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How to Replace Spark Plugs

Using the right tools, almost anyone can deal with this maintenance item. Spark plugs should be changed every 30,000 miles, usually when your car is getting a major tune-up. If your car has faulty spark plugs you will experience trouble starting the car.

Difficulty:
Moderate

Instructions

Things You'll Need

  • Spark Plug Gapping Tools
  • Socket Wrenches
  • Spark Plug Sockets
  • Car Manuals
  • Socket & Ratchet Sets
  • Socket Sets
  • Spark Plugs

  1. Removing the Old Spark Plugs

    • 1

      Pull the hood release lever located under the dashboard.

    • 2

      Walk around to the front of the car, reach under the hood, find the latch and squeeze it. Open the hood.

    • 3

      Find the spark plugs, located in a row along one side of the engine (on an in-line 4-cylinder engine) and attached to thick wires, called spark plug wires. Cars with V-shaped engines (which can have 4, 6 or 8 cylinders) will have spark plugs and spark plug wires on both sides of the engine.

    • 4

      Change 1 spark plug at a time, always putting the plug wire back on before changing the next spark plug (see warning below).

    • 5

      Pull off one spark plug wire where it attaches to the plug. There is a little rubber boot at the plug end of the wire; pull on this part. Pulling higher up on the wire can damage the spark plug wire and cause it to separate.

    • 6

      Blow or wipe away any dirt or debris around the spark plug. You do not want anything to fall into the cylinder while the spark plug is out.

    • 7

      With the spark plug socket and a ratchet, remove the spark plug by turning it in a counterclockwise direction. You may need an extension for your ratchet if the spark plugs are deep-set or not directly accessible. Ratchets with flexible heads are especially helpful for hard-to-reach spark plugs.

    • 8

      Check the spark plug to make sure it needs replacing. A good spark plug should be lightly coated with greyish brown deposits. If heavy deposits are present, if the spark plug is black or if the electrode or core nose are damaged, the plug needs to be replaced.

    Gapping the New Spark Plugs

    • 9

      Find the chart listing the proper "gap" for your plugs in your car's repair manual. The spark plug gap may also be on the sticker on the inside of the car's hood. The parts store can provide you with this specification as well.

    • 10

      Insert the spark plug gapping tool in the gap between the metal center electrode and the metal side electrode of the plug's tip.

    • 11

      Look at the tool's ruled edge and find the gap's measurement. If it is too big, bend the spark plug's end with the tool to widen the gap. To make the gap smaller, push the side electrode (the metal part at the very top) against a hard service.

    • 12

      After adjusting, measure again. Repeat this procedure until the gap matches the specification listed in your car's manual.

    • 13

      Repeat with each plug.

    Installing the New Spark Plugs

    • 14

      Hand-tighten each spark plug in place. If you feel any resistance, stop and start over to prevent cross-threading.

    • 15

      Tighten the plugs with a socket wrench until snug. Do not overtighten.

    • 16

      Replace the spark plug wires. Usually, you will hear a soft pop when the plug wire snaps onto the plug.

    • 17

      Start the engine. Listen. If the engine runs roughly or doesn't start, make sure the wires are pushed all the way onto the new plugs.

View all 45 Comments

Comments

  • pgrandstaff Mar 06, 2010
    As mentioned above, the amount of torque - or how tight you tighten - on the plug is important. On the back of my NGK 4-pack of spark plugs is a chart detailing the proper torque to apply. If you don't have a torque wrench use the column titled "Hand Tight +" which tells you how far to tighten past hand tight. Using Anti-Seize compound on the threads will help protect them. Also, dielectric grease should be applied to the insulated part of the plug and the wire boot to maintain a good, dry and clean connection. If you're unsure of any of the steps, just ask at the auto-parts store. They have always been extremely helpful in my experience.
  • azfab4 Apr 23, 2009
    This was EXACTLY what I was looking for.
  • w1z111 Feb 03, 2009
    Thanks, LorilynFarms...yeah, I know you're right about the pictures. They always help. Thanks for the feedback!
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