Updated at: 01-07-2022 - By: Lucas

Spark plugs are important parts of the internal combustion system of a gas engine. They are in charge of turning the electrical signal they get from the ignition coil into a spark that will light the mixture of air and fuel in the combustion chamber.

Extreme temperatures, dirt, and normal wear and tear all cause these parts to break down over time. When this happens, you’ll notice that your engine isn’t running right, so you should change the oil when the manufacturer says to.

Spark plugs wear out over time, and if they aren’t replaced, they can cause the engine to run less well, break down, fail to start, or cause pollution problems. Spark plugs usually last between 30,000 and 80,000 miles, but this depends on the brand.

If you don’t stick to this schedule, you can expect to run into the following 8 problems!

Issue #1 – Reduced Gas Mileage

Reduced Gas Mileage

Most of the time, when spark plugs aren’t working right, the car uses more gas. When spark plugs get old, the space between the electrodes gets bigger. This makes it more likely that the engine will misfire.

In the same way, soot could build up between these contacts and make it less likely that a spark will happen.

If this happens, the mixture of air and fuel will be pumped into the combustion chamber, but it won’t catch fire. Because of this, the car will use more gas but have less power. To get enough torque, you have to step on the gas pedal more.

If your spark plugs aren’t working right, you could use up to 30% more gas. This means you’ll spend more at the gas station.

Issue #2 – Engine Backfire

A backfire happens when the mixture of air and fuel burns or explodes outside of the combustion chambers. In some cases, the backfire goes up the intake valve, which causes parts of the engine to break.

Most of the time, though, it goes out through the exhaust. When you rev the engine, a flame will come out of the tailpipe of your car.

One reason for this problem is that the spark plugs are worn out. Since they won’t make the spark at the right time or at all, the mixture of fuel and air won’t catch fire. Instead, when the exhaust valves open, it will leave the cylinders while it is still flammable.

If the mixture burns through the exhaust system, the flame back there might look cool, but it will hurt the catalytic converter. It’s no joke to replace this part!

A catalytic converter can cost over $1,000, so it’s better to change the spark plugs when they need to be changed.

Issue #3 – Harmful Emissions

Harmful Emissions

Internal combustion engines do, in fact, give off emissions that are bad for the environment. But, as was said above, spark plugs that don’t work right can damage the catalytic converter, which causes a lot of pollution.

Platinum, palladium, and rhodium are some of the precious metals that are used in a catalytic converter to filter out nearly all harmful emissions. It turns nitrogen oxides, hydrocarbons, and carbon monoxide into less dangerous gases by reducing and oxidizing them.

So, you can see that if you don’t change your spark plugs when you should, you might leave a bigger carbon footprint every time you drive.

Issue #4 – Unstable Idling

When the engine doesn’t fire right, it causes a lot of problems. If a spark plug doesn’t fire or fires at the wrong time, fuel might not get burned.

Since combustion happens several times per second, each misfire causes a sudden loss of power. After that, the spark plug might fire correctly on the next cycle.

So, if you let the engine run while it’s idling, this on/off firing on each cylinder makes it run rough and uneven. You might hear a jittery sound and notice that the RPM is lower than usual. It will feel like your car is fighting for its life.

Issue #5 – Slow Acceleration

Slow Acceleration

Most of the time, slow acceleration in cars with gas engines is caused by the ignition system, and the spark plugs are the usual suspects.

When the engine is misfiring, there are gaps in the power that the pistons make when they move up and down. This reduces the force on the crankshaft, which in turn sends less torque to the wheels.

If your spark plugs aren’t working right, you could lose up to 40% of your car’s acceleration power, which means your gas mileage will be bad.

As you try to make up for the slow speed, you will press down hard on the accelerator pedal, which sends more fuel into the engine

Issue #6 – Rough Revs

Damaged spark plugs can also cause rough revving, which means that when you step on the gas pedal, the engine will sometimes surge and then stop.

If you like going on exciting drives in a loud car, bad spark plugs will ruin the experience for you. If your car doesn’t sound very sporty, it won’t get the attention it deserves.

Also, if you like to show off at car meetups by revving the engine, this problem will make your car sound like it’s sick. Still, the problem could be caused by something else in the ignition system. Most of the time, though, it’s the spark plugs.

Issue #7 – Engine Knocking

Engine Knocking

If the fuel burns unevenly in the cylinders, the engine will knock. In the 4-stroke combustion cycle, the spark should happen at just the right time.

But if one or more pockets of air and fuel mix light at the wrong time, it sends out a shock wave that makes the metallic pinging sound called knocking. The shock wave makes a lot of pressure inside the combustion chamber, which can damage the cylinder walls or pistons, which are very expensive to fix.

You may be wondering how all of this has anything to do with the spark plugs. Well, these parts provide the spark that is needed to start the engine. If they are broken, they could delay the spark, which would make the fuel pockets burn at the wrong time.

If you want to save money, it’s better to keep replacing the spark plugs than to deal with a broken engine, which will cost a lot and take a long time to fix.

Issue #8 – Hard Starts

If your car won’t start, it could be because the gas tank is empty, the battery is dead, or the spark plugs are broken. Spark plugs are what get the whole combustion process going and set it up.

If the spark plugs are broken, you might not get sparks when you turn the engine over. So, it won’t be possible to start the 4-stroke combustion cycle by lighting the fuel.

Remember that trying to start the motor more than once can quickly drain the battery, giving you more problems. It could even cause other problems with the ignition that will cost more to fix.

Even if you can get the engine to start, it will run rough, which could cause it to stop. So, you’ll be back at the beginning.

How To Change Your Spark Plugs

Changing the spark plugs is easiest if you take your car to a mechanic or dealer.

But if you prefer to do things on your own, here are some steps to take.

Take out the spark plugs and cables.

Unscrew the spark plugs that are broken (you can remove all of them for inspection)

Change out the broken parts with the right ones for your car.

Grease the spark plug threads, and then use a torque wrench to screw them back in.

Use a torque chart to make sure they are tightened just right.

Put the cables and coils back on the spark plugs.

Keep in mind that some engines are set up in a way that makes it hard to get to the spark plugs. V-engine cars are especially hard to get to, so you have to know what you’re doing or you might open up the wrong parts.

During the spark plug change, you’ll also need to be very careful that nothing falls into the cylinder. Most of the time, removing it is not a simple task and could cause even bigger engine problems.


Like other parts of a car, spark plugs wear out over time, and if you don’t change them often, a lot can go wrong.

But you can avoid expensive repairs if you follow the service schedule and get them replaced after a certain number of miles.