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12 Mar 2011

How To Change Spark Plugs On Your Car

In this guide we are going to show how to change spark plugs on your car and set the electrode gap for the best possible spark. Setting the correct electrode gap is essential for good fuel economy, cold starting and smooth engine idle. Set the gap too wide and the HT (High tension) coil will not provide enough voltage to provide an arc across the gap, possibly resulting in no spark at all. Set the gap too narrow and the spark will be too small.
1. Remove HT lead or coil pack from spark plugPull off the HT lead from the first spark plug by grabbing the rubber boot and pulling sharply whilst taking care not to cut yourself on sharp engine components.

2. Clean around the spark plug
With the spark plug exposed, use a paint brush around the base of the spark plug to brush away dirt which could fall into the cylinder when the plug is removed. If compressed air is available, blow any dust out from around the base of the spark plug left behind by the brush. It is very important not to allow any dirt to enter the cylinder when the spark plug is removed.
3. Remove old spark plug
With a spark plug socket (normally 13/16 or 5/8 deep socket), turn the spark plug counter-clockwise with the socket wrench to remove.
4. Set electrode gap on new spark plugs
Using a spark plug electrode gap tool or feeler gauge, set the gap as recommended by your car manufacture for your engine model. You can sometimes find this information in your car owners/service or Haynes manual. Alternatively, your auto parts store where you purchased the new spark plugs may be able to tell you this.
To set the gap, find the correct size feeler gauge and slide it between the inner and side electrode. If the gap is too wide, tap the side electrode against the inserted feeler gauge with a small hammer. Gently tap until the gauge fits snug between the two electrodes.
If the gap is too narrow, prise the gap open with a thin feeler gauge and follow the above until the gap reduces to the correct width.
5. Fit new spark plugs
You should now be able to screw the new spark plug in place by hand. If there is too much resistance, unscrew the spark plug and try again. You should not screw the spark plug in with the socket wrench as this can damage the aluminum thread which is very soft and easy to cross thread.
When the spark plug cannot be tightened any further by hand, attach the socket wrench and turn clockwise a quarter of a turn using just one or two fingers, taking care not to over-tighten.
6. Refit HT leads to spark plugs
Push the HT lead for the spark plug back on and you should hear a pop where the clip in the wire plug snaps onto the top of the spark plug.
Continue with repeating steps 1 through to 6 for each additional cylinder. It is important to ensure only one HT lead is removed at any one time. This is to ensure the firing order is not changed.

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