1. Home
  2. Articles
  3. Symptoms of Bad or Failing Spark Plugs

Symptoms of Bad or Failing Spark Plugs

failing spark plugs

Without a spark, there would be no way for fuel to ignite in the combustion chamber. Spark plugs have been a critical component of the internal combustion engine for years. Spark plugs are designed to transmit an electrical signal sent from the ignition coil at a predetermined time to create a spark that ignites the air-fuel mixture inside the combustion chamber. Each vehicle requires a particular type of spark plug made from specific materials and with a designated spark plug gap set by a mechanic during installation. Good spark plugs will burn fuel efficiently, while bad or failing spark plugs can cause the motor not to start at all.

Spark plugs are similar to motor oil, fuel filters, and air filters in that they require routine service and maintenance to keep your engine running strong. Most vehicles sold in the United States require their spark plugs to be replaced every 30,000 to 50,000 miles. However, some newer cars, trucks, and SUVs have advanced ignition systems that ostensibly make spark plug replacement unnecessary. Regardless of any warranties or claims made by a vehicle manufacturer, there remain situations where a spark plug wears out or shows signs of failing.

Listed below are 6 common symptoms of worn-out spark plugs or spark plugs that have fouled and need to be replaced by an ASE certified mechanic as soon as possible.

1. Slow acceleration

The most common cause of poor acceleration in most vehicles is a problem in the ignition system. Today's modern engines have multiple sensors that tell the onboard computer and ignition system when to send electric pulses to fire the spark plug, so the issue may be with a faulty sensor. However, sometimes the issue is as simple as a worn-out spark plug. A spark plug is composed of materials that work together to produce a spark hot enough to ignite the air-fuel mixture. When those materials wear out, the effectiveness of the spark plug is reduced, which can significantly reduce the acceleration of the vehicle.

If you notice that your car is running sluggishly or does not accelerate as quickly as it used to, it may be attributed to a faulty spark plug that needs to be replaced. However, you should contact a mechanic to inspect this issue as it could be caused by multiple other factors including bad fuel filters, dirty or clogged fuel injector, or issues with oxygen sensors.

2. Poor Fuel Economy

A fully-functioning spark plug helps burn fuel efficiently in the combustion cycle. When this occurs, your car can achieve better-than-average fuel economy. When the plug is not working optimally, it is frequently because the gap between the spark plug electrodes is either too close or too far apart. In fact, many mechanics will take out spark plugs, examine them, and adjust the gap to factory settings as opposed to replacing the spark plug entirely. If your vehicle has an increase in fuel consumption, it very well could be attributed to a worn out spark plug.

3. Engine is Misfiring

If the engine misfires, it's typically due to an issue in the ignition system. In modern cars, it's usually due to a sensor malfunction. However, it may also be caused by a spark plug wire or the tip of the spark plug that connects to the wire being damaged. An engine misfire can be noticed by intermittent stumbling or sputtering sounds from the engine. If the engine is allowed to keep misfiring, exhaust emissions will increase, engine power will decrease, and fuel economy will drop.

4. Engine Surging or Hesitating

You may notice the engine hesitating while accelerating. In this case, the engine is not responding correctly to the driver. It may suddenly surge in power, then slow down. The engine is sucking in more air than it should be in its combustion process, causing the delay in power delivery. The combined hesitation and surging could indicate a spark plug problem.

5. Rough Idle

A bad spark plug may cause your engine to sound rough while idling. The vehicle-encompassing, jittery sound will also cause your vehicle to vibrate. It can indicate a spark plug problem in which a cylinder misfires only while idle.

6. Hard to Start

If you have trouble starting your vehicle, it could be a sign your spark plugs are worn. As noted above, the engine's ignition system is comprised of multiple individual components that must work cohesively in order to function properly. At the first sign of problems starting your car, truck or SUV, it's a good idea to contact a certified mechanic to take a look at the cause.

Regardless of what the issue might be, you might end up needing new spark plugs when yours eventually wear out. Being proactive about spark plug maintenance can extend the life of your engine by hundreds of thousands of miles.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Still not sure about your car's issue?
Diagnose your car
What kind of issue are you experiencing?
Brakes are squeaking
Car is not starting
Car is overheating
Car is shaking (vibrating)
Fluids are leaking
Heating and A/C
Smoke or steam is coming out of the car
Warning light is on
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...
How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....

Related questions

Q: I have a 2012 Dodge Charger R/T AWD and I have check engine light issues

Hello, thank you for writing in. The long list of potential issues that cause hard-starts and misfires is profound. Without knowing exactly what diagnostic codes the dealership was pulling from the check engine light, it is impossible to narrow down...

Q: Car starts, but doesn't stay started.

The problem you describe can be the crankshaft position sensor. The sensor is a major failure on these vehicles and can cause no starts or intermittent starts and stalls. Have a qualified mechanic test you car with an approved scanner...

Q: it screams when I push the gas petal to accelerate the rpm rev high causing it to act like its losing power going up hill

This sounds like the transmission is slipping. I recommend having a transmission mechanic diagnose the slipping by checking transmission pressures, checking for trouble codes, or checking for any solenoids that are not letting it shift.