The detergents in gasoline are designed to keep your fuel system clean, so if you use a lower quality fuel or use a lower octane fuel (when your car requires premium) regularly, then it may be a good idea to use some fuel system cleaner every once in awhile. For example, my Integra has a very high compression ratio (10:1) and the manual says I should only use Premium unleaded, well I was cheap and used regular for about 6 months (my engine was knocking like crazy) when I switched back to premium my engine would still knock, I used some fuel system cleaner and the knock dissapeared.

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Adam,
1986 300E
1997 Acura Integra GS-R