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?

Thanx in advance,

Jonathan