jacobson@fluke.UUCP (David Jacobson) (01/29/86)
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
phil@amdcad.UUCP (Phil Ngai) (01/31/86)
In article <1098@vax2.fluke.UUCP> jacobson@fluke.UUCP (David Jacobson) writes: > It never knocks during >ordinary operation, except when in too low a gear, which I always correct >promptly. Well then, you don't need a higher octane gasoline. The only reason for higher octane is to eliminate knocking. More is not better. -- Phil Ngai +1 408 749 5720 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.dec.com