Spark Plug: Testing and Inspection

Checking Spark Plug For Wear, Damage, Or Deposits:

1. Inspect spark plugs for:

a. Incorrect gap.
b. Carbon deposits.
c. Cracked center electrode insulator.
d. Burned or worn electrodes.
e. Fouling.

2. Burned or worn electrodes may result from:

a. Excessive mileage.
b. Lean fuel mixture.
c. Advanced ignition timing.
d. Loose plug.
e. Plug heat range too high.
f. Insufficient engine cooling.

3. Plug fouling may result from:

a. Rich fuel mixture.
b. Retarded ignition timing.
c. Excessive oil consumption.
d. Incorrect plug gap.
e. Plug heat range too low.
f. Excessive idling / low speed running.
g. Clogged air filter element.
h. Faulty coil or ignition wires.

4. Platinum type plugs may have a small diameter center electrode surrounded by the insulator. It is normal for the electrode and insulator tip to have a rounded appearance that would indicate excessive wear in standard plugs.
5. When replacing plugs, adjust gap to 0.039 - 0.043 in (1.0 - 1.1 mm) and torque to 11 - 17 ftlb (15 - 23 Nm).