I think, aside from combustion chamber carbon deposits, is the fact that high test premium gas is formulated to burn more slowly to prevent detonation in high compression engines. Regular gas burns faster and if all else is right with the engine and the emission numbers are ALMOST correct then using regular could possibly make the differance in passing emisssions. It's certainly a quick and easy thing to try and doesn't cost anything as compaired to throwing parts at your engine. Bruce Benson > --- In dmcnews@xxxxxxxxxxxxxxx, "Tom Niemczewski" <tomciodmc@xxxx> wrote: >> >> One of the reasons for your failed emissions might be the prolonged > use of >> premium fuel. I am assuming that you mean 93 octane. Higher octane gas >> causes deposits to form inside the cylinders and in the exhaust > system. That >> in turn will over time cause the compression to be raised. With that > you >> will get higher temperatures in the center of the cylinders along with >> unburned gasoline close to the edges of the cylinders. > > How come I've never heard of this? Granted, I'm not a mechanic nor an > engineer, but I'd think is this were true enough to cause problems > this knowledge would be more common than it is. To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/