Ignition module

Steve Baldwin steveb at kcbbs.gen.nz
Mon May 15 13:48:06 GMT 1995

Paul raises quite a few points that I would like to comment or expand

Firstly, I agree about the amount of CPU power required. As far as a
micro is concerned there is plenty of time to think about what to do
next. Even a V8 at 8000rpm is only firing every couple of milliseconds.
If you take 100us in an interrupt routine to act on this, that still
leaves 95% of the time to decide what the values should be.
I'm curious about the application of fuzzy logic in engine control and
_may_ experiment in that area. Even so, given the assistance of a TPU, I
would expect the 332 to be over CPU'd unless you are really trying to
model the engine down to the tiniest detail or control a lot of other
systems with the same CPU.

Knock detection.
I'm interested in hearing more on this. The recent discussions on spark
plug current flow were another area I had been planning on experimenting
with. However, a bit more reading later and I'm no so sure. From what I
have found out so far, it seems to be an ideal way of determining pre
and post ignition but not knock. If pre or post ignition is detected,
you can dtermine that the risk of knock is very high but that is all.
My understanding of 'knock sensors' is that they rely on the resonant
frequency characteristics of the block. How make specific is this ?
Since my testbed engine is a pre-war flathead, I doubt there is
manufacturers data and I'm a little reluctatnt to determine knock
characteristics by experiment.

Spark duration.
My previous impression was that the longer duration, the better and that
the voltage required was purely a function of the gap  which was as wide
as possible but still mainitained reliable operation in all
circumstances.  This is all still more or less true but, I have since
learnt that the energy transfer during the breakdown phase is
substantially higher than during the sustained phase. This and the fact
that plug wear and heat buildup occur in the later phase, makes me much
more in favour of the MSD approach.

I guess this is best determined by measuring the plug resistance. Keep
adding spark until there is no more burning.


More information about the Diy_efi mailing list