Thread: Reading Spark Plugs

Over at cow town we're discussion different tuning tips. I though I'd post some of them up here for you guys, maybe you'll learn something new, maybe it's well known :) Either way, here's a little bit on reading plugs.

Reading plugs involves looking at the porcelain insulator of the center electrode and the general condition of the center electrode and ground electrode. It's best to use a lighted magnifying glass and inspect the plugs directly after a dyno pull. Leaving the car running or driving afterwards can change the condition of the plug and tell you nothing. Biggest thing you can look for is signs of detonation. It will look like dark gray or silver specs of pepper sprinkled on the white insulator. This is aluminum being vaporized of your pistons or combustion chamber from the high heat and pressure spike of detonation. Other signs of knock are small balls that look like weld splatter on the center and ground electrode that can be seen under a magnifying glass or a yellowish to blue-greenish color.

You can also tell if you're running too lean or rich. Old timers will tell you to shoot for a chocolate brown color but this is only true on fuel with large amounts of lead. On today?s unleaded pump fuel, it will range from a bone white to light brown. Race fuel will range from light tan to medium brown. Too lean and the plug will have a bleach white flaky look, too rich and it will be dark brown or black and have that sooty look and feel to it. If something?s seriously wrong with your fuel delivery system like an injector stuck open, the plug could be wet and black and would smell like gas. An engine that's burning oil will have a sticky black carbon coating.

is it bad if the electrode is burned off??