Ignition Book

[Dave Williams]

-> system that sounds a *LOT* like the new one from SAAB, which uses
-> "continuous" resistance measurements over the plug gap to determine
-> what to do on the next firing cycle.

 The TAG engine management systems some F1 teams were using five or six
years ago did that, to reduce the spark to the minimum level, much like
the Jacobs units claim to do.  Jacobs claims too much zap will do evil
things to the combustion process, which is dead opposite my own testing
with various coils and ignition systems.  If I had a long enough
extension cord I'd have my arc welder hooked up to the distributor
somehow.

 The only justification I can find for reducing spark energy would be if
the plugs had a rather narrow heat range and tended to overheat at high
RPM unless power was reduced.  It's well known that it's easier to light
a spark at high RPM than low RPM, so you could get away with it.  I'm
not convinced reducing spark energy would cool the plug to make much
difference, though.

 The SAAB Trionic system monitors the resistance across the plug gap to
look for detonation.  It's much more accurate than the usual piezo
sensors, and doesn't require extensive signal filtering.  The later
Trionics can also determine if a cylinder is running lean by monitoring
required spark voltage, and it's also handy for detecting misfire, which
is a requirement for OBD-II.