Hmm, my spark plugs are all black

Messages
1,983
Location
New Brunswick
Took out my spark plugs a few days ago just for the heck of it. I noticed 3 of the 4 were slightly blackened. On a few occasions the car has puffed out blue clouds of smoke, but usually only for a few seconds at a time. I have noticed that my gas mileage is a bit lower now than when I bought the car in September, but I just assumed this is because of the winter gas now being pumped at gas stations. I also use MMO frequently, and usually at slightly higher than normal dosage rates. My tank is 17 gallons, and when I fill it up I usually put 8 ounces or so in the tank. I know I'm supposed to use only 4 ounces per 10 gallons, but I find it's a lot easier to pour 8 ounces than to figure out how many ounces for how many gallons. Would my slightly higher than normal dosages of MMO cause my plugs to get that dirty black color? Oh, also I think my air filter is dirty. Not completely filthy mind you, but it is due to be replaced.
 
Messages
4,646
Location
The Garden State
Let's see, your plug center insulators are carbon dry black, and your gas mileage is down. It sounds like you have a rich running condition. Unless you've been running recently short trips where the engine, not just the coolant, never gets up to operating temps. Whimsey
 
Messages
333
Location
Shreveport, LA, USA
What kind of car??? Yes, it sounds like good ol' rich running to me, as well. I know on my saabs, the ECU will dump some extra fuel at high boost in order to prevent detonation.
 
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