacturer machines the mounting flange and lever geometry to match the original engine interface, so no adapter or modification is needed during replacement.