How to tell if spark plugs need to be changed?

Author: Charley Rutherford II  |  Last update: Thursday, July 2, 2026

5 Signs You Need New Spark Plugs
  1. Engine Misfires. A misfiring engine is a big sign that one or more of your spark plugs are not firing properly. ...
  2. Poor Gas Mileage. When spark plugs are working correctly, they burn fuel efficiently in your engine. ...
  3. Trouble Starting. ...
  4. Slow Acceleration. ...
  5. Rough Idling.

What are the symptoms of bad spark plugs?

What are the signs your Spark Plugs are failing?
  • Engine has a rough idle. If your Spark Plugs are failing your engine will sound rough and jittery when running at idle. ...
  • Trouble starting. Car won't start and you're late for work… Flat battery? ...
  • Engine misfiring. ...
  • Engine surging. ...
  • High fuel consumption. ...
  • Lack of acceleration.

How do I know if spark plugs need replacing?

Here are seven signs that are telling you that you need spark plug replacement on your vehicle.
  1. Your Vehicle is Difficult to Start. ...
  2. Your Engine is Misfiring. ...
  3. You Have Poor Fuel Economy. ...
  4. Your Engine Idles Rough. ...
  5. Your Car Doesn't Accelerate Easily. ...
  6. Your Engine is Loud. ...
  7. Your “Check Engine” Light Comes On.

How much does it cost to replace spark plugs?

If you drive a compact car with a four-cylinder engine, an average set of platinum spark plugs will cost you about $32 or so. A six-cylinder will cost around $48, and a V8 will be around $64 for the parts alone.

What will happen if spark plugs are not replaced?

As spark plugs wear the spark will get weaker and the chances of poor ignition or a misfire (no ignition) go up. This will cause decreased power, worse fuel economy, worse emissions, and can damage other parts like the catalytic converters.

Symptoms of Worn Spark Plugs and When it's time to replace it

Will I notice a difference after changing spark plugs?

Smooth Engine Start-Ups: You can feel the difference new vs. old spark plugs make when you start your vehicle. New spark plugs allow the engine to start almost effortlessly.

What does a misfire feel like?

Every motorist has experienced a misfire at some point. It usually shows itself in the form of stutter, shudder type feeling, slower acceleration and loss of power. An idling car might vibrate a little more than usual in the event of a misfire.

Can I drive with bad spark plugs?

Can You Drive with Faulty Spark Plugs? Faulty spark plugs can lead to a range of issues that can cause long-term damage to your engine. If left unchecked, bad spark plugs can even lead to more expensive repairs, such as replacing the catalytic converter, so don't put it off.

Is changing spark plugs an easy job?

Whether you can change the spark plugs yourself depends on how convenient they are to reach. With older vehicles, the job is relatively easy and needs only some wrenches and a new set of spark plugs. You can easily find instructions in your owner's manual or online.

What does a tune up consist of?

An oil change and oil filter change, tire rotation, cabin air filter, brake inspection, transmission fluid change, and coolant-system flush may also be on the agenda. Check Kelley Blue Book Maintenance Schedules or your owner's manual for your manufacturer's recommended service intervals for all systems.

Why does my car run worse after changing spark plugs?

This can be a sign of spark plugs that are not properly gapped or of poor quality. Loss of Power: The car may experience a significant loss of power, making acceleration sluggish and overall performance lackluster. This can occur if the new spark plugs are of lower quality or not the correct type for the vehicle.

When replacing spark plugs, what else should be replaced?

COP coils and their insulator boots are made of plastic and rubber that protect and insulate the high voltage conducting materials inside. Damage will cause the high voltage to leak (short) to ground causing a misfire and possible damage to other ignition components. If the boots are damaged they must be replaced.

What are the symptoms of a dirty fuel filter?

Symptoms of a Clogged Fuel Filter
  • Difficulty starting. A diesel engine that does not receive adequate fuel can be hard to start.
  • Engine misfiring. ...
  • Rough idling. ...
  • Poor engine performance. ...
  • Poor fuel economy. ...
  • Whining and unusual sounds.

How do I know if I need to replace a spark plug?

The most common signs of bad spark plugs include start-up trouble, rough idling, sluggish acceleration, declining fuel economy, engine misfiring, and engine knocking.

What does a misfire sound like?

Engine misfires have a very distinct sound that can make them easier to diagnose than other car problems. Popping, sneezing, or banging sounds coming from the exhaust are a sign of a misfire. This sound comes from the unburnt fuel leaving the cylinder that combusts through the exhaust system.

Will my car run better if I change the spark plugs?

Over time, spark plugs may become clogged or damaged, resulting in decreased engine performance. Changing your spark plugs can help to keep your engine running smoothly and efficiently. In addition, they can also help to improve fuel economy and reduce emissions.

How long should it take a mechanic to change spark plugs?

It will take about one hour to replace your spark plugs for a four-cylinder engine. A V6 and V8 may take longer than an hour. Changing a vehicle's spark plugs is a DIY thing, but it may sometimes get complicated.

How often should I replace ignition coils?

If your vehicle's fuel-to-oxygen mixture is either rich or lean, therefore, your ignition coils may fail prematurely. Additionally, engine heat and vibrations can cause damage to ignition coils. Nevertheless, on most vehicles can go 80,000 to 100,000 miles before requiring an ignition coil replacement.

What are the symptoms of old spark plugs?

Your driving habits also play a crucial role in spark plug wear. If your car shows any of the faulty spark plug symptoms mentioned earlier, such as difficulty starting, rough idling, decreased fuel efficiency, or misfires, it's a sign you need to replace your spark plugs.

Can I replace spark plugs myself?

The answer depends on the type of engine in your vehicle. Some V-6 models require removing portions of the intake manifold to replace the spark plugs. If you're not comfortable with that, take your vehicle to a pro. But if your engine affords easy access to the rear bank, you can probably do the job yourself.

How long can you run with bad spark plugs?

How long can you drive with bad spark plugs? Ideally, you should replace them immediately.

Can low oil cause misfire?

Engine misfires are caused by many things, including: Dirty, broken or worn-out spark plugs. Low oil pressure (injector clogging) and/or overheating issues. Engine parts that aren't fitted correctly.

What are the symptoms of a bad ignition coil?

The signs below from your Lexus dealer will warn you when it's time for repairs to avoid engine damage and expensive repairs.
  • The Check Engine Light Is On. ...
  • Your Car Feels Slow. ...
  • Your Car Is Heavy on Gas. ...
  • Your Car's Engine Misfires. ...
  • Your Car Backfires. ...
  • You Struggle with Starting and Stalling Issues. ...
  • You Hear Sputters and Coughs.

Is a misfire expensive to fix?

Depending on the cause of the problem, an issue with a misfiring cylinder can be fairly expensive. For something like a faulty spark plug, repair work should only cost somewhere in the range of $150 to $400. For something more serious, like a blown head gasket, costs can shoot up into the thousands of dollars.

Previous article
How long does it take for toilet tissue to decompose?
Next article
What is the best type of exterior dryer vent?