Question about 1987 Toyota 4Runner

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Got carbon buid up on spark plugs

What is the deal with carbon on the spark plugs

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  • yadayada
    yadayada May 11, 2010

    how are the tail pipe levels of CO and HC? does it use more than 1 quart of oil in 500 miles? How is the MPG? How many miles on the engine?



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Carbon build up comes from too much oil going into the cylinder and not being burned off. leak from a valve guide or oil bypassing the rings. is it on just one or all the plugs?

Posted on Mar 14, 2009


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What additives can be use to clean piston head with valve

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The porcelain spark plugs keep on cracking when the car is being used

Is the porcelain "cracking" or are they getting "carbon-tracked"? (see example photo of carbon-tracked plug below).
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Do a test for spark at the plugs. Remove one of the plug wires from a plug and hold it near grounded metal. (If the plug end has a long insulated shroud, you may have to improvise to get ground close enough to the end of the wire.) Have someone crank the engine while you watch for spark. If you get an 1/8" or so of spark, that should be enough to fire.Check the distributor cap inside for signs of cracks or carbon arc tracks.Also, check to see that the little carbon contact for the center terminal is in place; without that you can have spark but it won't get to any plug wires.It's rare, but a rotor with an internal short or carbon tracks on the surface can kill the spark before it even gets to the cap.

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Carbon build up comes from rich mixture or weak ignition. This will cause misfiring, hesitation and hard starting. To fix the problem, change the plugs and use a plug that will produce a higher heat range. Which means it has a hotter firing/ignition when combustion. This will burn the excess gas that causes the carbon. Be sure to check the plug wires to make sure you don't have spark jumping. (check at night with engine running). Also be sure the air filter is clean.

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Dead olds

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it sounds right, it is called a light load miss. it occurs mostly at 45-50 mph on slight incline and it feels like a bucking or hesitation. It commonly ocurs when there is carbon tracking on a spark plug porcelin (sp) . note . if the porcelin has carbon tracking so does the plug wire boot. the spark will travel through the carbon track in teh boot after plug replacement causing premature failure of the plug. it is a good idea to replace plugs and wires if this is the cause of your miss.

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