Spark Plug Visual Inspection
- Normal Operation
- Brown to Grayish-Tan with small amounts of White powdery deposits are normal combustion by-products from fuels with additives.
- Carbon Fouled
- Dry, fluffy Black carbon, or soot caused by rich fuel mixtures, leaking fuel injectors, excessive fuel pressure, restricted air filter element or incorrect combustion. Reduced ignition system voltage output, weak coils worn ignition wires or incorrect spark plug gap. Excessive idling or slow speeds under light loads can keep spark plug temperatures so low that normal combustion deposits may not burn off.
- Deposit Fouling
- Oil, coolant, or additives that include substances such as silicone, very white coating, reduces the spark intensity. Most powdery deposits will not effect spark intensity unless they form into a glazing over the electrode.
Courtesy of GENERAL MOTORS CORP.