Fuel Injector Fault
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A fuel injector fault occurs when one or more injectors fail to deliver the correct amount of fuel to a cylinder. This can happen due to electrical failure, internal clogging, leaking, or coding issues on newer BMW models. The result is a cylinder misfire, rough idle, or loss of power. If the fault is confined to one cylinder, the injector itself is a prime suspect.
What it feels like
You'll typically notice a rough idle or hesitation under light load, especially when the engine is cold. The check engine light will illuminate, often with a specific cylinder misfire code. At highway speeds, you may feel a subtle vibration or hesitation when accelerating. In some cases, fuel smell around the engine bay suggests a leaking injector. Raw fuel odour in the exhaust or black soot on spark plugs are common signs. Fuel economy may also drop noticeably if an injector is stuck open or leaking into the cylinder.
How to confirm it
- Scan the engine for misfire codes and fuel trim data. A misfire on a single cylinder paired with long-term fuel trim adjustments on that bank points toward the injector or fuel delivery.
- Compare the cylinder number in the misfire code to known fuel injector issues or fault codes specific to that cylinder. If a code like P0301 (cylinder 1 misfire) appears, that cylinder's injector is a candidate.
- Swap the fuel injector with another cylinder if your engine layout allows it, then rerun the diagnostic. If the misfire follows the injector, the injector itself is faulty. If it stays on the original cylinder, look elsewhere (coil, plug, compression).
- Check injector connectors and wiring for corrosion or damage. Use a multimeter to test injector resistance (typically 10-15 ohms on most BMW injectors) and listen for a clicking sound when the key is on, indicating electrical actuation.
- After replacement, verify that the new injector is coded or calibrated correctly if your BMW model requires it (common on N54 and N55 engines). Incorrect coding can cause persistent misfire even with a new injector installed.
Parts that fix it
Fuel injector faults often require replacement of the injector itself or, in some cases, the high-pressure fuel pump if supply pressure is low.
Genuine BMW N54 N55 - High Pressure Fuel Pump by Genuine BMW - 1237.57. Fits N54 and N55 equipped models; replacement required if fuel pressure is below spec and multiple injectors are misfiring.
Sources
- https://www.bimmerforums.com/forum/showthread.php?2435109-cylinder-misfire-causes
- https://www.e90post.com/forums/showthread.php?t=639708