I just brought a 2000 seville SLS, 4.6L, " Y" engine code w/ 69k mi. (8/07). My first question is your opinion of Synthetic oils. My car has 73K mi and I put Royal Purple, 5w-30 Synthetic oil & Lucas Synthetic oil additive and installed an K& N Air filter. Was this a wise decision? My second question is, Isn't it a sign that a carbon coating in the tailpipe a sign of a engine running lean. If it is what can I do to fix this? Should I tune it up before 100K mark? I don't no what kind of care or maintance was done before I brought it. I'm planning on installinstalling Denso's Iridium spark plugs after the holidays. Any thougths? It took me a half a tank of gas ($40) to travel 180 mi (upstate PA, other side of the Pocono mountains), is this suppose to happen? YIKES!
Black soot in tail pipe is a darivative of premium gas, you need to open her up and blow it out, put ac plugs in, your asking for trouble, also run injector cleaner through it to help with carbon( every couple weeks)