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Spark Plug Replacement

How do spark plugs work?

Spark plugs are the matches that light the fire within the combustion chamber of your car’s engine. An ignition coil receives a small amount of battery power and multiplies it into a high-voltage current. This current travels through the bottom part of the coil to the top portion of the spark plug. The high-voltage current is required to create a spark across an air gap at the bottom of the plug. Air creates resistance and does not conduct electricity well, so more electricity is needed to overcome the resistance. The high voltage package overcomes air, crossing the gap, causing the spark that ignites the fuel air mixture.

How often should you replace your spark plugs?

Spark plug replacement is required at the mileage interval provided in the vehicle’s owner’s manual and should be seen as a normal part of overall preventive care.

This mileage interval can vary greatly from vehicle to vehicle and depends upon the type of spark plug preferred by the manufacturer. Traditional spark plugs are made with a copper central electrode, which provides a suitable heat range for city and highway driving. They tend to last for 30,000 miles before carbon deposits and consumption of the copper electrode lead to inefficient spark jump and misfire. Newer technology spark plugs use a platinum or iridium electrode which is thinner, thus less prone to carbon deposits and consumption. Generally they last for 60,000 miles to 80,000 miles for platinum and 100,000 miles for iridium. Other factors can contribute to premature spark plug replacement. Use of a lower octane gas, a clogged fuel or air filter, or any sensor that the computer uses to meter the fuel to air ration will change the combustion within the cylinder and advance the replacement interval of spark plugs due to carbonization or consumption.

What are the symptoms of a faulty spark plug?

Engine misfire is the first sign of poor spark. Basically, the spark plugs are firing poorly or incorrectly, so combustion is not ideal or controlled. The sputtering or chugging of the engine is a sure sign of misfire, but a noticeable loss of power or a check engine light due to raised emissions are also symptoms.

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How soon should I replace worn spark plugs?

Critical. If spark plugs are not replaced at the correct interval, loss of power, loss of fuel economy, and higher emissions are some of the simpler problems. Further neglect will cause severe decline in engine performance and could contribute to a more costly repair. Instead of contributing to ideal combustion, the spark plug causes poor, uncontrolled combustion with higher levels of unburned fuel sent into the exhaust. The catalytic converter cannot keep up with the unburned or partially burned fuel, and will become permanently damaged and need replacement. Carbonization within the combustion area will become a serious issue. Fuel injectors, valves and cylinders will all become coated with carbon and further complicate the running of the engine. If left untouched, combustion will reach a point where the detonation of the air and fuel mixture happens at the wrong time and will lead to piston and valve train damage that will need significant repair.

What is the typical cost to replace spark plugs?

  • Estimated part(s) and labor cost: $130–$180

Most automotive service professionals can perform this service. Keep in mind, pricing will vary by location and your vehicle make and model. Save time and money by using Openbay to compare pricing and book an appointment with a service center in your area.

Service article written by an ASE Master Technician

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