Spark Plug: Testing and Inspection

Checking Spark Plug For Wear, Damage, Or Deposits:

1. Remove spark plug wire and spark plug.

Visual Spark Plug Inspection:

2. Inspect the spark plug for:
a. Improper gap
b. Carbon deposits
c. Cracked center electrode insulator
d. Burned or worn electrodes (may be caused by):
Excessive mileage
Lean fuel mixture
Advanced ignition timing
Loose spark plug
Plug heat range too high
Insufficient Cooling
e. Fouled plug (may be caused by):
Rich fuel mixture
Retarded ignition timing
Oil in combustion chamber
Incorrect spark plug gap
Plug heat range too low
Excessive idling/low speed running
Clogged air cleaner element
Deteriorated ignition coil, coil wire or ignition wires
3. Replace the plug if the center electrode is rounded (except some platinum type plugs which have a very small diameter center electrode with an insulator that covers the electrode to the tip and may be rounded), this indicates high milage.
4. Adjust the gap with a suitable gapping tool to the following specification:

0.027 - 0.035 in. (0.7 - 0.9 mm)

5. Reinstall spark plug. Use some anti-seize compound on the threads and torque to:

15 ft.lbs (20 Nm)

6. Reconnect spark plug wire.