What Causes Spark Plugs to Get Wet & Foul Out?

by Scott Cornell
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Eduardo Fuentes Guevara/iStock/Getty Images

When a vehicle engine is reluctant to start, it often means that the spark plugs need changing. Like many automotive components, spark plugs don't last forever. A common malfunction is a wet spark plug. According to AA1Car.com, this occurs when the spark plug fails to fire, or fouls out. This can be caused by a number of variables, such as engine flooding, or excessive moisture build up.

Engine Flooding

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Failed vehicle starting attempts eventually lead to wet spark plugs, according to E3 Spark Plugs. This happens when drivers attempt to start their vehicles multiple times without success. This can lead to engine flooding, which in turn can soak the plugs so they're unable to form any kind of spark to start the engine. This often happens in cold weather conditions, when spark plugs that are previously worn or fouled require a higher voltage to ignite the engine. In this case, the best thing a driver can do is either wait for the plugs to dry, or remove the plugs and clean them off.

Injector Leaks

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Wet fouling is less common on modern fuel-injected engines, but can happen due to a number of mechanical failures, states AA1Car.com. One example is a leaking cold start injector. This would lead to the creation of a rich start up mixture in the engine compartment that would cause the plugs to foul.

Worn Piston Rings

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In older vehicle engines, worn piston rings or excessive cylinder wear often lead to wet fouling, states Mopar Magazine. This could result in the release of excess oil or gasoline into the engine compartment, which could prevent a spark from forming during an ignition attempt. Wet-fouled spark plugs can be cleaned and re-installed to work effectively.

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