What Causes Black Build-Up on the Spark Plugs in a BMW?

BMW Used Spark Plug

Every component in your vehicle, including your spark plugs, is crucial to the vehicle’s smooth running of all its systems. The spark plugs are the reason your BMW starts whenever you turn the ignition. They are inside the combustion chamber, where they ignite the fuel/air mixture and allow the engine to produce horsepower.

One of BMW’s most commonly-seen problems is the buildup of carbon around the spark plug. This carbon buildup can primarily be attributed to the disproportionate mixture of air and fuel, when it contains excess fuel, resulting in incomplete combustion. Below are some of the most common causes of carbon buildup on your BMWs’ spark plugs.

Causes of Carbon Build Up

Although a vehicle spark plug has a life expectancy of 30,000 to 90,000 miles, several factors could accelerate their wear, leading them to fail earlier than expected. Discussed below are possible causes of your spark plug failure:

  • Rich Fuel Mixture: The ratio of the air and fuel present in the combustion chambers should be proportional for smooth combustion. A rich fuel mixture is one containing excess fuel in the mixture. When this happens, there will be incomplete combustion resulting in excess carbon sticking to the hot parts of the spark plug. This can be observed by the buildup of a black substance with a light texture around the spark plug.
  • Long Idling: When the engine idles, it undergoes partial combustion, resulting in fuel residue buildup on cylinder walls. The residue could clog your spark plugs. Thus, you should always avoid idling the engine for long if you intend to stay parked for long to prevent carbon deposits from fouling your spark plugs.
  • Frequent short distance commute: A spark plug only functions effectively when its center electrode temperature is between 500 and 950 degrees Celsius. Whenever the center electrode temperature is below this range, excess carbon generated due to incomplete combustion is deposited on the surface of the insulator. Consistent short-distance trips could lead to carbon deposit buildup on the spark plugs because the engine doesn’t reach the optimal temperature. Consequently, the issue could result in ignition failure.
  • Clogged air filter: Your BMW’s air filter allows clean air into the engine. Hence, the air filter is the engine’s first line of defense against airborne contaminants. Over time, the air filter can become clogged with contaminants, reducing the filter’s efficiency. A dirty air filter restricts airflow into the engine leading to excess fuel in the combustion mixture. The impact of a rich fuel/air mixture is unburned fuel which turns into soot residue that accumulates on the spark plug.
  • Faulty oxygen sensors: The function of the oxygen sensor is to calculate the amount entering the engine and relay the information to the engine’s ECU. The vehicle computer informs the fuel system to deliver adequate fuel for engine combustion. If the oxygen sensor fails, it could communicate erroneous data to the ECU, causing excess fuel delivery to the combustion chamber and incomplete combustion. Consequently, incomplete combustion causes carbon buildup on the spark plugs.

Symptoms of a Faulty Spark Plugs

The spark plugs ignite the fuel/air mixture for engine combustion to occur. If the plugs become fouled with carbon buildup, you may notice Increased fuel combustion, engine misfire, rough idle, delayed acceleration, difficulty starting your vehicle, sudden acceleration, etc.

You should consult our BMW specialists for proper diagnosis whenever you notice one or more of these symptoms. Leaving the problem unattended could result in further complications, which could cause the total breakdown of your engine.

Bring Your BMW to Mike Johns Imports For Quality Repair & Services

Here at Mike Johns Imports, we recognize the BMW Spark Plug Carbon Build Up Check importance of a well-functioning vehicle and know that faulty spark plugs can cause frustration. We provide swift and quality responses to whatever issue your BMW might have. Our team of experienced technicians has decades of experience working on BMW and MINI vehicles. We are equipped with the latest tools and equipment needed to repair or maintain your vehicle.

We are located in Jeffersonville, IN, and also welcome drivers from across Crestwood, Hurstbourne, Jeffersontown, Louisville, and St. Matthews. Do not hesitate to give us a call today or drive into our service center. We guarantee your BMW will be back on the road in top condition!

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