Re: Knock sensors

[ptimmerm@mashtun.jpl.nasa.gov]

Youu confusion is understandable

knock = ping = pre-detonation

A little definition will clear everything up.
pre-detonation is when the fuel air mixture
accidentally ignites prior to the intended
ignition time.  So you got a piston racing up to
compress hot fuel and air, and if that sucker
ignites, you got a collison between an unstoppable
force and a moving object. 

You are still technically correct in saying, hey,
what does accidental spontaneous combustion have
to do with ignition timing.  Aren't we talking
sans spark plug ignition.

Here's where I walk out on a limb.  I think that
you are dealing with a wave propagation / timing
issue.  The speed of a mixture combusting may vary
Say a nice smooth gradual wave that just hits
the top of the piston as it heads back down.
If you have a hot, highly compressed mixture, it
may propagate too quickly, and hit the piston while
it is stationary or even moving up.  Thus a mild or
severe pinging.  Listen for the first, act fast,
and you'll never see the second.  We need a combustion
engineer at this point to tell me where I'm wrong.
Anyone from ford.com or gmr.gm.com out there?

So if you sense it as it just starts, and back off,
you can run right up against the limit and never
ping twice in a row.  6 degree retard in one engine
cycle would seem to be pretty darned fast, but nothing
for a computer.

If I am wrong, please be gentle  :-)

paul t-