National average cost of a Spark Plug Replacement for popular vehicles:
Avg. cost $70
Avg. cost $92
Avg. cost $104
What is a spark plug and how does it work?
A spark plug is an integral part of your vehicle's ignition system. It is critical to the combustion process inside your engine.
An internal combustion engine houses hundreds of components that work in concert to produce the power needed for your vehicle to move. Anywhere from four to eight pistons move up and down constantly in their respective cylinders, pedaling the crankshaft like you might pedal a bicycle.
A lot of energy is required to keep these pistons moving. So, every other time a piston rises in its cylinder, it compresses a precise mixture of air and fuel. At just the right time, a spark plug ignites the compressed air/fuel mixture, resulting in the rapid release of energy. The expanding gasses that are produced move the piston downward toward the crankshaft.
The spark plug itself delivers a tiny yet high-voltage electrical arc in response to the ignition coil. Each cylinder needs a spark plug for ignition. Some engines use two spark plugs per cylinder. Spark plugs are typically replaced as a complete set.
How do I know if my engine needs new spark plugs?
There are several problems that can occur if your spark plugs are worn out, and several signs that that is the case. Symptoms of bad or failing spark plugs include
Your engine has trouble starting
Rough idle or engine vibration
Loss of engine power
The engine stalls
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Spark plug replacement is not a particularly complicated service, but it can be quite difficult on some engines. That is because access to the spark plugs is often limited and requires special tools. And if a spark plug breaks before it comes loose from the cylinder, the repair can be significant.
The specific process for replacing spark plugs also differs depending on the age of your vehicle and the type of ignition coil(s) used. Older models featured a distributor that controlled the way each spark plug was fired, the timing between cylinders. On those engines, spark plug wires extended from the distributor cap to each spark plug. Some newer models with electronic ignition rely instead on a set of coils that get their direction from the engine control module. Spark plug wires, in those cases, run from the coils to the spark plugs. The latest technology includes coils that are installed directly on top of each cylinder and spark plug in an arrangement known as “coil-on-plug” or COP.
To remove and replace the spark plugs, a technician must do the following
Disconnect the negative terminal on the battery, taking care to preserve the computer memory in the vehicle
Unplug the ends of the spark plug wires from each spark plug or unplug the coil connectors (in the case of COP) and unbolt and dislodge the coils from the plugs
Clean out the holes where the spark plugs are mounted so that debris does not enter the cylinders
Using a special socket, unscrew the spark plugs and extract them from their mounts
Using a feeler gauge, check the gaps between the two electrodes on each spark plug to ensure that they are set to manufacturer’s recommendations and adjust if necessary
Insert the new spark plugs and torque to manufacturer’s specifications
Reinstall the spark plug wires or coils and connectors
Reconnect the battery
It is common to also replace either the spark plug and coil wires (older models) or the coil boots (newer models) when replacing a set of spark plugs.
OTHER QUESTIONS CUSTOMERS ASK
Can I replace a spark plug myself?
There was a day when spark plug replacement was a simple task, part of routine vehicle maintenance that most vehicle owners could perform. With changes in technology, including the transverse engine found in most front-wheel-drive vehicles (where the engine is mounted sideways), the job has become more difficult to perform. In some cases, much more difficult. A person armed with a spark plug socket, a ratchet, and a set of feeler gauges might be able to change out a set of spark plugs. But it is really tough to get to some spark plugs without specialty tools.
Do spark plugs come pre gapped?
Most spark plugs today are manufactured to specific specifications for your vehicle. Where, in the past, it was necessary to adjust the gaps between electrodes on each new spark plug, today plugs come pre gapped. That said, it is still necessary to check the gaps on all new spark plugs to ensure that they are correctly set to the manufacturer’s recommendation before installing them.
What happens when spark plugs go bad?
When a spark plug goes bad, it does not properly ignite the compressed air/fuel mixture inside the cylinder. It misfires. An engine misfire leads to all sorts of issues, including a lack of power, decreased fuel efficiency, and even long-term damage. That is why you might see a check engine light come on when your spark plugs are failing.
What parts are related to a Spark Plug Replacement?