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The electrodes of a good spark plug are sort of tan in color, and the center electrode, if there is one, has a fairly sharp edge all the way around.
A bad spark plug can be black, or oily black, and the electrodes may be black-ish even down inside the ceramic where the center electrode comes out. The electrode edges may be worn down and rounded.
A bad spark plug will not have a continuous path from where the spark plug wire attaches to the center electrode. This can be checked with an ohm-meter.
If you're still not sure, it is best to replace spark plugs - they have a definite effect on power and gas mileage.
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∙ 12y ago
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How do you tell if a spark plug is bad?
If there is a question about it, replace it. They are not terribly expensive. If the plugs are starting to go bad, replace them all. And the spark plugs wires too. An ounce or prevention is worth a pound of cure.
What cause Ford expedition cylinder misfire?
Plugs or / and Coil Packs. Auto Zone will check your codes for free and will tell you which plugs or coils are bad. Then replace.
How would you know if the sparks plugs are bad or if the coil is bad on a 1999 ford expedition?
Auto Zone will check your codes for FREE... It will also tell you which one is bad.
What causes spark plugs to stop firing?
No spark from coil, bad plug wires, or bad plugs.
Will bad spark plugs cause an engine to burn oil?
No, but burning oil will give you bad spark plugs.
Can bad spark plugs cause your car to lose power and backfire in the intake manifold?
having bad spark plugs could effect how the spark sparks and when it sparks. new plugs is never a bad idea
How do you tell if your map sensor is bad on your 1996 4.3 Chevy v6?
It will be smoking black out of the exhaust / Running RICH. Spark plugs will be fouled out/ Black. Replace them if it is running rich. Plugs will not fix your problem. Replace map sensor.
Why does your truck go putt putt?
Bad gas. Or bad plugs
How can you tell if your head gaskets are bad?
Water in oil, steam from exhaust after engine has warmed up, compression test, pull spark plugs and look at electrodes.
Is it bad to change spark plugs early?
No.
Could bad spark plugs make a engine shake?
Bad engine cushions can make the engine shake. bad spark plugs cause malfunction as the car starts running.
Will a bad alternator cause new spark plugs to smoke?
Spark plugs don't smoke. A bad alternator would cause a dead battery.
