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Old 02-13-2018, 03:07 PM   #47
40 Deluxe
Senior Member
Join Date: May 2010
Location: now Kuna, Idaho
Posts: 2,798
Default Re: Replacement Ignition Coil

Originally Posted by duke36 View Post
See the attached article though not sure how much science data is involved.. Perhaps it will help with Bob's initial ?. Note the sentence that the 2ndary output is around 100 x the primary voltage with other parameters in force as well.
One point not addressed in that article is the great variation in secondary voltage output. As the primary field collapses and induces secondary voltage, secondary voltage only rises to the amount needed to jump the plug gap. If 5,000 volts will fire the plug, that is what the coil produces, no more. If it takes 10,000 volts to jump the plug gap, that is what the coil produces. During my career as a mechanic, I've had many vehicles hooked to a scope and seen this. A fouled plug or a plug wire shorted to ground shows a very low coil output. An open plug wire or worn plugs with large gaps show higher output voltages. We also did a 'snap test', snapping the throttle wide open quickly. This also raised the voltage requirement significantly. If one cylinder showed an abnormal spike, it was the problem child.
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