How to Tell If My Car Needs New Spark Plugs

by William Zane
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The spark plugs in your engine are essential components that ensure that the engine receives a reliable spark for fuel combustion. If spark plugs become old and fouled, the car’s engine will not run as well as it should. Installing new spark plugs is usually considered part of a tuneup on a car’s engine. Spark plugs generally last 12,000 to 15,000 miles and should be inspected regularly and replaced if they have become fouled or damaged.

Step 1

Pay attention to how the engine in your car is running. If the engine is missing or hesitating, it may need new spark plugs. When an engine has a miss, it is not firing on all of its cylinders and will not produce as much power as it normally does and will not run as smoothly as it is supposed to. Other symptoms include a rough and uneven idle. Though a miss or rough running is not always caused by bad spark plugs, they can be one of the causes. Bad plugs can also cause the car to emit more pollutants than normal and even contribute to it failing to pass emissions testing.

Step 2

Find out if your gas mileage is suffering. In addition to poor running, bad spark plugs can also cause poor fuel mileage. Compare your current fuel mileage with the fuel mileage your vehicle usually returns. If you’re filling up at the pump more than you normally do, it may be because you need new spark plugs.

Step 3

Remove your plugs to inspect them. This is one of the most effective ways to determine if you need new spark plugs. Remove the spark plug wires by pulling them off of the plugs. If your vehicle is equipped with a coil-over-plug setup (instead of spark plug wires) unbolt the coils and remove them from the spark plugs. Remove the plugs with a spark plug socket by placing the socket over the plug and loosening it.

Step 4

Inspect the plugs. Spark plugs that are functioning properly should be dry and free of oil and should have a grayish-tan color and exhibit slight but not excessive wear on the electrode. If they are wet from fuel, they are likely fouled and will need to be replaced. If they are black and sooty, they will need to be replaced and the cause of the plug’s fouling will need to be determined.

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