The spark plug is the final step in the ignition circuit. It accepts a voltage surge flowing from the coil through the distributor, and produces a high-voltage spark that ignites the compressed air/fuel mixture within each cylinder.

In a well tuned engine, supplied with the right fuel, the spark results in smooth, even burning of the compressed mixture. This in turn produces the power to turn the crankshaft. Therefore regular spark plug replacement is one of the surest ways to achieve optimum performance and fuel economy, regardless of what you drive.

Let's follow these easy steps to replace each spark plug in your car's engine:

1. First check and gap the new spark plugs. Check manufacturers' specifications for correct settings. Use a wire type gauge, since it is more accurate, when gapping spark plugs. The wire gauge should slide between the electrodes with a slight drag, Fig. 1. For changing the gap use the handy tool (usually part of gauge set), Fig. 2, to bend the electrode. In removing the old spark plugs it is best to remove and replace one at a time. This will avoid crossing a spark plug wire.


2. Pull the boot off the plug by gently twisting and pulling. Avoid pulling the plug wire away from the boot.


3. Brush any dirt away from the spark plug area that might fall into the cylinder chamber.


4. Remove the spark plug by installing the correct size spark plug socket (usually 13/16 or 5/8 inch), and turning the socket counterclockwise. At the same time apply slight pressure on the socket. This will avoid the socket from stripping on the plug.


5. Now that the plug is removed, compare it to the new plug. Be sure that the reach is the same (threaded area) as well as the overall appearance. Don't hesitate to question any differences. While all spark plugs are basically the same, some differences can cause engine damage if used in the wrong application. Keeping track of the different brand numbers for your car will aid in future purchases.


6. Install the new plug by first placing it into the spark plug socket. Next, by hand, screw the plug into the engine (clockwise). Be careful here not to use force and strip the plug threads. Once threaded a ways begin ratcheting the plug until snug. Don't over tighten. A drop of penetrating oil on the spark plug threads will help avoid cross-threading.


7. Reinstall the spark plug wire. Look for any cracks or other signs of wear. To aid in installing wires use a spark plug boot lubricant. It will also help in making good contact. Also be sure the plug wire is seated. It will usually snap on the plug terminal when properly seated.


8. Follow the above procedure to complete all spark plugs.

Tips: Remember to compare old plugs with the new plugs. Do this to be sure they are correct. Do one at a time to prevent wire mix-up. When removing plugs, be sure there is an insulator boot in side the socket. This will prevent cracking the spark plug insulator on hard to remove plugs. Use penetrating oil to help prevent thread stripping. Remember, new plugs are only as good as the spark plug wires on them. Be sure they are in good shape. The plugs are usually easier to remove when the engine is warm.