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8 Common Problems If You Don’t Change Your Spark Plugs!

8 Common Problems If You Don’t Change Your Spark Plugs!

Spark plugs are critical components in a gas engine’s internal combustion system. They are responsible for converting the electrical signal they receive from the ignition coil to a spark to ignite the air-fuel mixture in the combustion chamber.

Over time, these components wear off due to extreme temperatures, debris, and regular wear and tear. When this happens, you will notice your engine misbehaving, so you must follow the recommended changing schedule by the manufacturer.

Spark plugs wear out over time and eventually lead to reduced engine performance, malfunctions, failed starts, and emissions issues when not replaced. Spark plugs typically last between 30,000 to 80,000 miles of use and will vary by manufacturer.

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

Issue #1 – Reduced Gas Mileage

The most common issue with faulty spark plugs is an increase in fuel consumption. When spark plugs wear, the gap widens between the electrodes – leading to a high chance of experiencing a misfire.

Similarly, soot might form between these contacts and increase the chances of not producing a spark.

If this occurs, the air-fuel mixture will get injected into the combustion chamber and exit without being ignited. As such, the vehicle will consume more fuel but produce little power. You have to put more pressure on the gas pedal to get enough torque.

Faulty spark plugs can increase fuel consumption by up to 30%, which means you will spend more at the gas pump when refilling.

Issue #2 – Engine Backfire

An engine backfire occurs when the combustion or explosion of the air-fuel mixture takes place outside of the combustion chambers. In some cases, the backfire goes up the intake valve, leading to the destruction of parts of the engine.

In most cases, though, it goes out through the exhaust, which causes a flame to pop out of your vehicle’s tailpipe when you rev the engine.

One of the causes of this problem is worn-out spark plugs. Since they won’t produce the spark at the right time or produce it at all, the fuel mix will not get ignited. Instead, it will exit the cylinders while still flammable when the exhaust valves open.

If the mix ends up burning through the exhaust system, it might look cool with the flame back there, but this will cause damage to the catalytic converter. Replacing this component is no joke!

A catalytic converter is expensive and can set you back over $1,000, so it is better to change the spark plugs on time.

Issue #3 – Harmful Emissions

Of course, internal combustion engines produce emissions that are not good for the environment (CO2). However, as stated above, faulty spark plugs can cause damages to the catalytic converter, leading to excessive pollution.

A catalytic converter uses precious metals like platinum, palladium, and rhodium to filter out harmful emissions to nearly zero. It converts nitrogen oxides, hydrocarbons, and carbon monoxide through reduction and oxidation to less toxic gases.

So now you can connect the dots – if you don’t change your spark plugs as required, you might leave a larger carbon footprint on the environment every time you drive.

Issue #4 – Unstable Idling

Misfiring causes a lot of problems in the engine. If a spark plug does not fire or does it at the wrong time, fuel might not get burned.

Since the combustion process occurs several times every second, each misfire creates a sudden loss of power, after which the spark plug might fire accurately during the next cycle.

Therefore, if you leave the engine idling, this on/off firing on each cylinder causes rough, uneven running. You might notice a lower RPM than usual, strong vibrations, and a jittery sound. It will be as if your car will be struggling to stay alive.

Issue #5 – Slow Acceleration

The most common problem with slow acceleration in automobiles with gas engines is the ignition system, with the usual suspect being the spark plugs.

Misfiring causes gaps in the production of up and down power by the pistons, which, in turn, reduces rotational force on the crankshaft and causes low torque to get to the wheels.

Faulty spark plugs can cause up to 40% loss in acceleration power, and with this comes poor fuel economy!

As you try to compensate for the slow acceleration, you will floor the accelerator pedal, which directs more fuel into the engine.

Issue #6 – Rough Revs

Another issue that arises with damaged spark plugs is rough revving, whereby the engine will go through phases of surging and hesitation as you step on the gas pedal.

If you love going on thrilling drives with a loud car, faulty spark plugs will ruin the experience for you. Your vehicle will not get the attention it deserves because it won’t sound very sporty.

Also, if you like attending car meetups to show off by revving the engine, this issue will make your vehicle sound sickly. That said, the problem might originate from other parts of the ignition system. But in most cases, it is the spark plugs.

Issue #7 – Engine Knocking

An engine knock occurs when fuel burns unevenly in the cylinders. Ignition should take place at just the right moment in the 4-stroke combustion cycle.

However, if one or more air-fuel mix pockets ignite at the wrong time, it creates a shock wave that produces the metallic pinging sound known as knocking. The shock wave creates a lot of pressure inside the combustion chamber and can damage the cylinder walls or pistons, which are very expensive to repair.

You might be wondering how all this connects to the spark plugs. Well, these components deliver the spark required for ignition. If they are faulty, they might delay the production of the spark, which will cause the fuel pockets to burn at the wrong time.

Economically, it makes more sense to replace the spark plugs regularly instead of dealing with a damaged engine, which will dent your pocket and take a lot of time to repair.

Issue #8 – Hard Starts

If you are having trouble starting your car, it could be an empty gas tank, a dead battery, or faulty spark plugs. Spark plugs are responsible for launching and setting up the whole combustion process.

Damaged spark plugs might not produce sparks as you crank the engine. As such, it will not be possible to ignite the fuel and start the 4-stroke combustion cycle.

Remember that trying several times to start the motor can drain the battery quickly, leaving you with more problems. It might even cause other ignition issues that will cost more money to fix.

Even if you get the motor to power on, rough idling will ensue, and this might cause stalling. Therefore, you will end up in square one.

How To Change Your Spark Plugs

The easiest option is to take your car to the mechanic or dealer to get the spark plugs changed.

However, if you like doing things on your own, here are a few steps to follow.

  • Remove the ignition coils and cables
  • Unscrew the damaged spark plugs (you can remove all of them for inspection)
  • Replace the damaged pieces with the right ones that fit your car
  • Lubricate the spark plug threads, then screw them back in using a torque wrench
  • Use a torque chart to ensure that they are perfectly tightened
  • Fix the ignition coils and cables back on the plugs

Keep in mind that some engine configurations make it a bit difficult to access the spark plugs. The V-engine models are particularly hard to reach, so you must know what you are doing to avoid opening up the wrong parts.

You’ll also want to be extremely careful to not let any debris fall into the cylinder during the spark plug change. Removing it is not a trivial ordeal in most cases, and could lead to even bigger engine issues!


Like other car components, spark plugs wear out eventually, and a lot can go wrong if you don’t change them regularly.

However, if you stick to the servicing schedule and get them replaced after covering the specified mileage, you will avoid expensive repairs!

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Zach Reed

Hi, I'm the founder of! Having owned a wide variety of vehicles in my life, I was astounded at how hard it can be to find answers to common automotive questions. Rather than sit idly, I decided to create this website to help others!