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.
| Fig. 1: A normally worn spark plug should have light
tan or gray deposits on the firing tip
|
| Fig. 2: 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
|
| Fig. 3: A variety of tools and gauges are needed for
spark plug service
|
| Fig. 4: A physically damaged spark plug may be evidence
of severe detonation in that cylinder. Watch that cylinder carefully between
services, as a continued detonation will not only damage the plug, but
could also damage the engine
|
| Fig. 5: Checking the spark plug gap with a feeler gauge
|
| Fig. 6: An oil fouled spark plug indicates an engine
with worn piston rings and/or bad valve seals allowing excessive oil to
enter the chamber
|
| Fig. 7: Adjusting the spark plug gap
|
| Fig. 8: 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
|
| Fig. 9: If the standard plug is in good condition, the
electrode may be filed flat — CAUTION: do not file platinum
plugs
|
| Fig. 10: 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
|
| Fig. 11: Used spark plugs which show damage may indicate
engine problems
|
