When the fuel pump has to be changed, it is better to replace the fuel filter also. Observe all precautions and rules when working with gasoline as well as its vapors before starting work on the fuel system. First thing to do is relieve the fuel pressure. In E30 models other than M3 (with an external pump). The access of a fuel pump in the tank involves removal of rear seat cushion can be done by removing rear seat cushion section which is not applicable for a M3 model with an external pump. However, all E30 models including S14 equipped M3s have two pumps, with a main one mounted externally and then there's also a pre-pump or transfer unit inside the gas tank itself. To start off, begin by disconnecting negative battery cable and lower down your tank if full of gasoline before taking out in-tank pre-pump on M3 S14 models and other E30 models." Take away this insulation sheet by sliding it back and up towards the right side cover after lifting up rear seat cushion thereby opening a passage-way to the right side cover "To remove screws from cover, lift it off "Disconnect electrical plug and fuel lines"' In case some gas gets spilled onto ground or any floor surface then caution must prevail." Remove screws from sender part of pickup assembly slowly removing sender so that gas drains into tank" Turn pickup assembly anticlockwise while slowly pulling it out so that fuel could flow back into tank." In order to lock this gasket into place after lowering delivery pipe assembly into gasoline container, perform rotation around clockwise direction which will secure this element within correct position" Replace gasket and insert level sensor unit in assembly using appropriate screws". Reconnect hoses and connector for power supply of diesel engine," Put back insulation sheet then wrap sheath around socket," Then push back facing panel and screw socket using nuts. Finally lift up negative battery terminal wire check for normal operation/no loss of petrol and make repairs as needed.