With the Land Rover Spark Plugs in place and igniting the air and fuel mixture, the engine can operate as it was designed too. The spark plugs are the action component of the ignition system on your Land Rover.
The number of cylinders in the engine of your Land Rover determines the number of spark plugs being used by it. An eight cylinder motor has eight and a six cylinder engine has six. Each of the Land Rover spark plugs must be in proper working condition for the engine to operate at it maximum power potential and run smoothly. If just one of the spark plugs is misfiring or is fouled out, the engine will run rough and vibrate more than usual.
There are two methods in determining which of the plugs is misfiring. By removing one spark plug wire at a time when the engine is operating, the one that is misfiring or fouled out can be pulled without it negatively affecting the way the engine is running.
The second method of determine the health of a plug is by pulling them from the engine. If the plug has been firing correctly the two points in the gap that create the arc will be clean. The ceramic near the end of it will also be white to slightly dark. If it is tan then the air to fuel ratio of the engine is lean. When the plug is pulled and the end is covered with black soot, the air and fuel ratio is too rich. When there is residue in the gap, then the spark plug is fouled out. It can either be cleaned or replaced when found in this condition.