Fuel tanks in BMW E30 and E36 models are located under the car, either behind the trunk or below the back seat area, where the tank on these models is partitioned into two parts to accommodate the driveshaft. Fuel movement between these sections is facilitated by a jet action pump and
Fuel Pressure Regulator driven back by the fuel returns it through a venturi effect which obviates need for a mechanical pump. The procedures for removing and installing fuel tanks are model-specific as shown in this example: For E30 models, these steps include draining of all fuel from it; removing rear seat bottom cushion and related components; disconnecting hoses and electrical connections; releasing entire fuel tank etc. Finally, reassemble all parts. While for E36 (except Z3), they entail draining all fuel; taking off rear seat bottom cushion; disconnecting hoses & electric connections; blocking off fuelling lines; detaching heat shield & parking brake cables followed by taking out filler hose then lowering tank with installation being done in reverse order. In relation to Z3, removal process usually includes emptying it of any remaining gas; doing away with rear axle assembly from vehicle's underside; breaking earth straps including ventilation lines attached thereto besides other measures as might be necessary while lowering down as well as raising up tank so that finally it can come off after dropping completely down . Once installed, hoses must be reconnected correctly avoiding kinking or sharp bends in addition to ensuring proper routing of electrical items among them. Trying to start your car without filling up gasoline could lead to bad effects on its pump.