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
PS (bitch time)
Recently had to replace the ignition module on the 1990 Chevy Lumina, cost
$130 at the cheap store. Add three coils at $40 each and a $50 hall effect
sensor, and the cost of spark comes to at least $300. And by my
considerable experience with used cars of the appropriate age, the solid
state ignition module has a life expectancy of no more than 10 years. When
it does fail, it's guaranteed to leave the car stranded on the spot,
probably requiring a tow as well as the expensive part. Personally I'd
rather pack a $4 set of contact points than one of those ignition modules
and a hall effect sensor.
BG
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