Spark plugs
Small parts in a gasoline engine that make the spark to light the fuel, one for each cylinder.
In plain English
A gasoline engine makes power by burning a mix of air and fuel inside its cylinders, the chambers where the pistons move up and down. Each cylinder has a spark plug screwed into it, and at the right moment the plug makes a small electric spark that lights the mix. The electricity for that spark comes from the ignition coil. Over time the metal tips of the plugs wear away or get coated with deposits, and the spark gets weaker.
Why it's on your estimate
Spark plugs are a wear item, so a shop may recommend new ones as scheduled maintenance; check your owner's manual for when they are due. A shop may also recommend them when worn plugs are causing trouble, such as a rough or shaky idle, hard starting, sluggish acceleration, worse fuel economy, or a misfire, which is when a cylinder fails to fire properly and may turn on the check engine light.
How urgent is it?
Fix soon
Worn plugs usually get worse gradually, so there is normally time to plan the work, but the engine will run less smoothly and use more fuel in the meantime. It becomes more serious if the engine is misfiring, and a flashing check engine light means you should get it checked right away, because ongoing misfires can damage the catalytic converter.
Questions to ask the shop
- Are the plugs due by the schedule in my owner's manual, or did you find a misfire or other problem?
- Can you show me the old plugs and what you see on them?
- If there is a misfire, have you checked the ignition coils and other possible causes as well?
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