Symptoms of Bad or Failing Spark Plugs

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Cost of Replacing Bad or Failing Spark Plugs

Common signs of faulty spark plugs include slow acceleration, loss of power, poor fuel economy, engine misfires, and difficulty starting the car. Our certified technicians can come to you and diagnose the problem. You will receive a $30 credit towards any follow-up repairs that result from the diagnostic. Following are example prices for Spark Plug Replacement. Click on the button below to get an upfront quote for your car.

Cars Estimate Parts Cost Labor Cost Savings Average Dealer Price
2003 Chevrolet Silverado 2500 $171 $66.08 $105.00 24% $227.33
2005 Pontiac GTO $144 $74.00 $70.00 20% $181.50
2013 Scion xB $114 $44.40 $70.00 24% $151.90
2012 BMW 740Li $287 $181.92 $105.00 16% $343.17
2003 BMW X5 $381 $255.47 $126.00 15% $448.97
2007 Jaguar X-Type $224 $77.00 $147.00 26% $302.75
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How to Diagnose 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 that is 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 that their spark plugs are replaced every 30,000 to 50,000 miles. However, some newer cars, trucks and SUV's have advanced ignition systems that ostensibly make spark plug replacement unnecessary. Regardless of any warranties or claims made by a vehicle manufacturer, there are still situations where a spark plug wears out or shows signs of failing.

Listed below are a few common symptoms of worn out spark plugs or spark plugs that have fouled and need to be replaced by a ASE certified mechanic as soon as possible, so you can continue driving your vehicle without issue.

1. Slow acceleration

The most common cause of poor acceleration on 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 just as simple as a worn out spark plug. A spark plug is composed of materials that work together in order 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 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

When a spark plug works correctly, it 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 functioning optimally, it is frequently due to the fact that 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 a reduction in fuel economy, 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. Most of the time in modern cars it's 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.

Because of all the potential problems associated with engine misfiring issues, you should contact a mechanic as soon as you notice an engine misfire. A professional mechanic can inspect the issue and determine the right course of action to repair the problem.

4. Difficulty starting the vehicle

If you have trouble starting your vehicle, it could be a sign your spark plugs are worn. However 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, the reality is that spark plugs will eventually wear out. Being proactive about spark plug maintenance can extend the life of your engine by hundreds of thousands of miles.

Misfire
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Matt

12 years of experience
112 reviews
Matt
12 years of experience
Matt showed up on time and got right to work, he was very professional and finished sooner than the estimated time to complete. We will definately be using him again.
2011 FORD F-150 - SPARK PLUG REPLACEMENT - RENTON, WASHINGTON

Theodore

13 years of experience
726 reviews
Theodore
13 years of experience
Theodore was professional, thorough and knowledgeable. He did a great job on the 80k service on my VW and did it for $200 less than the dealer. I will use Theodore again and recommend him to my friends and family.
2013 VOLKSWAGEN GOLF - SPARK PLUGS - BOTHELL, WASHINGTON

Mila

8 years of experience
22 reviews
Mila
8 years of experience
I found Mila extremely competent and thorough. He was very friendly and highly professional in explaining everything accomplished for me, including a complete examination report on my car. I'm very pleased with his work and will definitely look to him for any future car needs I might have. Would recommend him without hesitation to anyone who needs work on their own vehicle.
2008 SATURN AURA - SPARK PLUG REPLACEMENT - RESTON, VIRGINIA

Jamahl

17 years of experience
653 reviews
Jamahl
17 years of experience
Excellent communication regarding delays with getting equipment. Did a great job, and reasonable cost.
2014 PORSCHE CAYENNE - SPARK PLUGS - WINTER GARDEN, FLORIDA

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