Inspecting Your Spark Plugs

*MEDIUM*

Use the following procedure to inspect your spark plugs:

  1. Park the vehicle on level ground with the engine OFF, the parking brake engaged, and the transmission in PARK (for automatic) or REVERSE (for manual). If the engine has been run recently, let it cool. Raise the hood. Cover the battery terminals with a heavy cloth in order to prevent accidental short circuiting the battery with any tools.
  2. It may be necessary to first remove items such as the air cleaner or heat stove duct to provide unobstructed access to some spark plugs. Examine the layout of your engine compartment to determine if such is the case. If so, remove the obstructing component.
  3. Clean the dirt and grease from around each spark plug. Use a rag first, then blow away any loose dirt with a can of compressed air or air from a bicycle pump. Loose dirt must not accidentally enter the combustion chamber during the plug inspection, or engine life will be tremendously shortened.
  4. Disconnect one spark plug wire by grasping the wire boot over the spark plug terminal and pull it with a twisting motion. Do not pull by the wire itself or the boot connection will be damaged.
  5. Use the appropriate sized tool, usually a 5/8" or 13/16" U.S. (or 14 mm or 18 mm metric) wide spark plug socket, to remove the spark plug in a counterclockwise direction. Be sure the socket fits squarely over spark plug shell, or the insulator might become cracked during removal. Use the ratchet handle only to loosen the spark plug; finish removing it by hand. Mark the spark plug and associated spark plug wire with masking tape and the same number.
  6. Repeat the step above for all spark plugs, but label each plug and wire pair with a different number. Use a numbering system that will permit the plug wires to be attached to their correct cylinders after they have all been disconnected. Leave the spark plug wires attached to the distributor cap to avoid a connection mix-up.
  7. Visually inspect or "read" the condition of the spark plugs.
  8. If a spark plug is damaged, fouled or worn, replace it with a new one, but also correct the cause of the faulty spark plug. Otherwise, the existing spark plugs can be reused if they are in good condition. However, clean any deposits with a wire brush and check the gap with a wire feeler gauge before putting the plug back into the engine.
  9. Hold the plug by its terminal. Insert it into the correct socket (cylinder hole) with a gentle clockwise turning motion until the threads grab. If the socket is difficult to access by hand, attach a small piece of rubber tubing to the spark plug terminal to help maneuver it into place and get the threads started. Do not lubricate the threads with grease or oil. This will permit excessive tightening that could strip the threads. Also, do not start threads with socket wrench; if the plug is misaligned in the socket, the threads will be stripped.
  10. Tighten the spark plug as much as possible by hand. Finish tightening an extra quarter turn with the socket wrench if the plug has a metal gasket. If the plug does not have a metal gasket, tighten it an extra 1/16th turn. Double check your owner's manual for correct torque (usually about 10 ft.-lb.); use a torque wrench if necessary. Apply a thin film of dielectric compound to the interior of the associated wire boot using a cotton swab. Also apply some to the ceramic (white) portion of the installed plug. Firmly snap the spark plug boot in place on top of the plug terminal. Push the spark plug wire to its appropriate slot on the wire support bracket.
  11. Repeat the previous three steps for each remaining spark plug. The plugs should be inserted into the same cylinders from which they were removed.
  12. Check your connections by starting the engine. If the idle is rough, confirm that all spark plug wires are connected properly. Close the hood.

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