Reading spark plugs

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The spark plug is a window into the combustion chamber. To a well trained eye, the plug can tell a volume of information about the engine's condition, air/fuel mixture, timing, fuel distribution through the intake tract, and more.
 
The spark plug is a window into the combustion chamber. To a well trained eye, the plug can tell a volume of information about the engine's condition, air/fuel mixture, timing, fuel distribution through the intake tract, and more.
  
No single article will be able to bring someone from a beginner to a pro at anything, and reading plugs is no exception. But the basics can be conveyed well enough to get a leg up on how to read a plug.
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No single article will be able to bring someone from a beginner to a pro at anything, and reading plugs is no exception. But the basics can be conveyed well enough to get a leg up on how to read a plug beyond the common practice of looking at a plug with thousands of miles, as well as recent stop and go driving on it, to tell what is going on inside the engine.
  
The following article draws heavily on an article written by Brian Odom. It has been reprinted many times on the internet because it's as complete as any article on the subject, as well as including good photography to supplement the text.  
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While that can give a general idea of conditions on a very broad scale, there are more precise ways of reading a plug.
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The following article draws heavily on an article written by Brian Odom. It's as complete, if not more, so than most articles on the subject as well as including photographs to supplement the text.
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[[File:FLASHLIT.jpg|right]]
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==Magnifier==
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It's imperative that a light source with a magnifier be used to read plugs, because the plug insulator at the deepest point is one of the things that is looked at. If the light source isn't uniform from reading to reading, the slight coloring differences can be misread. The idea is to have repeatable conditions.
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Many plug magnifier/lights use 10X magnification. The choice then becomes LED or incandescent light bulb(s). If possible try both to see which is preferred.
  
 
==Tuning an engine by reading the spark plug==
 
==Tuning an engine by reading the spark plug==

Revision as of 11:49, 17 January 2013

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