Troubleshooting a Fuel Pump on a BMW 330i


The fuel system on the BMW 330i is controlled by an electronic fuel injector, which means fuel is delivered to the combustion chambers of the engine with a fine mist and not by vacuuming the fuel to the engine, like it does in a carbureted car. The fuel pump on the BMW 330i can be especially vulnerable to mechanical failure when the electronic system in the car is not working properly.

Things You'll Need

  • Voltage meter Someone to assist with the project
  • Listen for sounds. A fully functional fuel pump can be identified by a steady humming sound that comes from the rear of the car near the fuel tank. If you hear crackling, trickling or growling noises, this could be a sign of a faulty fuel pump. The fuel tank in the BMW 330i is located on the right rear (rear passenger) side of the car.

  • Monitor your "check engine" light. If the "check engine" light intermittently turns on and off, there may be a problem with the fuel pump and the fuel injection system. The "check engine" light in the BMW 330i is located on the driver's dashboard above the odometer.

  • Do a voltage meter reading of the pump. Locate the dark green and black wire connecting the fuel pump to the system; in the BMW 330i, you can locate this by lifting the carpet on the underside of the driver's side, right behind the door. Connect a voltage meter to the larger of the four wires, and have someone turn on the ignition. Wait for a flash of voltage, then have someone crank the engine. If you get a reading of 10 to 11 volts, the fuel pump is working.

  • Listen for stuttering. One of the most obvious signs of a failing fuel pump is a stuttering engine that dies out shortly after starting. If you have trouble cranking the engine and the engine stutters and dies out, there may be a problem with the fuel pump. The BMW 330i typically does not make a lot of noise when cranking, so listen for a consistent, light humming sound after the engine cranks to ensure the fuel pump is working properly.

  • Check your Electronic Control Unit (ECU). The BMW 330i is a fuel-injected car, which means it is programmed with an Electronic Control Unit. If this unit is faulty, it will send out the wrong signals and may shut the fuel pump off automatically. The dealership or technician will need to reprogram the ECU for optimal performance. If the fuel pump is still not working after this adjustment, there may be a problem with another part of the fuel injection system.

Tips & Warnings

  • Fuel pump failure doesn't typically set any engine codes. You will need to troubleshoot the problem without conducting a computer diagnostic check.
  • Replacing the fuel pump for the BMW 330i can be expensive. Electronic fuel injection systems are typically much more expensive than the standard carbureted engine Don't modify the fuel pump or any other parts of the car yourself if the car is still under warranty. Any modifications that result in more problems may not be covered under your warranty.

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