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Path: utzoo!watmath!clyde!burl!ulysses!bellcore!decvax!tektronix!uw-beaver!fluke!jacobson
From: jacobson@fluke.UUCP (David Jacobson)
Newsgroups: net.auto.tech
Subject: Super Unleaded necessary?
Message-ID: <1098@vax2.fluke.UUCP>
Date: Wed, 29-Jan-86 14:32:32 EST
Article-I.D.: vax2.1098
Posted: Wed Jan 29 14:32:32 1986
Date-Received: Sat, 1-Feb-86 04:51:28 EST
Distribution: net
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 38

The other day I had my '84 Nissan Sentra at a radiator/muffler shop getting
a new muffler.  As the mechanic, who seemed quite competent, was backing it
off the rack, he asked me "Are you burning regular unleaded in this?"
"Yes", I replied.  "Well, hear that noise?", he asked as he revved the
engine a sharply, but backing off before it got going very fast.  I heard
about 250 milliseconds of mild clatter just as the engine first increased
speed above idle.  He repeated the demonstration.  "Well, that's
detonation", he went on, "and if it continues, sooner or later you will
have a hole in a piston.  You'd better switch to a super unleaded before
that happens."

Is he right or not?

Here are some facts.
The engine is a 4 cylinder OHC engine constructed of aluminum.  The
displacement is 1597 c.c. with a 9.4:1 compression ratio.  It is the
standard US model (not California) with a computer under the front seat.
According to the schematic the uP has the following inputs:

	- water temp sensor
	- barometric pressure sensor
	- air temp sensor
	- exhaust gas sensor
	- clutch/neutral switches (2 switches in parallel)
	- throttle valve switch
	- vehicle speed switch
	- crank angle sensor (actually 2 distinct signals, 1 gives 360
			pulses/camshaft revolution, the other 4)

There is also a vacuum switch; it only operates a "vacuum cut solenoid" and
doesn't go to the uP.  I had thought that it had some kind of knock
detector, but after searching the schematic, I can't find any such thing.
It is supposed to idle at 800 +/- 100 RPM, but I recently checked it and it
was only about 650.  I didn't bother changing it.  It never knocks during
ordinary operation, except when in too low a gear, which I always correct
promptly.  It has 18000 miles on it.

  -- David Jacobson    ...ihnp4!uw-beaver!fluke!jacobson