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Chapter 13 Preventive Maintenance and Troubleshooting
Spark Plug Service
The spark plug should periodically be removed
for inspection and cleaned or replaced. Begin by
using compressed air to blow dirt away from the
base of the spark plug. Remove the spark plug wire
from the plug by pulling on the wire’s insulating boot
only. Do not pull on the wire itself. See Figure 13-10.
Install a deep spark plug socket on the plug
and carefully turn the ratchet handle counter-
clockwise. Unscrew the spark plug and remove it
from the cylinder head.
Carefully examine the electrode end of the
plug. The electrodes and ceramic insulator should
be dry. An insulator or electrodes that are wet with
fuel or oil may be a sign of serious engine prob-
lems. A dry insulator that has a beige or gray/tan
color indicates that the engine is in good condition.
Next, examine the electrodes for any erosion, burn-
ing, or carbon fouling. Refer to Spark Plug Condition
chart in the Appendix of this text.
If the spark plug insulator and electrodes
appear to be good (no evidence of fouling or
wear), the plug can be reinstalled. If not, install a
new plug of the correct type. Refer to the manu-
facturer’s technical service manuals for the proper
replacement spark plug.
Check the electrode gap with a wire-type feeler
gauge, Figure 13-11. The engine service manual
will specify the proper gap setting. If the gap is too
large, carefully bend the outer electrode toward the
center electrode until the gap is correct. Use the gap
setting tool.
Before installing the spark plug, clean the
external ceramic insulator by wiping it with a clean
cloth. Condensation can cause fl ashover (sparking
externally) and erratic running if the insulator has
a coating of dirt on it. If the metal base is rusty,
Figure 13-9.
Lubricant can be sprayed between the cable and the
housing.
Cable Housing
Spray lubricant
Figure 13-10.
When removing a spark plug wire from the plug, pull
on the boot only. Do not pull on the wire itself.
Spark plug
Boot
Figure 13-11.
A wire-type feeler gauge is being used to check spark
plug gap.
Wire-type
feeler gauge