How To Clean a Fouled Spark Plug? [Causes, Symptoms, and Fixes]

When a spark plug gets fouled, it will cease to fire and burn the air-fuel combination. As a result, a misfire is produced, causing a loss of power and fuel efficiency and an increase in tailpipe hydrocarbon (HC) emissions.

As a driver, one of the issues you are likely to experience is fouled spark plugs. So, how do you clean a fouled spark plug?

To address this issue, abrasives such as a file or sandpaper may be used to efficiently clean your spark plugs. However, if you don’t have either one, a blow torch could also do a fantastic job.

Keep reading to get all the information you need on how to clean a spark plug.

What is a Spark Plug Fouling?

When your spark plugs get dirty or contaminated, the performance of your engine suffers. A fouled or faulty spark plug has gotten coated with a material such as oil, petrol, or carbon.

It can be caused by blisters due to overheating. Driving with clogged or damaged spark plugs can create a slew of issues with your engine.

Why Does Spark Plug Foul Get Dirty?

These plugs are intended to clean themselves to a certain extent. So when the engine is running, the ceramic coating that covers the electrode heats up and burns off every oil or fuel ash accumulation. Otherwise, it will clog the spark plug.

Yet, the spark plugs must not be overheated to the point of detonation or pre-ignition. So, you can only use the spark plugs that are recommended for your engine.

In fact, full-speed and lengthy rides are good for spark plugs since they produce heat, which helps keep the spark plugs clean.

However, short excursions, city travel, and idling for an extended period are not healthy for the spark plugs as they can’t reach the required temperature to burn off all of the deposits.

What Causes Spark Plugs to Foul Quick?

Spark plugs foul fast because other faults within your engine lead them to wear out prematurely. Check that your valves are correctly sealed and that your ignition system is operational.

If you have oil-fouled spark plugs, inspect the PCV valve. A faulty PCV valve may allow harmful fumes to travel through the piston rings and deposit oil on your spark plugs.

You should also ensure that your automobile is not running too strongly and that the fuel-air combination inside the combustion chamber is enough. This will ensure that your spark plugs have a long life and that you wouldn’t have to replace them.

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Spark Plug Foul Visual Symptoms

If your spark plugs are clogged or damaged, they can cause various issues such as decreased gas mileage, intense vibrations, engine misfires, and difficulty starting the engine. So, if you’re having engine trouble, inspecting your spark plugs is a smart place to start.

Reduced Engine Power

There is no doubt that if your spark plugs are faulty or dirty, your gas mileage will drop. So if you find any of these problems, you should evaluate them.

When your automobile is running, the O2 sensor in front of the exhaust measures the exhaust gasses.

Also, if your gasoline somehow doesn’t burn quite well, the O2 sensor will verify the measurements and determine that your exhaust fumes are not acceptable.

As a result, the engine will be told to pour additional gasoline into the combustion chamber. More gasoline equals more unburned fuel and more trips to the gas station.

Strong Vibrations

The constant wear and tear from engine vibration can cause the electrical connection at the spark plug to loosen.

This raises the voltage necessary to ignite the spark plug, potentially damaging the ignition coil and the spark plug wires.

Additionally, Worn or filthy spark plugs can cause a petrol automobile’s engine to misfire in one or more cylinders, causing vibrations while the car is idle or driving.

Hard Engine Start

One other sign of clogged spark plugs is trouble starting the automobile. When there is no spark within the combustion chamber, the gasoline will not burn, and the engine will not start.

This can be caused by clogged spark plugs, poor compression, faulty connections, faulty coils, a faulty starting motor, or a dead battery.

In fact, when you have problems starting your automobile, the problem can be caused by various factors.

So, if the spark plugs are black from carbon or coated with oil, there is an insufficient spark. However, if the spark plugs aren’t in good condition, you should replace them.

Engine Misfire

Engine misfires are among the most prevalent issues that automobile owners, like you, confront when their spark plugs are faulty or clogged.

This is due to two conditions that might cause the cylinders to function unevenly and cause the engine to misfire; lack of spark or a spark that is insufficiently powerful or delayed.

When this happens, you’ll see that the engine’s operation is radically different and does not function smoothly.

