Spark Plugs: Inspection

Reconnect negative battery cable.
Connect spark plug to high-tension lead.
Hold spark plug with insulated pliers 0.2 to 0.39 inch (5~10 mm) from a ground.
WARNING: Do not touch vehicle body during following instructions.
While holding spark plug, have a second person crank engine. Verify that a strong blue spark jumps from spark plug to ground.

Fig 1: Testing For Proper Spark
Courtesy of KIA MOTORS AMERICA, INC.
If there is no spark or the spark is weak, check for, and implement correction:
- Carbon deposits. Clean out or replace plug.
- Oil fouling. Correct oil problem, replace plug.
- Worn or burnt electrode. If present, replace plug.
- Broken or burned ceramic insulator. If present replace plug.
- Damaged spark plug ring. If so, replace ring.
- Improper spark plug gap. Regap if possible, otherwise replace plug.
Gap: 0.027~0.031 inch (0.7~0.8 mm)

Fig 2: Inspecting Spark Plug Condition
Courtesy of KIA MOTORS AMERICA, INC.