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What you will need:
3/8 drive Spark plug socket, extension and ratchet
New set of spark plugs
Spark plug gaping gauge
Rag or brush
Length of 5/16" vacuum line about 12" long
Why replace your spark plugs?
Spark plugs are one of the most important parts of your vehicle's engine. Your
spark plugs should be replaced every 2 years or 30,000 miles to maintain maximum fuel economy and peak engine performance.
This may vary depending on the make and model of your vehicle. Some models will go as far as 100,000 miles before the plugs
need replacement. Replacing your spark plugs isn't that difficult but, be sure to read all the instructions listed below.
Before you start:
Get all the tools you'll need and gap your spark plugs. The proper spark plug gap can be found
on the engine specifications decal under the hood. Get the right plugs for your car. I always recommend using the brand of
plugs originally installed in your car from the factory. For Ford products they are Motorcraft , General Motors products use
AC Delco and in Chrysler products they are Champion. In Japanese cars I would use NGK and in German cars I would use Bosch.
Consult a parts guide to get the correct spark plugs. A cross reference will not often get you the exact plug you need.
Okay, let's get to work.
Always change your spark plugs with the engine cold. Grabbing the plug wire by the
boot, carefully pull the spark plug wire from the end of the spark plug. Do not pull the wire itself. If the boot sticks,
twist the boot left and right and pull the plug wire off. I would recommend changing the plugs one at a time to avoid mixing
up the spark plug wires.
If you have it, use compressed air to blow any dirt away from the spark plug area. Otherwise,
clean off the old plug and the area around it with a rag or small brush. This will help prevent any foreign material from
falling into the cylinder when the plug is removed.
Remove the plug by turning it counterclockwise with a spark plug socket
and ratchet. Once you crack it loose, spin it out about three or four turns. Then remove the socket and remove it completely
by hand. If you can't reach it, use an extension on the spark plug socket or slip the 5/16" vacuum line over the spark plug
and turn it out with that.
If you haven't done so yet, gap the new plug with a spark plug gap gauge (The proper gap can
be found on the engine specifications decal under the hood). Slip the correct thickness wire or feeler between the inner and
outer electrodes at the tip of the plug. A flat gauge is good; the wire type is better. When the plugs are properly gapped,
the wire or feeler should slide between the electrodes with a slight drag. If the gap is incorrect, gently bend the outer
electrode slightly until the correct gap is achieved. Make sure that the outer electrode is centered directly over the inner
electrode. If it's not, align the two by gently bending the outer electrode
Take a good look at the cylinder head threads.
They should be in good condition, clean, and free of dirt and debris. This new spark plug should freely screw into the cylinder
head by hand. Any binding of the plug is an indication that there's a problem. Remove the plug and inspect the threads.
Insert
the plug into the spark plug hole by hand and turn it clockwise until it's snug. I usually attach a short piece of 5/16" rubber
hose to the top of the plug and use it as an extension to install the new plugs. I can feel if the spark plug is threading
down correctly. Starting the plug using the spark plug socket may cause you to cross thread the plug and cause damage to the
cylinder head.
After installing the plug by hand as far as it will go, firmly tighten it with a spark plug wrench or socket.
It's a good idea to use a torque wrench, if one is available, to ensure that the plug's properly seated. Be very careful;
do not over tighten the spark plugs. Remember, you'll get an accurate torque reading only if the spark plug and cylinder head
threads are clean and dry.
Reattach the plug wire to the new plug. Use a twisting motion on the boot until it's firmly
seated on the top of the plug. You will feel and hear a click as the wire clamps onto the spark plug.
Repeat these same
steps for the other plugs. If you take your time this is a fairly easy job and will probably take you about an hour, depending
on how many plugs your vehicle has.
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