These misfires are loud out from the exhaust and noticeable when you push the throttle. So, there should be some loud bangs when a cylinder is misfiring.

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How to Identify a Foul Spark Plug?

When looking for a faulty spark plug, start with the firing tip. It might be a fouled spark plug coated with a foreign material such as petrol, oil, or carbon.

Instead of bridging the gap and starting the engine normally, this coating will simplify the voltage to follow down the insulator nose, seeping back down into the metal shell and producing no spark.

Several things must be addressed. One of them is if the air-fuel ratio is overly high, which can be caused by faulty carburetor adjustment or a badly performing injection system. Aside from that, a filthy or clogged air filter can also contribute to this rich state.

Another thing to consider is when piston rings or valve seals wear, this will allow oil to flow into the combustion chamber and cause oil fouling.

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How to Clean a Foul Spark Plug?

Spark plug fouling can be caused by a variety of circumstances. As a result, cleaning them differs depending on what caused the spark plugs to foul.

Carbon Foul

If you notice a lot of carbon build-up on your spark plug, it signifies your engine is frequently misfiring or is running too richly.

As a result, the spark plug cannot ignite all of the gasoline spilled into the cylinder. Hence, the carbon on the spark plug accumulates.

It is advisable to replace the fouled spark plug to resolve this issue. Also, ensure that all of the other ignition components are operational.

Check the carburetor if you have a carbureted automobile and the fuel injectors if you have a fuel injection car.

However, if you have a direct injection vehicle, such as an Audi, BMW, Hyundai, Kia, Mazda, Mercedes-Benz, Nissan, Lexus, Saab, Subaru, or Volkswagen, this is typical. Carbon accumulation happens as a result of their engineering and construction methods.

Coolant Foul

In another situation, a blown head gasket indicates that your vehicle is burning coolant. Vapors may be produced by the coolant in the combustion chamber. Hence, these fumes can enter the spark plug, cause rust to form on the threads, and harm the electrode.

To resolve this issue, you will need to change the head gasket, and even the spark plugs with new ones.

This will ensure that your problem has been resolved and that you have no more problems with the ignition system or the spark plugs.

Oil Foul

If you see that the spark plugs have a lot of oil over them, it indicates that the valves are leaking. This will cause the valve seals to fail to seal correctly, allowing oil to leak into the cylinder and ignite. When oil burns, it produces carbon in the combustion chamber and fouls the spark plugs.

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Another cause of oil on your spark plugs is a faulty PCV valve. When this valve becomes blocked, it prevents crankcase pressure from building up. This ultimately allows the oil vapors to pass through the piston rings and leave an oily mess on your spark plug.

Hence, the simplest solution is to replace the spark plugs and leave them for good. Sadly, this is not a long-term fix since your spark plugs may foul and become defective again.

So, the problem can be solved by removing the head and inspecting the valves. Examine their situation and then take action to permanently resolve this issue. Don’t forget to check the PCV valve as well.

Ash Deposits

The accumulation of ash in spark plugs is a very regular phenomenon. These ash deposits might accumulate over time and lead your spark plug to malfunction.

Generally, these ash particles can be formed by the combustion chamber burning oil or fuel additives.

If these deposits cause a significant accumulation. They can obstruct the spark and hinder the spark plug from functioning correctly. This can lead to the development of misfires.

Remove the spark plug and use sandpaper to scrape out the ash deposits to resolve this issue. Check for any additional impurities, and your spark plug should be operational in no time.


Blistering of spark plugs is possible. So If your spark plug is blistered, you’ll see some bubbles on it. Other than that, it will also have a slightly brownish tint.

A poor fuel-to-air combination causes spark plug scorching. More specifically, a low fuel-to-air combination. Blisters seen on your spark plugs are one of the consequences of running your automobile too low.

So, you must ensure that your fuel-to-air mixture is right and that your engine is operational. If you have a carbureted automobile, you may achieve this by adjusting the carburetor. However, if you have a fuel injection system, a simple computer tweak will do the work.

Fuel Foul

If your spark plug is saturated with fuel, it signifies your engine is running too heavily. Hence, the air-fuel combination must be altered, and you must immediately address this issue before it worsens.

