Carbon in UIM?

[Cougar1146]

Can someone explain why I had so much Carbon build up in my UIM (Look at my previos post http://www.fastcougar.com/forums/messageview.cfm?catid=10&threadid=95674) I have used Quick Trip Gas 93 octane since I bought my car (New 1998) and used good Oil (Castrol 5w30). So what causes all the Carbon and what is the best gas?

Thanks.

[B3NN3TT]

93 octane is a COLOSSAL WASTE OF MONEY unless your compression is higher than stock, or unless you live in the Rocky Mountains. It has NO effect on carbon buildup, and only confuses your computer (since it's programmed for 87 octane).

Carbon builds up naturally in any engine. PCV recirculation blasts oil into the UIM as well.

Best gas is regular ol' 87 octane. It is a good idea, IMHO, to use a good fuel system cleaner every now and then. Techron is a good general use treatment. BG 44K is a MAD CRAZY twice-in-a-lifetime fuel system treatment that you might consider using now. Maybe like, every 50,000 miles or so.

[Cougar1146]

Well I have tried the 87 Octane (a long time ago) and it made the valves rattle like crazy, that is why I went to 93. So should I go back to 87?

Thanks.

[B3NN3TT]

That's because you HAD BEEN using 93. Making a drop in octane causes pinging (not rattling valves). It will do that for a tank or two, but once it figures out what you're giving it, it will be happier, and much better off. Not to mention the extra cash in your pocket...

Carbon on your piston heads and valve faces also cause pinging, especially with lower octane gas. A really good fuel system treatment and straight 87 octane will fix you up shortly.