A bad fuel pump can greatly affect the performance of a BMW. The fuel pump performs the essential function of getting the fuel from the gas tank to the engine's fuel delivery system, making internal combustion in the engine possible. Without the proper amount of fuel, or any fuel at all, a BMW will not run properly.
If the fuel pump is bad in a BMW, the car's engine will not start. The car's electrical system will run normally, but the mechanical parts of the engine will not move at all. If you listen closely, especially with the window or door open, while you turn the car's ignition you will hear a clicking noise but nothing else.
BMW's with a bad fuel pump will constantly stall out. Often after starting up the car will stall quickly and will need to be restarted. The stalling out can even affect how quickly the car can travel, making it so the vehicle will only travel at a slow rate as the engine struggles to run. The stalling out will usually be constant for a period, but it can also cease for a time only to return and become chronic once more.
If the BMW runs fine, but suddenly the engine starts to shake violently, it is usually a sign of not enough fuel reaching the engine. A plugged fuel filter or other parts in the fuel delivery system could cause the lack of fuel, but often the culprit is a faulty fuel pump.