Rodeo LS 4WD V6-3.2L (1998)
Spark Plug: Description and Operation
DESCRIPTION
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Although worn or dirty spark plugs may give satisfactory operation at idling speed, they frequently fail at higher engine speeds. Faulty spark plugs
may cause poor fuel economy, power loss, loss of speed, hard starting and generally poor engine performance. Follow the scheduled maintenance
service recommendations to ensure satisfactory spark plug performance.
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Normal spark plug operation will result in brown to grayish-tan deposits appearing on the insulator portion of the spark plug. 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." This means the ignition spark is not igniting the air/fuel mixture at the proper time. While other ignition and
fuel system causes must also be considered, possible causes include ignition system conditions which allow the spark voltage to reach ground in
some other manner than by jumping across the air gap at the tip of the spark plug, leaving the air/fuel mixture unburned. Refer to DTC P0300.
Misfiring may also occur when the tip of the spark plug becomes overheated and ignites the mixture before the spark jumps. This is referred to as
"pre-ignition."
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Spark plugs may also misfire due to fouling, excessive gap, or a cracked or broken insulator. If misfiring occurs before the recommended
replacement interval, locate and correct the cause.
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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
and slow speeds under light engine loads can keep the spark plug temperatures so low that these deposits are not burned off. Very rich fuel
mixtures or poor ignition system output may also be the cause. Refer to DTC P0172.
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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 during break-in of new or newly overhauled engines. Deposit fouling of the spark plug occurs when the normal
red-brown, yellow or white deposits of combustion by-products become sufficient to cause misfiring. In some cases, these deposits may melt and
form a shiny glaze on the insulator around the center electrode. It the fouling is found in only one or two cylinders, valve stem clearances or intake
valve seals may be allowing excess lubricating oil to enter the cylinder, particularly if the deposits are heavier on the side of the spark plug facing
the intake valve.
