What Are Fouled Spark Plugs?

Spark plugs are an essential part of automotive ignition systems. They work in conjunction with ignition coils to ignite the mixture of air and gas in the engine's combustion chamber.

When starting your vehicle, the ignition coils will send electricity from the battery to the spark plugs. The spark plugs will then create a spark using this electricity to ignite the air-gas mixture. Spark plugs, however, don't last forever. Most of them have a lifespan of about 80,000 to 100,000 miles.

Spark Plug Fouling Explained

Spark plug fouling is a phenomenon in which spark plugs accumulate a layer of debris -- typically soot-like carbon. While available in different types, all spark plugs share a similar design. They feature a pair of electrodes at the top. Electricity will essentially "jump" from one electrode to the other electrode, thus creating a spark. Over time, carbon, oil and other contaminants will build up on these electrodes.

The Impact of Spark Plug Fouling

If your vehicle has fouled spark plugs, you may notice one or more symptoms. You may struggle to start your vehicle, for instance. As debris builds up on the electrodes, the spark plugs may fail to create a spark. And without a spark, your vehicle won't start.

Fouled spark plugs can harm your vehicle's gas mileage. Your vehicle's engine may burn more gas to compensate for the fouled spark plugs. If you notice that you filling up at the pump more frequently than usual, fouled spark plugs could be to blame.

Another common symptom of fouled spark plugs is engine misfires. A misfire involves a cylinder failing to create combustion. Each cylinder, of course, should create combustion. With fouled spark plugs, some or all of your vehicle's cylinders may fail to create combustion. Rather, they will misfire.

Does your vehicle shake when idling? Fouled spark plugs could be to blame. Rough idling is a common symptom of fouled spark plugs. When stopped at a red light or sparked in your driveway, your vehicle may vibrate. Rough idling such as this is often caused by fouled spark plugs.

Replace Fouled Spark Plugs

Fortunately, spark plugs are easy to replace. Most vehicles have one spark plug per cylinder. If you drive a four-cylinder vehicle, it will probably have four spark plugs. If you drive a six-cylinder vehicle, it will probably have six spark plugs. Using some basic tools, such as a wrench, you can remove the old spark plugs and replace them with new spark plugs.