How to Identify Fouled Spark Plugs: Common Signs and Solutions

The spark plug plays the most important role in igniting the air-fuel mixture inside the combustion chamber (cylinders) that powers your vehicle. Spark plugs become fouled after a certain time period Or for some reason. The engine cannot start or run efficiently without proper spark plug functioning.

Here is a guide to the steps, signs of a fouled spark plug, how to fix it, and preventive maintenance to achieve maximum performance.

Understanding Fouled Spark Plug?

When the spark plug is covered with unnecessary substances, such as carbon, oil, or fuel, it will affect performance, fuel economy, and engine starting issues. Excessive overheating can damage spark plugs. Driving with fouled spark plugs can lead to other engine problems.

What are the Signs of a Fouled Spark Plug?

Some signs indicate the spark plug is carbon coated (rusted), causing current leakage. That’s why it does not provide enough spark to ignite the air-fuel mixture in the cylinder.

1. Contaminated Spark Plug

Spark plugs are always exposed to high temperatures. In some cases, oil, fuel, and coolant are contaminated, which causes an extra coating of different substances(corrosion). Anyone can check it visually or compare it to a new piece easily. Normally, no one pays attention to this type of check until some other problem arises.

2. Difficulty Starting the Engine

A spark plug is the main part that starts the engine, and the ignition cycle is completed. If they are very bad, they will not be able to crank the engine over. Initially, it will take seconds, but gradually, it will fail to start the engine.

3. Misfiring Engine

When ignition is not completed in the combustion chamber, the engine will misfire. Initially, you can notice a stumble or sputter.

This may be the cause of sensor failure; you can check the engine light notification that appears on the dashboard. 

4. Poor Fuel Economy

A fouled spark plug does not burn fuel perfectly, so it requires more gas to achieve the required power and affects fuel economy. The spark plug gap also plays an important role in fuel efficiency, so it needs to be adjusted according to factory specifications.

5. Decreased Response When Accelerating

A fouled spark plug and disturbed ignition cycles cause the engine to not respond properly when the gas pedal is pressed. Other causes of late responsiveness may also exist. 

6. Rough Idle

You can notice when the car is parked or stops at a signal that the RPM needle is going higher or fluctuating, and there is abnormal engine sound and vibration. The ECU tries to adjust accordingly, not to shutdown the car engine. A fouled spark plug could be the cause.

7. Strange Exhaust Smell

If the spark plugs do not burn the complete Air-fuel mixture in the combustion chamber, this uncombusted fuel comes along with exhaust fumes at the back of the exhaust out pipe. When you smell gasoline on the back side, it could probably be the cause. However, it’s also because of sensor failure.

Causes of Fouled Spark Pugs

It usually occurs when internal oil leaks through valve seals or piston rings in the combustion chamber or when the spark plug is not replaced as per the service schedule.

The following are detailed causes that will help you to prevent such an issue.

1. Oil Contamination in the Combustion Chamber

When oil remains in the combustion chamber, it causes a fouled plug, which stains the tips over time and leads to failure.

This is mostly noticed in older cars, which consume more oil than normal. 

2. Carbon Buildup

When the tip of the spark plug is black and coated with dry smoke, carbon buildup on the electrode creates a poor spark.

This is because of dirty air filters and fuel injectors leading to contamination.

3. Overheating Engine

When the engine overheats because of a failed cooling system or pre-ignition, the spark plug electrode wears out before time and can damage other parts. 

4. Wrong Plug Gap

The spark plug gap is very important. The spark needs a specific gap to jump. Engine performance, fuel economy, and early erosion of the spark plug are mostly caused by the electrode gap. Every vehicle has a different gap calibration, and a new pre-gapped spark plug needs to be set with a plug gap tool. Follow the user guide manual for best performance.

How to Fix (Clean) Fouled Spark Plugs.

However, cleaning spark plugs is not a permanent solution, but you can try it in some instances. It’s the cheapest way, but it saves time. It will not perform as well as a new one, but it is good if you are not in a position to buy a new one.

To clean the spark plug, follow the steps:

1. You can wipe the firing tip and plug the surface with a clean rag or (zero sand paper) so the electrode is shiny and clean.
2. Use a cleaning spray such as WD-40 and wait to dry for ten minutes.
3. Rub the spark plug tip with a wire brush to clean the remaining deposits.
4. Use pressure air on the spark plug firing tip.
5. Cross-check the spark plug gap with the help of tools; follow the guidebook.

Also, watch the below video for more details.

FAQ‘s

Conclusion

Fouled spark plugs significantly impact your vehicle’s performance and fuel efficiency.

If you understand the causes of spark plug fouling and how to take preventive measures, following all guidelines will ensure that your car engine is running smoothly and avoid costly repairs.