Fuel pump (Mercedes-Benz S-Class W116)

The fuel pump is driven by a pusher from an eccentric on the oil pump drive shaft. The pump parts are shown in Fig. 130. The pump does not require disassembly. The pump operation can be checked without removing the pump from the engine. To do this, perform the following work:

Check the vacuum at the pump inlet:

disconnect the fuel lines from the pump. Install a vacuum gauge at the pump inlet. Disconnect the ground wire from terminal 1 (ignition coil, ignition distributor). Turn on the starter and rotate the engine shaft to the maximum vacuum gauge reading. Turn off the ignition and record the vacuum gauge reading. The nominal vacuum value is 335...470 mbar (250...435 mm Hg) and the drop in vacuum during one minute should not exceed 95 mbar (76 mm Hg).

Check the pressure at the pump outlet:

connect a pressure gauge to the pump outlet. Turn on the starter and rotate the engine shaft to the maximum pressure gauge reading. Turn off the ignition and record the pressure gauge reading. The nominal pressure value at the pump outlet is 0.25...0.38 bar and the pressure drop over one minute should not exceed 0.05 bar.

If the vacuum or pressure at the outlet is less than the nominal values, it is necessary to check the condition of the rubber sealing ring "1" in Fig. 130. If necessary, replace the ring and repeat the check.