Home / Engine Related Issues / Spark Plug Fouling

Spark Plug Fouling

One of the most common causes for engine misfiring is the fouling of spark plugs. Fouling is a term used when plugs become dirty for any reason. And when this happens, sparks plugs will lose their ability to fire, which in turns unable to ignite the mixture of air and fuel inside the engine. Aside from causing a misfire, dirty spark plugs can also cause loss of power and the plummeting of fuel economy. Meanwhile, there will also be an increase in tailpipe emissions in the form of hydrocarbons.

The Main Reasons Spark Plugs Becomes Dirty and Misfire

Your engine’s spark plugs are made with the feature of self-cleaning in the design. This feature should be able to ensure the clean condition of plugs up to a certain point. This is because spark plugs have a coat of ceramic shell around the electrode center. When the plugs get hot, this shell can help in burning off any material that might stick on the plugs, such as excess fuels and oil deposits. Without the ceramic, these materials can stick and cause fouling on plugs. Different spark plugs are usually built with different abilities in resisting fouling, and it will be determined by their “heat range”. Your plugs should be able to get hot enough to stave off any sticking deposits, but not to a point where it might combust or detonate. Your manufacturer will use the correct spark plugs with the suitable specification based on your engine.

In normal conditions, driving with full throttle acceleration such as highway driving can contribute to prevent the spark plug fouling, because this mode will generate enough heat to get rid of deposits around plugs. Meanwhile, city driving in roads that are dominated by traffic jams will not be good for the plugs condition, as the low heat will not be enough to keep the plugs clean. And when those deposits aren’t clean for a long time, the risk of misfire can increase. This is due to the risk of short circuiting the electrical energy around the ignition coil. Instead of igniting the air and fuel mixture, there is a possibility that fouling spark plugs gets short circuited to ground and create unwanted spark.

Spark Plug Fouling

What are the Causes of Spark Plug Fouling?

If you have noticed that misfires keep happening in your engine, fouling might be the reason. And if it still keeps happening after cleaning, then you might have an engine problem. Normal and clean spark plugs are usually colored in brown or light tan. But if you can see a blackened area around them, there might be some oil or ash deposits that signal trouble. Fouling of spark plugs can happen for a few reasons, including:

Damaged valve guides and their respective seals can be the cause. If there is a leak on them, it will allow oil to trickle down and fill the combustion chamber. If you can see oily deposits forming around the plugs, this might be the reason for it.

Worn piston rings as well as damaged engine cylinders could also be behind the fouling. The problems in pistons, such as old piston rings, cracked metals, or even scratches and grooves in the cylinder walls will allow the flowing of oil into the combustion chamber. And if spark plugs can’t generate enough heat to get rid of them, the deposits will stack from time to time.

Rich fuel mixture. The mixture with a larger composition of oil will create black deposits around the spark plugs. Check your engine. If you see that only a few of your plugs are affected, then the cause might be a leak in fuel injector. But if all of them have black deposits, the rich fuel mixture may be the result of a high fuel pressure. You can fix this by checking for a defective fuel pressure regulator, or a disturbance in the fuel return line. If the oxygen sensor is broken and shows a reading of lean all the time, the rich fuel mixture can also occur. Using a scan tool to see the fuel trim reading can help you inspect the engine condition. If the reading result shows a number between -8 and -10, then it means you have a rich fuel mixture running inside. For older engines built with a carburetor, a leaky float or incorrect float setting can also raise the problem of rich fuel mixture. Aside from that, the cause can also come from a leak on the inlet needle valve or the usage of jetting that is too large in size.

Leaky head gasket. One of the worst things that can happen to your vehicles is the leaking head gasket. This is because head gaskets can get very expensive to fix. It can also form dirty deposits on the spark plug. The leaks on the head gasket will let coolant get into the combustion chamber. So, if you notice that your spark plug is fouled, then the reason might be some leaks that are happening on the head gaskets. Adding a bottle of cooling system sealer can be used as a cheap solution temporarily.

Quick Fix for Fouled Spark Plugs

When vehicles are rarely driven, then misfiring caused by fouled spark plugs can happen more often. This can also happen if you only drive short distances or if you let your engine idling for long periods of time. To counter this, you might want to take your vehicle out on the highway. The recommended driving mode for this is to accelerate quickly and drive abnormal highway speeds for at least 20 minutes. If no other problem exists, and the spark plugs will be cleaned.

But if that quick fix to solve your problem, then there might be fouling around spark plugs. If you don’t clean the fouling, then misfiring will always occur. You can try to check the condition of spark plugs by removing them and then inspect it. You can also clean them if there are indeed fouling that formed.

You can also get some spark plug cleaner devices from an auto parts shop. These tools usually blast sand that will clean and remove the deposits. But if you choose to use this, make sure that no sand is left on the plugs after the process. The gap of the spark plug electrode should also be checked to see if they are following the specifications.

You will not be able to clean the spark plugs if there is too much fouling on them. You are going to need to install a new set of spark plugs. This will depend on your engine specification to make sure that they are gapped in the right manner. Always check the vehicle’s specification even though most spark plugs are pre-gapped.

