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Thought for the day.................

To: Barney Gaylord <barneymg@ntsource.com>
Subject: Thought for the day.................
From: neil.cairns@virgin.net
Date: Sat, 08 Aug 1998 08:24:25 -0700
Barney Gaylord wrote:
> 
> Thought for the day (waxing philosophical):
> 
> In a message dated 8/7/98 3:13:40 PM DANMAS writes:
> > You are right, the coil itself is not polarity sensitive; However, the
> spark plugs are, and, .....
> 
> Given due consideration, the polarity of the spark plug is probably not
> very important.
> 
> Many newer cars have distributorless ignition systems with multiple coils,
> where one coil fires two spark plugs at the same time.  It's called a
> "waste spark" system, where one plug fires on the compression stroke as
> normal, and the other plug fires at the same time on the exhaust stroke
> (wasted spark).  Older single coil systems pass the spark from the coil
> (via the distributor) through the spark plug to ground, and the high
> voltage circuit is completed by the body of the coil also being grounded.
> 
> With the waste spark system the body of the coil is not grounded, but the
> high voltage side of the coil completes the circuit by being connected to
> two spark plugs, both of which are grounded.  The spark goes from the coil
> through one plug to ground and then from ground through the other plug back
> to the coil to complete the circuit.  If you pull one plug wire, two plugs
> stop firing.  In this case the two spark plugs are opposite polarity, and
> it doesn't seem to affect the spark quality or the life of the plugs (at
> least not enough to bother anyone).
> 
> And if you're worried about that wasted spark wasting energy or degrading
> the spark plug, it does neither.  Since the two spark plugs are in series
> with the coil, the same current passes through both plugs.  The plug firing
> on the compression stroke requires a lot of voltage to make the spark jump
> the gap under pressure, while the plug firing on the exhaust stroke takes
> very little voltage to fire.  As a result, most of the energy of the spark
> is going to the plug doing the useful work, and very little energy is going
> to the idle plug.  So not much energy is being wasted, and that little
> energy being passed by the idle spark plug causes very little wear on the
> plug.
> 
> Just one of our modern day curiosities, but it does show that modern day
> designers have determined that the polarity of the spark plug is pretty
> much irrelevant.
> 
> $.02,
> 
> Barney Gaylord
> 1958 MGA with an attitude
> 

>   BG

I learned about this ignition system the hard way, whilst checking if an
oxygen sensor was working. I took off a plug lead to deliberatly muck up
the mixture, ( on a modern Ford Escort,) and was astounded when the
thing clattered away on two cylinders only, just!

If you are a 'little behind the times' on all this stuff, get the book
Auto Elect Systems by Tom Denton, from the library, ( he is Australian I
think,) ISBN 0 340 58604 4. I found it good reading, AND easy to
understand. " Distributorless Ignition" is the chapter about this.

Neil

PS.
Why do I always ger the 'elderly male' driver in a Triumph Aclaim/Honda
Accord/Rover 200, ( all the same car...) infront of me, doing just
35-40mph??? Why always ME! UK roads are rather bendy, and it takes nerve
to thunder past on blind bends in an old MG. Actually I do not mind, but
it scares the pants off the wife!!!

NC

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