Seville STS V8-4.6L VIN 9 (1998)
Spark Plug: Testing and Inspection
Follow the Scheduled Maintenance Services to assure satisfactory spark plug performance. Normal spark plug operation will result in brown to
grayish-tan deposits appearing on the portion of the spark plug that projects into the cylinder area. A small amount of red-brown, yellow, and white
powdery material may also be present on the insulator tip around the center electrode. These deposits are normal combustion by-products of fuels and
lubricating oils with additives. Some electrode wear will also occur.
Engines which are not running properly are often referred to as misfiring. For information on misfiring, Refer to Cuts Out, Misses in Computers and
Control Systems.
Flashover occurs when a damaged spark plug boot, along with dirt and moisture, permits the high voltage charge to short over the insulator to the spark
plug shell or the engine. Should misfiring occur before the recommended replacement interval, locate and correct the cause.
Carbon fouling of the spark plug is indicated by dry, black carbon (soot) deposits on the portion of the spark plug in the cylinder Excessive idling or
slow speeds under light engine loads can keep the spark plug temperatures so low that these deposits are not burned off. Rich fuel mixtures or poor
ignition system output may also be the cause; Refer to Rough, Unstable, or Incorrect Idle and Stalling in Computers and Control Systems.
Oil fouling of the spark plug is indicated by wet oily deposits on the portion of the spark plug in the cylinder, usually with little electrode wear. This may
be caused by oil getting past worn piston rings or valve seals. This condition also may occur during break-in of new or newly overhauled engines.
