Top 8 Symptoms of Bad Spark Plug


Every vehicle which uses petrol or gas as its fuel for working requires a spark plug that can produce a spark for the burning of the fuel. Without a spark plug the combustion of the air-fuel mixture in the engine cylinder is not possible. The proper function of the spark plug keeps your vehicle free from trouble. But If the spark plug fails to work properly,  in that case how we can identify whether it is working efficiently or not? In this post, we will discuss the top 8 symptoms of bad spark plug and how they are caused.

Symptoms of bad spark plug

Symptoms of Bad Spark Plug

  1. Trouble Starting
  2. High Fuel Consumption or Low Fuel Economy
  3. Lack of Acceleration
  4. Misfiring of Engine
  5. Rough Idling of Engine
  6. Engine Surging
  7. Engine check light
  8. Black Exhaust Smoke

1. Trouble Starting

When turning ON your car and it doesn’t start then there may be a possibility of a dead battery or the fuel tank being empty. But If the Battery is fine and your fuel tank is at optimum level then this problem may arise due to a bad spark plug. In that situation, you have to check the spark plugs of your vehicle.

2. High Fuel Consumption or Low Fuel Economy:

If you are observing a change in the mileage of your car then this will be due to a faulty spark plug. If the spark plug is not working properly then the air-fuel mixture in the engine does not burn properly and more fuel is consumed, as a result, you will get a low fuel economy.

3. Lack of Acceleration:

During driving your car, If you are pressing your accelerator pedal and your car is not accelerating properly and you feel a lack of power. This problem is caused to a bad spark plug. This is the indication that you have to inspect your spark plugs and change the one that is not working properly. Changing the faulty spark plug will definitely solve your problem.

4. Misfiring of Engine:

When your engine starts misfiring then this arises due to a problem with the spark plugs. Misfiring happens when the spark plugs do not produce the spark at the correct time. When the spark is not produced at the correct time then the proper burning of the fuel is not taking place and you feel a jerky ride and higher emission.

5. Rough Idling of Engine:

When you start your engine, put it on idle running.  And If you observe that your engine is producing a rough sound and there is a lot of vibration then this will be due to the wear in the spark plugs. Now this the time to monitor your spark plugs, identify the faulty one and replace it, and eliminates the problem.

6. Engine Surging:

When your engine makes continuous stop-start motions during your ride then this is the symptoms of bad spark plugs. In this situation, the engine is not working efficiently and it sucks more air into the combustion chamber than normal which results in the engine surging.

7. Black Exhaust Smoke:

Due to a failed spark plug, the combustion of the air-fuel mixture does not take place properly and a lot of black smoke is produced during your ride. You will also observe some oil at your exhaust end. Now, this is the time to change your spark plugs that are not working properly. 

8. Engine Check Light:

If you see an engine check light warning then this may be due to many problems. But one problem may be due to the symptoms of bad spark plugs. If your spark plugs do not work properly then you may also see an engine check light. Now you have to call or visit your mechanic to diagnose the exact problem.

Also Read:

What Causes Spark Plugs To Go Bad

causes of bad sark plug

1. Normal Wear and Tear:

With the passage of time, the spark plugs wear out and do not function properly. Wear and tear in the spark plugs is generally more common when you drive your vehicle at lower speeds.

2. Overheating:

The spark plug of your car gets fail if they get overheated. The overheating problem occurs due to a number of factors, some of the most common factors are

  • Running your engine at a higher speed for a long period of time.
  • Installation of the wrong type of spark plug.
  • The ignition components are not working properly

3. Improper installation:

If the spark plugs are not fitted correctly, they may get damaged and stops working early. So the correct installation of the spark plug is necessary for its efficient working.

4. Fuel Issues:

If the bad quality of fuel and proper ratio of the air-fuel mixture is not used, the spark plugs get fouled or damaged and stop functioning properly.

5. Excessive Idling:

When you run your vehicle in idling for a long time, this may fail your spark plugs.

6. Dirty Air Filters:

If the air filter of your vehicle is dirty and not clean, this will not allow proper air to enter into the engine cylinder and we do not get a proper air-fuel mixture. Due to improper air-fuel mixture, the proper burning of fuel does not occur and this results in the formation of soot on your spark plugs. The soot deposited on the spark plug prevents the production of spark.


We have discussed here the top 8 symptoms of bad spark plugs. If you encounter these symptoms then it is a sign of failure of the spark plug of your vehicle. Now you have to book an appointment with your trusted mechanic to check it and replace the faulty spark plug as soon as possible.

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