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Here are a couple pics of the plugs I just pulled out of my car. My WB reads very lean but according to the www.mkiv.com website, the plugs indicate I'm running rich. Am I reading them right?
Just in case you can't tell from the pictures, they are a white/greenish yellow color. I guess the term used at www.mkiv.com "sooty" could be used to describe the texture too.
 
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Pictures are too poor to tell much.

If you have a greenish hue to 'em, that's probably due to high octane race gas.

I'd say a tan to brown is what you'd like, and definitely no fly-turds on 'em (very small flecks of metal, which is due to detonation damage).

You also have to remember that if you are driving on plugs for miles and miles... some WOT blasts *may* not discolor them to where you can read them for performance readings.
 

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I always thought tan to brown meant lean, where as black means you are running rich. I don't know what a yellowish green means, but tan to brown means lean & black means rich.
 
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I've never seen tan to brown considered as lean. This is all relative anyways. You are tuning the motor to run 'rich' at WOT, how rich is the issue, if you are doing tuning for performance/safety. Every simple/generic guide shows tan/brown as normal running. Black & sooty is rich, or too cold a plug. White, clean plugs means it's running lean, or has too hot a plug.

Reading plugs is a science, most any plug reading you do with the naked eye is going to be guesstimation and only really tell you of very apparent problems rather than being very useful for tuning.

Use Google to find some really detailed information on this subject.

One thing I am sure to do, is to make sure that your plugs are consistent from cylinder to cylinder.
 

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Those look to be lean to me. I can't tell 100% but it looks like the porceline is pretty close to white. The porceline should be like a dark coffee color(i.e. lots of coffee with just a little cream) The only way to test this for sure is rough on the turbo. Make a 1st gear to top of 2nd. gear pull and then kill the car and coast to the side of the road. Pull plugs and then they will tell the tale. Any idleling done after the WOT pass severly alters the reading of the plugs. If the have the right color make another pull from first to 3rd. gear and pull plugs again. Also you must inspect the leanest cylinder to be safe. My cars leanest as most other supras is number 6. Good luck, Drew
 

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65vette396 said:
Any idleling done after the WOT pass severly alters the reading of the plugs. If the have the right color make another pull from first to 3rd. gear and pull plugs again. Also you must inspect the leanest cylinder to be safe. My cars leanest as most other supras is number 6.
very good point. cars are generally tuned to idle lean as hell, so if you go out and make a few blasts you may get back and think you are running lean. i would either judge by what the wideband tells you or do what he's said... you'd have to pull them immediately.
 
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