walker11, octane rating is not going to affect the air/fuel mixture unless, of course the car is pinging, in which case the PCM will switch to a limp home mode (rich fuel, retard timing, trigger MIL) to save the engine from further damage.

What WILL cause the A/F mixture to run rich is if you mash your right foot to the floor on a regular basis. Under these conditions, the PCM switches from closed-loop to open-loop and will err on the side of rich-ness , again to save the engine from detonation. If this is your driving style, which I suspect it is, then you're going to have to live with a little soot on your exhaust tips. Alternatively, you could go to Home Depot and pick yourself up a can of Krylon flat-black barbeque paint and paint the inside of your tips black. That's what I did.

If you are concerned that the car is running rich all the time then I would suggest taking it to the dealer and expressing your concerns. They can plug in the DRB-III and see if the car is coughing-up any fault codes. Another indication would be your mileage. A Crossfire should get somewhere between 25 and 30 miles per gallon, depending on how it's driven.

Let us know what you find out...