So, if you are experiencing this issue, it is a smart option to inspect the carburetor if you are driving a carbureted vehicle.

Perhaps the carb spills an excessive amount of fuel into the combustion chamber. As a result, there is petrol on the spark plug.

The ignition wires should also be checked. If they aren’t good, it implies they’re not doing their job correctly, which leads to a cylinder malfunction.

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If you own a fuel-injected car, check the condition of the coils to ensure they are in correct working order. Misfires and gasoline on spark plug issues might occur if the coil is faulty.

Some other consideration is the injectors. Each time, the injectors must deposit the correct fuel volume into the cylinder. When they’re not doing it, this indicates that something must be broken with your fuel injectors.

They may be inspected using an OBD2 scanner tool connected to your OBD2 port. However, keep in mind that this troubleshooting may necessitate using a more sophisticated scanner to analyze the output of each injector.

As more modern scanners are more expensive, you’ll need to have a budget for them. If you don’t have the money, you may take your car to a shop, and they will diagnose the injector problem.

Gapped Foul

Gap bridges in spark plugs happen when the sediments that link the electrodes become too wide, prohibiting a spark from occurring within the engine cylinder. This might be caused by an accumulation of oil or ash.

The answer to this problem is straightforward. You only have to change the spark plug. However, if you don’t want to replace the spark plug, simply pull it out and wipe it all with sandpaper. This will ensure that the carbon deposits on the spark plug have been removed.

Tips to Avoid a Fouled Spark Plug

Aside from treating the root cause of your spark plug fouling, there is another technique to avoid spark plug fouling.

Following the primary purpose of a spark plug, the firing end temperature of the spark plug must be kept low enough to avoid pre-ignition yet high enough to prevent fouling. This is called “thermal performance,” and it is governed by the chosen heat range.

Frequently Asked Questions (FAQs):

Aside from the information provided above, you might have other issues regarding the fouling of your spark plug. So, here are the most frequently asked questions and the answers to them.

Will fouled spark plugs clean themselves?

The answer is yes. Spark plugs are designed to self-clean. So, stepping on the gas and driving your automobile for a fast 20-minute drive on the highway would do the thing in cleaning your clogged spark plugs.

Can you still use fouled spark plugs?

Yes, you can. Your fouled plugs can be cleaned and reused. Every fifty hours, clean, gap, and test spark plugs. If you obtain a clogged plug, use carb cleaning or sandpaper to remove the deposits. Use a brass wire brush to remove difficult deposits (the brass will not harm the electrode).

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What is the quick fix for fouled spark plugs?

If you have only driven your car on occasion, or for short distances, or the engine has remained idle for 15 minutes or longer. It can cause your spark plugs to become clogged and your automobile to misfire.

So, you must take it onto the road, accelerate aggressively, and run it for 15 to 20 minutes at the highest speed limit permissible in your location. When the fouling is not caused by unusual means, it will automatically clean the plugs.

If it still misfires due to fouling, the plugs may be unclean or worn. You may also remove the spark plugs and check them, clean them if feasible, or replace them.

How do you get debris out of your spark plug?

There are various ways to clean the spark plug. You can either use the items below alone or one after the other for the greatest results.

  • File
  • Blowtorch
  • brush made of wire (wire brush)
  • 220 grit sandpaper
  • Airgun (for remaining debris)

What happens when you leave a fouled spark plug?

When you leave a filthy spark plugin, it stops working properly. If your spark plugs are fouled, the engine will run rough, lack power, consume more gasoline, or perhaps fail to start at all.

Takeaway: Cleaning Fouled Spark Plugs

After 20,000 to 30,000 miles, spark plug fouling might develop. Whether you want to clean or replace an old plug, it must be done correctly since spark plug fouling can create serious automotive problems.

Any material that accumulates in the spark plug hole or combustion chamber due to cleaning might harm the engine and lead to more significant issues, such as accidents.

In brief, to clean a spark plug safely, use a wire brush or spray-on plug cleaner made exclusively for this ignition component. A strong knife can also be used to scrape away stubborn deposits. However, it is important to remember that you should never use a shot blaster or abrasives to clean a spark plug.

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