"K-town" <jdu52580@carolina.stopspam.rr.com> wrote in message news:<D6cqd.7794$Mu3.802926@twister.southeast.rr.c om>...
> Hello,
>
> Not being an engine expert, I figured I'd throw this question out to
> this NG. I have a 1990 Civic LX, 1.5L DPFI 5-speed, and usually I put
> regular unleaded (87 octane) in it. Every once in awhile I'll put mid-grade
> (89 octane) or premium (92 or 93 octane) in it because I heard that doing so
> will keep your injectors clean. (Is that true?) Once I really splurged and
> put 100 octane fuel in it (only 5 gallons) and it did run pretty good. One
> thing I noticed, is that if I run premium (93) in it several tanks in a row,
> it will actually not run quite as good. It's a very minuscule difference,
> but I can tell there is a slight decrease in performance. If I drop it back
> down to mid-grade or even back to regular on the next tank, it seems to go
> back to running better. Is this all in my head, or is it possible to have
> an "octane overkill" on such a small 4-cylinder engine?

Unless your engine is knocking, there is no need to spend the extra
money for a higher octane fuel. Use what the owner's manual recommends.

I suggest reading:
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
"The Low-Down on High Octane Gasoline"