ALT-4 How to Change Spark Plugs
A spark plug has a gap between two terminals. The ignition system creates a high voltage that jumps this gap, creating a spark. Over time the terminals wear and the gap widens, eventually becoming too big for a spark to form. To keep the engine running, spark plugs should be changed before that happens.
It's not difficult to change spark plugs, providing you have a few basic tools and work methodically. Let's start with the tools. You'll need a plug socket of the right size to fit the hexagon on your spark plugs, a ratchet and an extension bar. It's also useful to have a small torque wrench, a spark plug boot puller, (an inexpensive tool available from all auto parts stores,) and a can of compressed air.
With the engine cold, open the hood and locate the spark plugs. On some vehicles it will be necessary to remove the plastic shrouding to get access. The top of the spark plugs will be covered by a black rubber boot with a wire or lead that supplies the high voltage. Never disconnect more than one lead at time because they could get mixed up. The best approach is to begin at one end and work along methodically, replacing one plug at a time.
Pull the boot off the plug by gripping it firmly and tugging upwards. Never pull on the lead as this can damage it. If you can't get your fingers on the boot, (often the case in newer engines,) slide the spark plug boot puller over the boot until it hooks under the bottom edge. Then pull up in a straight line.
With boot removed you should see the top of the spark plug. Before unscrewing it, put on safety glasses and use the compressed air can to blow out any debris lurking in the hole. This ensures that nothing falls in to the combustion chamber.
Now slide the plug socket down over the plug and rotate it slowly until it drops over the hexagon at the base. With the socket seated, turn the ratchet counterclockwise and remove the plug.
Once the plug is out, examine it closely. The appearance of the terminals indicates the condition of the engine. The firing end should be a light brown color. If it's black and oily there's a problem that you need to get checked out. Also compare it with a new plug. The bottom end, from the hexagon down to the firing end, should be the same length. If it's not, you've probably got the wrong plugs.
Carefully insert the new plug into the hole where the old one came from. Screw it in gently by hand, making sure not to get it cross-threaded. If it seems not to want to go in, back it out and try again. It's very important not to force it as that can damage the cylinder head.
Screw the plug in finger-tight then use the torque wrench. Tighten to around 11 to 15 foot-pounds unless the vehicle manual says otherwise. Then push the boot back over the top, making sure it engages with the terminal with a click.
That's the first spark plug done. Now just repeat the procedure for the rest.
