Miata Mailing List: September 1992, Message #75
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   From: (none)
Subject: re: better gas . . .
   Date: (none)

Following the owner's manual advice, I dutifully put regular gas in
my miata the first time I filled it up after the dealer's gas ran
out.  It knocked under hard second and third gear acceleration.  Not
a bad nock, mind you, but a knock nontheless.  It usually knocked 4
or 5 times, with the first ping being the loudest, and then decreasing
in intensity.  However, I could feel acceleration suffering as the
knock sensor retarded the spark until the knock was gone.  Since I
was skeptical from the beginning that regular gas would work in an
engine with 9.2:1 compression, and I *ALWAYS* :-) accelerate hard in
second gear, I just switched to premium gas and never thought about it
again.  The dealership warned me that using premium gas would be hard
on the catalytic converter, espcially during cold starts, and this
has been confirmed by several magazine articles.

If yours pings continuously without the knock sensor ever retarding
the spark, then a new knock sensor might be in order.  Knock sensors
used to be (I don't know if the Miata's works this way) basically a
microphone bolted up to the engine block to listen for pinging, causing
the engine management system to retard the spark until the knock was no
longer heard.  Consequently, knock sensors break, go bad, become
disconnected etc.  and need replacing.

Hope this helps.

Steve Grossman
Software Engineer
Storage Technology Corp.