Multi Coil Setups

[Nicholas Parker]

Hi,
     I want to use 4 ignition coils for my 4 cylinder application.  I have
designed an ECU that uses a single 'output compare channel'  to produce four
negative going pulses (one every 180 crank degrees + advance retard offset
etc) that I am de-multiplexing to one of four coils (via driver etc) .  At
present all coils are always on except the one that is making a spark, which
is off for only 2ms then back on until it's cyclinders next spark - another
720degs approx
Is it possible to leave the coils on permanently (except for a spark 'dwell'
/ coil off period of say 2 ms for every spark  ) ?  Obviously the highest
rpm is limited with a fixed dwell like this to speeds where engine
revoultion takes more than  4ms a revolution.
Is using a Ballast resistor to limit coil current o.k? Or will this
compromised the coils 'spark ability' given that it's 1/2LI^2 energy will
not be able to be at the coils maximum...after all the point is for me to
build a GOOD system.

Cheer Nick.
'87 Supercharged MR2

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