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Discussion Starter #1
Someone once said that you can tell if the car is running lean or rich by looking at the sparkplugs when they are being changed.

How DO you tell. What do I look for to see if my car is running lean or rich?

Insang
 

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Retired Super-Mod
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10,170 Posts
If it's rich the plug tip will be black and sooty.

If it's lean the plug tip will be white...

Any Haynes manual has this information.
 

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Old School
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4,014 Posts
The only way to really do this is:

1. Install new plugs.

2. Make a 1/4 mile pass (or similar load on motor).

3. Shut car down ASAP at the end of the 1/4, no idling, and pull the plug(s).

There will be a thin band high up on the insulator, the color and position can tell you a lot about A/F. Tan is good, the higher up the better.

You can try and find a copy of "The Doctors Step by Step Guide to Optimizing Your Ignition" by Dr. Christopher Jacobs. It has lots of great, generic info. I have a copy, but I'm not selling. :)

When you check plugs that have been in the motor for thousands of miles you are evaluating the overall condition of the motor.
 
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