The Denali version of the GMC Yukon is a special edition on the high end of SUVs. High end does not mean that the vehicle doesn't need regular maintenance, however. In fact, while most manufacturers state that your spark plugs are good for 40,000 miles or more, you should never wait that long in between changing them. They do not cost that much, and the fresh plugs will keep your Yukon operating efficiently. It does not take that long to change them. If you have no experience working on an automobile, you can change all of the plugs in about an hour.
Disconnect the negative battery cable, loosening the nut with a wrench. Check the gap on the new spark plugs with a feeler gauge. The gap on the plugs should be .040. Insert the feeler gauge blade into the gap at the top of the plug. It should fit snugly. Plugs are factory set, but you need to check them anyway.
Pull one spark plug wire off the plug. Grasp the boot close to the engine and pull it off. Do not pull on the wire or you could break the filament inside. Remove the spark plug with a spark plug socket, ratchet and extension. Discard the old plug.
Put the new plug into the cylinder head and tighten it snugly. Be careful not to cross-thread the spark plug in the cylinder head or you will damage it. Place the spark plug wire onto the new plug and push it in until you feel it snap into place. Repeat the process on the next spark plug until you change them all.
