ION, L-Series, S-Series 1999-2005

Spark Plugs 1

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A typical spark plug consists of a metal shell surrounding a ceramic insulator. A metal electrode extends downward through the center of the insulator and protrudes a small distance. Located at the end of the plug and attached to the side of the outer metal shell is the side electrode. The side electrode bends in at a 90( angle so that its tip is just past and parallel to the tip of the center electrode. The distance between these two electrodes (measured in thousandths of an inch or hundredths of a millimeter) is called the spark plug gap.

The spark plug does not produce a spark, but instead provides a gap across which the current can arc. The coil produces anywhere from 20,000 to 50,000 volts (depending on the type and application) which travels through the wires to the spark plugs. The current passes along the center electrode and jumps the gap to the side electrode, and in doing so, ignites the air/fuel mixture in the combustion chamber.

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Fig. Cross-section of a spark plug

A typical spark plug consists of a metal shell surrounding a ceramic insulator. A metal electrode extends downward through the center of the insulator and protrudes a small distance. Located at the end of the plug and attached to the side of the outer metal shell is the side electrode. The side electrode bends in at a 90( angle so that its tip is just past and parallel to the tip of the center electrode. The distance between these two electrodes (measured in thousandths of an inch or hundredths of a millimeter) is called the spark plug gap.

The spark plug does not produce a spark, but instead provides a gap across which the current can arc. The coil produces anywhere from 20,000 to 50,000 volts (depending on the type and application) which travels through the wires to the spark plugs. The current passes along the center electrode and jumps the gap to the side electrode, and in doing so, ignites the air/fuel mixture in the combustion chamber.

Click image to see an enlarged view

Fig. Cross-section of a spark plug

Inspection & Gapping



Check the plugs for deposits and wear. If they are not going to be replaced, clean the plugs thoroughly. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug cleaning machine, which can sometimes be found in service stations, or you can do an acceptable job of cleaning with a stiff brush. If the plugs are cleaned, the electrodes must be filed flat. Use an ignition points file, not an emery board or the like, which will leave deposits. The electrodes must be filed perfectly flat with sharp edges; rounded edges reduce the spark plug voltage by as much as 50%.

Check spark plug gap before installation. The ground electrode (the L-shaped one connected to the body of the plug) must be parallel to the center electrode and the specified size wire gauge (please refer to the Tune-Up Specifications chart for details) must pass between the electrodes with a slight drag.


NOTE
NEVER adjust the gap on a used platinum type spark plug.

Always check the gap on new plugs, as they are not always set correctly at the factory. Do not use a flat feeler gauge when measuring the gap on a used plug, because the reading may be inaccurate. A round-wire type gapping tool is the best way to check the gap. The correct gauge should pass through the electrode gap with a slight drag. If you're in doubt, try one size smaller and one larger. The smaller gauge should go through easily, while the larger one shouldn't go through at all. Wire gapping tools usually have a bending tool attached. Use that to adjust the side electrode until the proper distance is obtained. Absolutely NEVER attempt to bend the center electrode. Also, be careful not to bend the side electrode too far or too often, as it may weaken and break off within the engine, requiring removal of the cylinder head to retrieve it.

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Fig. A normally worn spark plug should have light tan or gray deposits on the firing tip



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Fig. A carbon fouled plug, identified by soft, sooty, black deposits, may indicate an improperly tuned vehicle. Check the air cleaner, ignition components and engine control system



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Fig. A variety of tools and gauges are needed for spark plug service



Click image to see an enlarged view

Fig. A physically damaged spark plug may be evidence of severe detonation in that cylinder. Watch that cylinder carefully between services, as continued detonation will not only damage the plug, but could also damage the engine



Click image to see an enlarged view

Fig. Checking the spark plug gap with a feeler gauge



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Fig. An oil fouled spark plug indicates an engine with worn piston rings and/or bad valve seals, allowing excessive oil to enter the chamber



Click image to see an enlarged view

Fig. Adjusting the spark plug gap



Click image to see an enlarged view

Fig. This spark plug has been left in the engine too long, as evidenced by the extreme gap. Plugs with such an extreme gap can cause misfiring and stumbling, accompanied by a noticeable lack of power



Click image to see an enlarged view

Fig. If the standard plug is in good condition, the electrode may be filed flat-WARNING: do not file platinum plugs



Click image to see an enlarged view

Fig. A bridged or almost bridged spark plug, identified by a build-up between the electrodes, caused by excessive carbon or oil build-up on the plug



Click image to see an enlarged view

Fig. Used spark plugs which show damage may indicate engine problems

Check the plugs for deposits and wear. If they are not going to be replaced, clean the plugs thoroughly. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug cleaning machine, which can sometimes be found in service stations, or you can do an acceptable job of cleaning with a stiff brush. If the plugs are cleaned, the electrodes must be filed flat. Use an ignition points file, not an emery board or the like, which will leave deposits. The electrodes must be filed perfectly flat with sharp edges; rounded edges reduce the spark plug voltage by as much as 50%.

Check spark plug gap before installation. The ground electrode (the L-shaped one connected to the body of the plug) must be parallel to the center electrode and the specified size wire gauge (please refer to the Tune-Up Specifications chart for details) must pass between the electrodes with a slight drag.


NOTE
NEVER adjust the gap on a used platinum type spark plug.

Always check the gap on new plugs, as they are not always set correctly at the factory. Do not use a flat feeler gauge when measuring the gap on a used plug, because the reading may be inaccurate. A round-wire type gapping tool is the best way to check the gap. The correct gauge should pass through the electrode gap with a slight drag. If you're in doubt, try one size smaller and one larger. The smaller gauge should go through easily, while the larger one shouldn't go through at all. Wire gapping tools usually have a bending tool attached. Use that to adjust the side electrode until the proper distance is obtained. Absolutely NEVER attempt to bend the center electrode. Also, be careful not to bend the side electrode too far or too often, as it may weaken and break off within the engine, requiring removal of the cylinder head to retrieve it.

Click image to see an enlarged view

Fig. A normally worn spark plug should have light tan or gray deposits on the firing tip



Click image to see an enlarged view

Fig. A carbon fouled plug, identified by soft, sooty, black deposits, may indicate an improperly tuned vehicle. Check the air cleaner, ignition components and engine control system



Click image to see an enlarged view

Fig. A variety of tools and gauges are needed for spark plug service



Click image to see an enlarged view

Fig. A physically damaged spark plug may be evidence of severe detonation in that cylinder. Watch that cylinder carefully between services, as continued detonation will not only damage the plug, but could also damage the engine



Click image to see an enlarged view

Fig. Checking the spark plug gap with a feeler gauge



Click image to see an enlarged view

Fig. An oil fouled spark plug indicates an engine with worn piston rings and/or bad valve seals, allowing excessive oil to enter the chamber



Click image to see an enlarged view

Fig. Adjusting the spark plug gap



Click image to see an enlarged view

Fig. This spark plug has been left in the engine too long, as evidenced by the extreme gap. Plugs with such an extreme gap can cause misfiring and stumbling, accompanied by a noticeable lack of power



Click image to see an enlarged view

Fig. If the standard plug is in good condition, the electrode may be filed flat-WARNING: do not file platinum plugs



Click image to see an enlarged view

Fig. A bridged or almost bridged spark plug, identified by a build-up between the electrodes, caused by excessive carbon or oil build-up on the plug



Click image to see an enlarged view

Fig. Used spark plugs which show damage may indicate engine problems

 
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