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'[EE]: Boat engine brainstorming'
2001\10\17@100856 by Dennis Noordsij

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Hi,

I've been wondering about this idea for a while and would like to hear some
criticisms/suggestions regarding the following :)

I have a boat together with a friend here in Finland which is about to be
winterized, during which (and the almost entirely dark days and way too much
snow :-( there is not much else to do than bugger around with projects :)

The boat is a 6.20m long Finnish design (Flipper 620), and the engine is a
1979 Johnson 85hp 2-stroke, which is quite reliable once it's running, a bit
tricky to start, but would be much more useful if we could monitor and
control more things automatically and electronically.

The first example is the situation "why doesn't the damn thing run!". It
needs a) fuel, b) crank and c) spark. Crank is done by an electric motor and
using an RPM meter you can tell if it is cranking fast enough to start
(>1000rpm), fuel is usually there except when the plugs are wet and there is
too much fuel. This is then related to the sparks, because wet plugs don't
spark, which leads to the desire to be able to automatically distinguish
between:
1 - no spark, no attempt to spark, i.e. distributor problem
2 - attempted spark, i.e. distributor is working but no actual spark is
created due to for example wet plugs or faulty cable.
3 - proper spark, distributor working and spark plugs creating sparks.

To put things in the simplest way I guess:
1 - no voltage potential occurs between spark cable and ground, no current
flows
2 - there is a voltage potential at the spark intervals, but no current flows
(no spark to ground)
3 - there is a voltage potential at the spark intervals, and (a little)
current flows when the spark bridges to ground.

What would be the best way to measure these situations? I guess you can
distinguish between 1 and 2 using a wire wrapped around the cable similar to
AC detection circuits that work just by holding it close to the wire. To
distinguish between 2 and 3 you need to measure current flow (only in a
yes/no way) but because the voltage is quite high (though I don't know in
what ballpark it is) and the current is quite low (again, no idea what it
actually is :-) I don't know what would be the best way to tackle this. Maybe
there is a much easier way?

Any ideas? :-)

Kind regards
Dennis

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2001\10\17@160610 by Mike Hardwick

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Dennis,

Just an idea... It's been a long time since I've done any of this, but I
recall that engine diagnostic oscilloscopes can readily distinguish between
various ignition system faults. Perhaps you could get hold of an operator's
manual for one of these instruments, and learn the details. I have a manual
for the old (~1972) Heathkit CO-1015 Ignition Analyzer. It has a short
chapter on ignition analysis that looks very informative.

Knowing what the waveforms *should* look like, and how to acquire them, you
may be able to devise an automatic test system that's simple enough to
leave in situ. This sort of thing has been done before, in LAN testers that
use TDR for cable analysis. They don't actually display TDR waveforms, just
distance to fault and type of fault (open or short).

Mike Hardwick
Decade Engineering



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