Symptoms of Bad Spark Plugs
Spark plugs play a critical role in the working of internal combustion engines. The spark plugs are used to ignite air and fuel mixture inside the combustion chamber. Therefore, faulty spark plugs start showing symptoms at an early stage. Not replacing or ignoring the symptoms can cause a number of issues in the smooth functioning of a car.
In this guide, we have enlisted some of the common bad spark plug symptoms that will help in diagnosing the issue more conveniently.
Bad Spark Plug Symptoms
Spark plugs are counted among engine components that require proper maintenance and care. It is sensitive to debris and starts malfunctioning when affected by dirt or debris built-up. Here is the list of symptoms that represent a bad spark plug.
Trouble in Car Ignition
A faulty spark plug can cause ignition switch problems. Worn-out and malfunctioning spark plugs have problems in creating enough spark to ignite the mixture inside the combustion chamber. Due to this, the car dies immediately after starting and requires multiple attempts to start properly. Moreover, it will also cause the engine to idle due to differences in cylinder position and spark.

Lower Fuel Economy
It is the most common side effect of bad spark plugs. A bad spark plug can decrease your fuel economy by 30%. Old spark plugs start passing the deposited debris inside the combustion chamber which creates an impact on fuel-burning efficiency. The presence of these pollutants in the chamber also causes car exhaust to emit black or different color smoke.
Illuminating Engine Light
An engine warning light will illuminate immediately to indicate a faulty spark plug. Modern cars have self-fault detection technology that can identify malfunctioning spark plugs. It will also create a car backfire leading to cuts providing an uncomfortable driving experience.

Engine Knocking and Misfiring
Spark plug failure symptoms also include engine misfiring and knocking. You can witness engine knocking and misfire usually during acceleration. It happens when spark plugs fail to combust air and fuel ratio properly. The unburnt mixture catches fire and detonates when the piston is at the opposite position. Therefore, either you hear engine knocking or misfiring.
Reduced Acceleration
Spark plugs are responsible for combusting fuel and generating energy to run petrol or diesel engines. When spark plugs fail to combust properly less energy is generated which creates a negative impact on acceleration. Generally slow or no acceleration is felt due to a faulty spark plug.
Inspecting a Faulty Spark Plugs
A faulty spark plug can elaborate a lot about the engine and its component’s health. It is often used by professionals to gauge the current engine condition. Here we have mentioned a few spark plug conditions and what they denote about engine health.

- Worn-Out Electrode: It is common that electrodes get worn out. It does not represent any alarming engine condition.
- Black and Dry: A black and dry spark plug represent a leaky fuel injector or fuel control problem.
- Clean Plug: A completely clean and spotless spark plug shows coolant leakage in cylinders. This coolant is steam cleaning the spark plug and making it spotless.
- Evenly Worn-Out Electrodes: Worn-out electrodes with no deposit or debris represents normal engine condition.
- Dry: When the end of the spark plug is dry and sandy it is not a good sign. It presents oil leaking in the engine and reaching to valve sealings and another components.
- Wet Deposits: Greasy-looking spark plugs represent liquid oil penetration in the engine which represents leaking cylinder head or other major malfunctioning.
How to Replace Bad Spark Plugs
Replacing spark plugs at home is not a difficult job, you can easily replace it at home. However, few handy tools are required, if you do not have any of these tools buy auto accessories for sale in the UAE. See the following process of replacing spark plugs.

- Unwire the spark plugs
- Check if there is any water or debris over the plug. If yes, then clean the area properly
- Use magnetic sockets (screw wrench) to unassemble the spark plug from the socket it is fixed in
- Inspect the spark plug if it needs to be replaced, or it is something else
- Place the new spark plug and use a torque wrench to screw the spark plug
- Read the user manual to know the ideal turns require for assembling a spark plug
Cost of Replacing Faulty Spark Plugs
The car spark plug replacement cost is not high. The starting price of spark plug is from AED 40 which can vary from car model to model. However, between iridium and platinum spark plugs, the prices start from AED 180 and AED 125, respectively.
The spark plugs seem to be a smaller engine component that is not difficult to change, but it plays a significant role. Therefore, symptoms of faulty spark plugs should not be ignored for a better driving experience.
These were different signs of faulty spark plugs that you should not ignore. Combustion engines will not work without spark plugs. This smaller engine component is important and requires regular maintenance. Car’s manual presents information about when to replace spark plugs, but it can create a lot of hassle. If you want to avoid this hassle, switch to electric vehicles. Electric cars don’t use spark plugs, browse through these used cars for sale in the UAE. We also have enlisted some of the best electric vehicle models for you.
Stay tuned to UAE’s top auto blog for more information on spark plugs.