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Old 03-16-2017, 11:41 PM   #324
bobxyz
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Join Date: Aug 2014
Location: Boulder, Colorado
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With each pair of plugs running wasted spark, the spark on one plug always jumps normally and the spark on the other plug jumps in the opposite direction. For instance, in the 1-4 pair, #1 will always jump normally center to outer electrode, and #4 will always jump backwards outer to center electrode. The path of each spark will be the closest point between center and outer electrodes.

If you can find diagrams that show the internal wiring of an old fashioned single coil (used with a distributor), you'll see that one end of the primary and secondary windings is connected together. This is the return path for the spark energy. With a wasted spark coil pack, the two ends of the secondary winding are connected only to the spark plugs -- the coil gets charged up, the primary is disconnected, and the collapsing magnetic field generates the spark voltage across the secondary. To discharge, a spark needs to simultaneously form on both ends of the coil to complete the electrical path.

I've read the claims that special plugs are needed for wasted spark but I don't get it. Platinum plugs have a shortened center-to-outer electrode path such that the spark is always on the platinum. This allows the plugs to last for 100K miles. If you're going to inspect and change your plugs more frequently, standard copper plugs are fine for wasted spark. (I guess the sharpened electrodes on a platinum plug might be a bit better if you're fowling plugs.)
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