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A spark plug is a precision-manufactured electrical device that passes a very high voltage pulse across two electrodes. The ignition system in your car generates very high voltage, as much as 50,000 volts. As that high voltage flows to each plug, the path to ground is interrupted by the spark plug gap, which varies depending on the engine. The voltage is high enough to jump that gap gauge and ignites the air-fuel mixture created. Like all engine components that operate in synchrony, the spark at each spark plug is timed to maximize power and efficiency and also to keep engine emissions as low as possible.
If a spark is found to be faulty, it should be replaced, since it can cause any number of unfavorable symptoms, such as:
Even if only one spark plug is found to be faulty, it is common to replace them all at that time.
Spark plugs are threaded into the engine’s cylinder head(s). Most cars have one plug per cylinder, so a four-cylinder engine will have four plugs, a six-cylinder engine will have six plugs, and so forth. Not all the steps below apply to all cars, but the replacement procedure is as follows:
Yes, but spark plugs that are worn enough to cause engine-misfiring have the potential to cause engine damage and overheating of the catalytic converter. Generally, plug misoperation will not cause the engine to fail to run, but in cases of extreme wear, you may experience a limitation in the speed at which you can operate. If the maintenance schedule says the plugs should be replaced, it is best to do so promptly. Regardless of the age of the plugs, or elapsed mileage, if the engine misfires or runs poorly, the plugs should be inspected for defects.
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