Causes And Solutions For Spark Plug Fouling

31 October 2019
 Categories: , Blog


Dirty spark plugs can't function as well as they do when they are clean. Below are some of the reasons for spark plug fouling, and how you can solve the problem.


Spark plug fouling has several causes; below are some of the most common.

Failed Starting Attempts

Failed starting attempts are bad because the engine draws fuel every time you try to start the car. After several failed starting attempts, the fuel may be too much for the spark plug to handle.

Fuel Injector Leaks

The fuel injector is meant to deliver an exact amount of fuel into the combustion chamber and do it at precise moments. However, if the fuel injector is worn-out or damaged and leaking, it may deliver too much fuel and foul the spark plugs.

Short Stop-and-Go Driving

Spark plugs don't foul up at the first hint of fuel. The heat produced by the fuel injector heats up the plug and dries traces of fuel, keeping the plugs clean. However, if you are driving for short distances and stopping, such as you would do in slow traffic, the plugs might not produce enough heat to dry them. As a result, the plugs would foul up and malfunction.

Worn Valve Seals or Gaskets

Various parts of the engine are protected with seals and gaskets to prevent fluids, such as oil, from flowing into the wrong areas. Worn-out valve seals can allow the oil to flow into unwanted areas, such as the spark plugs. The same thing can happen if the head gasket, which sits between the engine block and cylinder head, is worn or damaged.

Worn Piston Rings

Worn or damaged piston rings can also lead to spark plug fouling. This happens when the worn parts allow some fuel or oil to leak into the engine and contaminate the spark plugs.

Rich Fuel Mixture

Lastly, your spark plugs can also foul if the fuel mixture is too rich (has more fuel than it should). In this case, some of the fuel won't burn up completely, and the resultant carbon deposits can foul the spark plugs.


Driving with fouled spark plugs can lead to loss of engine power, engine misfire, poor fuel economy, and increased emissions of dangerous gasses. Luckily, the following interventions can help.

Clean the Plugs

In many cases, cleaning the spark plugs will help get rid of the fouling. There are even dedicated contraptions marketed specifically for cleaning spark plugs.

Replace the Plugs

You can't and shouldn't try to keep cleaning your spark plugs forever. There comes a time when you have to replace your spark plugs, and this is indicated in your car owner's manual. It's also good practice to replace spark plugs if they become too dirty.

Solve the Underlying Issue

Whether you replace or clean the spark plugs, it's also good to diagnose the underlying cause of the fouling and deal with it. For example, if the problem is a rich fuel mixture, you should diagnose it and fix it. Otherwise, your spark plugs will just foul up again soon after.

For more information, contact local automotive repair services.