How to Change the Sparkplugs on a 1998 Ford Expedition
- 1). Disconnect the negative battery cable from the battery using a wrench to loosen the retaining bolt. Lift the terminal off the battery and set the cable aside.
- 2). Remove the spark plug wire from the first spark plug. Grasp the wire at the boot and twist it as you pull it out. Do not remove any other plug wires yet.
- 3). Place a spark plug socket, with an extension and ratchet attached, over the spark plug and turn it counterclockwise to loosen it. Continue turning the plug until it is free from the cylinder head, then pull it out of the head.
- 4). Check the gap between the electrode and the base of the spark plug by sliding a feeler gauge into the gap. Compare the gap on the plug to the gap recommended by the vehicle manufacturer and adjust it as needed. If it is too tight, bend the electrode out a little. If it is too wide, tap the electrode in a little. The feeler gauge should pass through the gap with a slight drag when it is correct.
- 5). Install the new plug into the cylinder head and turn it clockwise by hand to get the threads started. This will help avoid crossthreading the spark plug. Tighten the spark plug with a socket and ratchet until snug then turn it about a quarter turn more.
- 6). Place a small amount of dielectric grease inside the spark plug boot and press the boot onto the plug. Push it down until you feel it click to make sure it is secure.
- 7). Move to the next plug and repeat the process, continuing around the engine until you have replaced all the spark plugs. Connect the negative battery cable to the negative post on the battery and tighten the retaining bolt with a wrench.
Source...