Ford Mustang (1999-2004) Service Manual: Spark Plug

Removal

1. Remove the ignition coil on plug. For additional information, refer to Ignition Coil-Coil On Plug in this section.

2. NOTE: Use compressed air to remove any foreign material from the spark plug well before removing the spark plugs (12405).

NOTE: If an original spark plug is used, make sure it is installed in the same cylinder from which it was taken. New spark plugs can used in any cylinder.

NOTE: One spark plug is shown; others are similar.

Remove the spark plugs

Spark Plug

3. Inspect for gap bridged.

  • This can be identified by a deposit build up closing the gap between electrodes.
  • This can be caused by oil or carbon fouling.
  • Clean the spark plug.

Spark Plug

4. Inspect for oil fouling.

  • This can be identified by wet black deposits on the insulator shell bore electrodes.
  • This can be caused by excessive oil entering the combustion chamber through worn rings and pistons, excessive clearance between valve guides and stems, or worn or loose bearings. Correct the oil problem.
  • Install a new spark plug.

Spark Plug

5. Inspect for carbon fouling.

  • This can be identified by black, dry fluffy carbon deposits on insulator tips, exposed shell surfaces and electrodes.
  • This may be caused by too cold a plug, dirty air cleaner, damaged fuel pump, too rich a fuel mixture or excessive idling.
  • Clean the spark plug.

Spark Plug

6. Inspect for normal burning.

  • This can be identified by light tan or gray deposits on the firing tip.

Spark Plug

7. Inspect for pre-ignition.

  • This can be identified by melted electrodes and possibly a blistered insulator. Metallic deposits on insulator indicate engine damage.
  • Install a new spark plug.

Spark Plug

8. Inspect for overheating.

  • This can be identified by a white or light gray insulator with small black or gray brown spots and with bluish-burnt appearance of the electrodes.
  • This may be caused by engine overheating, wrong type of fuel, loose spark plugs, too hot a plug, low fuel pump pressure or incorrect ignition timing.
  • Install a new spark plug.

Spark Plug

9. Inspect for fused spot deposits.

  • This can be identified by melted or spotty deposits resembling bubbles or blisters.
  • This may be caused by sudden acceleration.
  • Clean the spark plug.

Spark Plug

Installation

1. Adjust the spark plug gap as necessary.

Spark Plug

2. To install, reverse the removal procedure.

Spark Plug

 

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