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.