Knock sensor control (and other uses for ionization gaps)

[Matthew Lee Franklin]

>This ion gap sensing sounds pretty good. My question is whether the current
>change due to gap erosion is corrected for. Seems that after a few thousand 
>miles the sensor would start reading less ionization due to the rounding off of
>the center electrode.
>
>Millam E. Tackitt

Good thought, but maybe the thing to look for is a signature or shape of a 
type of event such as a misfire or knock rather than the absolute current 
level.  Granted, the absolute level really does matter, but within wear 
limits maybe you'd find an OK compromise.  

I suppose other things might affect the absolute level also, such as fuel 
composition (ethanol, MTBE, or more minute additives).

Later,
Matt