Quote Originally Posted by GM_TUNER
I know that when an engine is running ~perfect air-fuel ratio, the spark plugs tend to look like a brownish, coffee-color or a greyish-tan color, but what does it mean when the spark plugs are just GREY. Not white, just grey...

I know that white spark plugs mean the engine is running too lean, and black/sooty ones mean the engine is running too rich, but im not sure about grey... I can post pics if anyone needs to see what im talking about
For driveability tuning, you can't read spark plugs due to the fact that the only accurate reading will be from a wot shut off, under a load. The only way you can take advantage of reading plugs, is if you have a power adder, and make wot pulls so you can see where the timing needs to be and what the fuel is doing.