9 Symptoms Of Bad Spark Plugs

Even though it’s small, a spark plug is a very important piece of equipment. Its job is to get the car started. This is done by the spark plug, which makes a spark that lights the air-fuel mixture in the combustion engine.

For your engine to run at its best, the spark plugs should be clean and the electrodes should not be broken. If your spark plugs get dirty or clogged, it can make your engine run less well. A fouled or bad spark plug is one that is covered with something like oil, fuel, or carbon, or is blistered from running too hot. When you drive with dirty or broken spark plugs, you can cause a lot of damage to your engine. Some signs of bad spark plugs are:

Many people don’t know how to tell if a spark plug is bad, though. Some of the most common signs that spark plugs need to be replaced are:

  • Engine Misfires
  • Exhaust Smells like Gas
  • Engine knocking
  • Difficult starting
  • Rough Engine Idling
  • Loud Engine Sound
  • Poor Fuel Economy
  • Check engine light is ON
  •  Slow Acceleration 

Here’s a closer look at how each of the signs can be caused by bad spark plugs.

Engine Misfire

There are many things that can cause an engine to misfire, like bad fuel or valves that leak, but those may not be the only culprits in this case. A misfire in an engine is often caused by at least one old spark plug. When this happens, the owner of the car will notice that the engine speed slows down and then speeds up again.

You may also hear a “pop” from the engine when it loses power before regaining the right timing. When an engine misfires, raw fuel goes into the exhaust, raw fuel goes out the exhaust. In the end, this damages the catalytic converter, which can lead to expensive repairs.

Exhaust Smells Like Gas

If your spark plug doesn’t burn the air-fuel mixture well, unburned fuel (or gasoline) will get into the car’s exhaust system. Because of this, the exhaust from the car may smell like gasoline.

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The smell could be caused by a number of things, but the spark plug is a good place to start.

Engine Knocking

Sometimes, especially when you speed up, your engine will make a clear knocking noise. That sound is because your spark plugs aren’t working right and aren’t letting the fuel burn. The fuel and vapor that didn’t catch fire will eventually do so and go off. When this happens, your engine makes a knocking sound. Engine knock is often caused by bad spark plugs, which are easy to fix.

Difficult starting

If your spark plugs are dirty, broken, or worn out, it can be hard to get the spark needed to start your car’s engine, especially when it’s cold outside. This could make the car start jerkily or make the engine crank for a long time before it starts. If this keeps happening, it can hurt your car’s engine and starter and drain the battery.

Rough Engine Idling

Your engine should sound smooth and steady, and its RPM should stay the same.

But if your spark plug is bad, your car is likely to have a rough idle. In particular, you’ll hear rattling noises, feel a lot of vibrations, and see sudden changes in the RPM of an internal combustion engine.

When your ECU (Electronic Control Unit) attempts to compensate for a failed spark plug and loss of power, the engine may idle roughly.

Loud Engine Sound

Whether you drive a car with four, six, or eight cylinders, if the engine makes a really loud noise, you should know that at least one of the spark plugs isn’t working right. 
When the spark plugs don’t work right, they make the engine’s cylinders less effective, which makes the cylinders rattle. These annoying sounds mean that the cylinders are working too hard, which will cause more problems in the future.

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Poor Fuel Economy

Poorly maintained spark plugs can cost you more than just the cost of replacing a catalytic converter. If the spark plugs aren’t in good condition, they can’t burn the gasoline in the combustion chamber well. When this happens, the engine needs more fuel and needs to use it more often to work right. This is called bad fuel economy. 

Because of this, a car owner will notice that when the spark plugs are worn out, it’s not just the engine that has to work harder. When those spark plugs wear out, You will have to buy more and more gas, which will cost you a lot of money.

Check Engine Light Is ON

Via Edmunds.com

Even if a You are forgetful, the car’s internal system has ways to remind them that they need to make an appointment for car maintenance. When an engine’s spark plug is covered in oil and carbon or has blisters from running too hot, it can cause a lot of problems.
It can be very helpful to pay attention to the check engine light. This light is a warning that you should call a mechanic, even if the engine isn’t making any strange noises yet.

Slow Acceleration

If you step on your gas pedal and the car doesn’t respond as quickly as usual, it could be because of your spark plugs. But this could also be caused by things like dirty fuel injectors, broken oxygen sensors, or a broken fuel pump. So make sure that a qualified mechanic checks out your car before you pay for new spark plugs.


How long do spark plugs usually last?

The engine’s performance can be affected by how well the spark plugs are working. Even though spark plugs are used a lot (they “spark” thousands of times per minute! ), they don’t need to be replaced very often.

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Most car makers recommend getting new spark plugs every 30,000 miles, but depending on the type of spark plugs your car has, you may be able to go up to 100,000 miles. For instance, a spark plug made of copper won’t last as long as one made of a stronger material, such as platinum or iridium.

Always replace spark plugs in pairs (one for each cylinder) and use the plugs specified by the owner’s handbook or the vehicle’s manufacturer.

How much does it cost to change a spark plug?

Changing the spark plugs in your car can cost between $100 and $250 on the low end and between $250 and $500 on the high end.

This price covers:

Cost: A copper spark plug costs between $2 and $10 each, while a premium spark plug made of iridium or platinum costs between $20 and $100 each.
Cost of labor: For a four-cylinder engine, expect to pay $60–$140 for labor, and for a six-cylinder engine, $260–$320.
The total cost can also change based on the make and model of the car, the brand spark plugs used, your location, 

Can I change a bad spark plug myself?

You can.

But only do that if you know a lot about cars and have a lot of experience with them.

If you don’t know how to replace the spark plugs, you could hurt the engine’s performance and have to pay for more expensive repairs in the future.

Also, a professional mechanic can give you better advice based on the state of the spark plugs.

For instance, if your spark plug has oil on it, there may be other problems with the engine and ignition system of your car. If that’s the case, you could put in new spark plugs, but they’d just get dirty again.

How To Change Spark Plug

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