GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Caprice WM 🢒 Engine 🢒 Engine Controls and Fuel - 6.0L 🢒 Spark Plug Inspection

Spark Plug Usage
    • Make sure that the correct spark plug is installed. An incorrect spark plug causes poor driveability conditions. Refer to Ignition System Specifications .
    • Make sure that the spark plug has the correct heat range. An incorrect heat range causes the following conditions:
       - Spark plug fouling due to a colder plug
       - A pre-ignition condition, causing spark plug and/or engine damage due to a hotter plug

Spark Plug Inspection
   • 
Object Number: 1950748 Size: SH
  • Inspect the terminal post (1) for damage.
    •    - Inspect for a bent or broken terminal post (1).
       - Test for a loose terminal post (1) by twisting and pulling the post. The terminal post (1) should NOT move.
       • 
    Object Number: 1950748 Size: SH
  • Inspect the insulator (2) for flashover or for carbon tracking soot. This condition is caused by the electrical charge travelling across the insulator (2) between the terminal post (1) and ground. Inspect for the following conditions:
    •    - Inspect the spark plug boot for damage.
       - Inspect the spark plug recess area of the cylinder head for moisture from such as oil, coolant, or from water. A saturated spark plug boot causes arcing to ground.
       • 
    Object Number: 1950748 Size: SH
  • Inspect the insulator (2) for cracks. All or part of the electrical charge may arc through the crack instead of through the electrodes (3, 4).
    •    • 
    Object Number: 1950748 Size: SH
  • Inspect for evidence of incorrect arcing.
    •    - Measure the gap between the centre electrode (4) and the side electrode (3) terminals. Refer to Ignition System Specifications .
       - Inspect for the correct spark plug torque. Refer to Ignition System Specifications . Insufficient torque can prevent correct spark plug operation. An over-torqued spark plug causes the insulator (2) to crack.
       - Inspect for signs of tracking that occurred near the insulator tip instead of at the centre electrode (4).
       - Inspect for a side electrode (3) that is broken or worn.
       - Inspect for a broken, worn, or loose centre electrode (4) by shaking the spark plug.
       • A rattling sound indicates internal damage.
       • A loose centre electrode (4) reduces the spark intensity.
       - Inspect for bridged electrodes (3 and 4). Deposits on the electrodes reduce or eliminate the gap.
       - Inspect for worn or missing platinum pads on the electrodes (3 and 4), if equipped.
       - Inspect for excessive fouling.
       • 
  • Inspect the spark plug recess area of the cylinder head for debris. Dirty or damaged threads can cause the spark plug not to seat correctly during installation.

    • Spark Plug Visual Inspection
       • 
  • Normal operation. Brown to grayish-tan spark plugs, with small amounts of white powdery deposits are normal combustion by-products from fuels with additives.
    •    • 
  • Carbon-fouled plugs. Dry, fluffy black carbon or soot caused by the following conditions:
    •    - Rich fuel mixtures
       • Leaking fuel injectors
       • Excessive fuel pressure
       • Restricted air filter element
       • Incorrect combustion
       - Reduced ignition system voltage output
       • Weak coils
       • Worn ignition wires
       • Incorrect spark plug gap
       - Excessive idling or slow speeds during light loads can keep the spark plug temperatures so low that the normal combustion deposits may not burn off.
        • Deposit fouling. Oil, coolant, or additives that include substances such as silicone, evidenced by a very white coating, reduces the spark intensity. Most powdery deposits will not affect spark intensity unless they form into a glazing over the electrode.