Reading Your Spark Plugs
Much can be learned about your engine's condition by reading your spark plugs.
Below are some explanations on cause and affect of what you might see when viewing your spark plugs.
Grayish-tan to white in color indicates the plug is in the proper heat range as well as having the correct air fuel mixture.
Worn Out Plugs
Excessive electrode wear, misfire during acceleration and hard to start.
The plug is just worn out. Looks are ok color wise, replace with the same plug and heat range.
This is caused by foreign objects in the cylinder or maybe a plug with an improper reach that can contact the piston.
The fix is to, make sure you have the correct length spark plug.
Where you have severe detonation, insulators may become chipped or cracked. An improper spark plug gap settings will sometimes also cause the insulator tip to chip.
Check to see if you are using the correct octane fuel and then verify ignition timing. Next you can check for an bad EGR system and for the proper function of the Knock Sensor (not all cars have them). Also, you will want to make sure you are using the correct heat range plug.
Plug has a chalky appearance, white insulator, electrode wear as well as very few deposits.
You will probably need to go to a colder plug.
These are light brownish deposits that are covering the ground or the center electrode. This is caused by your oil or maybe the fuel additives. This condition can cause misfires.
Check for worn valve guides or maybe the valve seals, or try using a different fuel brand.
Oily black coating caused by a worn oil control system. Oil is leaking past worn valve guides or piston rings.
This will usually look like a melted center electrode or a ground electrode.
Check for an
Incorrect heat range plug, Bad knock Sensor, Inoperative EGR valve, Timing too far advanced, A lean fuel mixture
Sustained Pre ignition:
Melted or missing center ground electrodes as well as maybe a damaged insulator.
Check for incorrect heat range of the plug, over advanced timing, a lean fuel mixture, an inoperative EGR valve or a bad Knock Sensor.
These are small spots of deposits on the insulator. This could be a dirty carburetor or maybe an air intake or dirty injectors.
Soft, black, sooty, dried looking carbon.
This indicates a rich mixture a weak ignition or maybe a too cold of a heat range.