One of the most common issues afflicting older BMW E46 3 series cars
is a failing or broken fuel pump. Like all mechanical parts on your BMW, the fuel pump has a limited lifespan...it, unfortunately, doesn't last forever. Age and general wear and tear take their toll on internal parts, causing the pump to lose its ability to create and hold proper fuel pressure. Dirt and debris in the fuel can slowly clog the pump causing it to overheat under the additional workload leading to pump failure. A BMW E46 fuel pump can deteriorate slowly or it can break down without warning...there is unfortunately no standard formula. Common symptoms of a failing pump include engine hard to start, engine stalling, whining or irregular sound coming from under the rear seat, and decreased performance. If the fuel pump completely fails, the vehicle will not start.
The BMW E46's fuel pump
is located underneath the rear seat on the right side of the vehicle. It is an "in-tank" submersible pump that draws fuel through an inlet valve and pressurizes it through a feed line to the engine's fuel injectors. The E46's fuel pump is controlled by the vehicle's DME (engine control unit). When the ignition key is turned to the start position, the DME closes the fuel pump relay allowing power to be sent to the pump. The fuel pump operates continuously while the engine is running providing a steady flow of pressurized fuel to the engine.
The good news is a BMW E46 fuel pump replacement is a relatively simple repair, even for the beginner mechanic. The pump is easily accessed under the rear seat and there are no special tools needed to complete the repair. In fact, a BMW E46 fuel pump replacement can be performed in about 30 minutes with just a socket wrench and flat blade screwdriver.
Since there are other factors that can cause a BMW E46 fuel pump not to operate, we strongly recommend reading our article BMW E46 Fuel Pump Test
. Even though the article deals specifically with E46 325i models, it gives excellent information on diagnosing relay-controlled fuel pumps in any BMW.