Leaking or Stuck Injector
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A leaking or stuck-open fuel injector floods one cylinder with excess fuel, fouling the spark plug and causing misfires. This typically affects only one cylinder and shows up as a sooty or fuel-smelling plug during inspection. On BMW N54 and N55 engines, injector faults are a common cause of single-cylinder fouling. The problem can range from a slow weep to a fully stuck injector valve, and it degrades driveability until diagnosed and replaced.
What it feels like
You may notice a rough idle, especially when the engine is cold. Power loss or hesitation under acceleration is common. The check engine light typically illuminates with a misfire code for one specific cylinder. Some owners report a fuel smell from the exhaust or inside the cabin. On the road, the engine may feel slightly uneven or produce a ticking sound under load. If the leak is slow, symptoms can be subtle. If the injector is fully stuck open, the misfire is much more pronounced.
How to confirm it
- Pull all spark plugs and inspect them visually. A plug fouled by excess fuel will appear dry and matte black, distinct from oil fouling (shiny black) or coolant intrusion (chalky white). Note which cylinder shows fouling.
- Read the engine control module with a BMW scanner and compare misfire counts by cylinder. A single cylinder with high misfire counts points to a localized problem such as an injector.
- Physically inspect the fuel injector connector and wiring for corrosion or looseness. Unplug it briefly and check for fuel seeping from the injector tip while the ignition is on (fuel pump pressurized).
- Swap the suspect injector with a healthy one from another cylinder and drive the car. If the fouling and misfire move to the new cylinder, the original injector is faulty.
- Check the injector code adaptation data in the DME. A stuck or leaking injector often shows skewed adaptation numbers for that channel.
Parts that fix it
Replacement fuel injectors and related fuel system components are available from OEM and aftermarket suppliers. The correct part depends on your engine code and model year.
Genuine BMW N54 N55 - High Pressure Fuel Pump by Genuine BMW - 1237.57. Required for proper fuel system pressure on direct-injection models, works with new or refurbished injector sets.