If you are driving in the city and you can avoid short trip driving sessions or driving sessions with a lot of idling, then you might want to get spark plugs that can perform harder than the standard ones. The hot temperature will be able to improve the fouling resistance of the plugs.

But if your vehicles are equipped with a modified performance engine, then the type of spark plugs you want to have is the ones that can perform colder. This is due to the fact that performance engines produce more heat. If you combine the heat from the engines in the plugs, then you will have a greater risk of engine-damaging detonation. But the negative of going this way is that the performance engines will have less effective fouling resistance on the spark plugs.

Normal Spark Plug

Normal Spark Plug

You can check the condition of normal spark plugs by their color. The normal ones will have grayish-tan or light brown on the side electrode. If the color looks normal, then you can use the spark plug again.

Carbon Fouled Spark Plugs

Dry soot can also form around the electrodes and insulated tip of the plugs. The main cause of this is usually a dirty air filter, a rich fuel mixture, low-speed driving sessions, or letting the engines idling for a long time. Ask your mechanic what kind of spark plug that you need to use to replace the damaged ones. Choose the higher spark plug numbers so that they will have a higher fouling resistance.

Spark Plug with Oil Deposits

Spark Plug With Oil Deposits

If the electrodes and insulator tip are covered in black and only deposits, then the spark plugs might be fouled by an oil leak. This could mean that oil is leaking into the cylinders. The main cause can come from pistons that are too old or valve guides that are worn or damaged. Consult a mechanic to find the source of the leak. Address the problem before replacing the spark plug.

Wet Spark Plugs

When spark plugs cannot fire, then the condition is called wet spark plugs. The causes can include unburned gasoline that leads to a short circuit on the ignition voltage. The electricity goes to the ground instead of jumping across the gap on the electrode. The other cause might be the flooding of the engine when you want to start the vehicle in a cold engine condition.

The problem above is usually found in older engines that still have a carburetor. Some other causes might include pumping the accelerator too much, a broken choke, or a problematic carburetor with a leaky inlet valve that lets in too much fuel into the vehicle’s engine. With new engines that have a fuel injection mechanism, flooding will not be a problem unless there is a leak on the fuel injectors. Another cause that might be possible is excess of fuel pressure. You also need to check if the injector valve is stuck. The damage to the EVAP system could also let fuel vapors get sucked into the engine and cause flooding.

You can try to dry the wet spark plugs by holding the acceleration battle all the way to the floor. This mechanism will usually push the engine management system into floor clear mode. You also need to keep the engine cranked to do this.

The problems around the ignition mechanism can also cause the existence of wet spark plugs. If the wires are ignition coils are not working properly, then the plugs will not be able to ignite the air and fuel mixture. If you have an engine with an individual coil-over-plug system for the ignition, some arcing around the coil boot will cause a misfire. This is because that arcing will result in short-circuit to the ground. Another possible cause for this is a bad crankshaft position sensor that has difficulty generating the necessary ignition for signal.

If you have no underlying problems, such as a broken ignition coil, damaged plug wire, or other problems around the crank sensor, then you can try some fixes for the wet spark plugs problem. You can either spray some starting fluid into the throttle body or dry out the spark plugs to get rid of the wet problems.

Wet Spark Plugs

Burned Spark Plugs

A burned spark plug is the result of the plugs running too hot. The signs of these conditions can be noticed by some blistering on the insulator tip, electrodes that are melting, or some white and bright deposits around the plugs. The causes can include incorrect spark plug heat range, overheating the engine too much, or incorrect ignition timing combined with a wrong mixture of air and fuel. This can only be solved by replacing spark plugs.

Spark Plug with Worn Electrodes

When your spark plugs have passed their usage time, then it might be time to replace them. The prolonged usage of the plugs can cause wear and erosions around the plugs.

Spark Plugs with Broken Electrodes

Installing the wrong spark plugs when your vehicles can cause the plugs to break off or even get flattened. The wrong usage of plugs can also contribute to extensive damages to your vehicle engines. Meanwhile, if the size of the plugs is too small or too short, then you can also experience poor gas mileage and some fouling on the spark plugs. Always consult your manual to see which type of spark plug that you should install in your vehicle.

Some problems that can happen if you drive with spark plugs that are dirty or fouled:
Poor gas mileage
If you experience a sudden drop in the vehicle’s fuel economy, then the problem might be caused by spark plugs that are dirty or fouled. Fouling on the spark plugs will cause the plugs to not be able to function properly, which leads to a negative impact on the gas usage.

Lack of acceleration
Prolonged use of idling mechanism could be the culprit of the dirty spark plug. When they get dirty, misfires can happen, and your vehicles will not perform properly.

Ignition problem
If you have trouble starting your vehicle, then your plugs could be the cause. You might think that the battery or empty gas tank might be the main culprit. But the combustion process will not start without a properly working spark plug.

Engine misfires
A faulty spark plug will cause your engine to not fire up and start the combustion process. And when the engine is running, the dirty plugs will also have trouble running an uninterrupted combustion process to support the performance of your vehicle’s engine.

Check Also

Procedure for Diagnosing and Testing an Ignition Coil Featured

Procedure for Diagnosing and Testing an Ignition Coil

Ignition coils are basically the batteries for your spark plugs. They send the power the …