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Posted by Paul B. (more from Paul B.) on Sun, 20 Oct 2002 17:06:27 Share Post by Email
In Reply to: Re: Au contraire, J, Sun, 20 Oct 2002 14:36:17
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Now don't get upset, but the way I see it is this:
Its the turns ratio between the primary and secondary sides of the coil that determine the voltage that the spark plug sees. For the same voltage supplied by the ECU to the primary side there will be only one voltage value on the secondary side. I don't think the ECU is capable of varying the primary voltage according to the voltage required to jump the spark plug gap, but I could be wrong.
With regard to the power in the circuit, I believe it can be defined in terms of current since V=IR (Ohms law)and you can substitute IR every where that V appears in your equation. I don't think there is any power being dissipated if no current is flowing. As an example your toaster only makes heat when electrons flow (current) from your wall outlet through the heater wires to ground. If you unplug the toaster the voltage present in the wall outlet does not cause the outlet to overheat because no current is flowing. Higher voltage will result in more current flow and more power if the resistance remains constant, but a wider spark plug gap creates higher resistance and less current flow.
What I think may be a possible cause for the DI failures is that the insulation in the secondary side of the circuit may breakdown when the spark plug gap gets large enough that the spark doesn't have enough potential to jump it, and the high voltage is seeking a lower resistance path to ground. If the insulation breaks down there will be increased current flow to ground (a short circuit), and you will get heat, smoke and that nasty burning smell.
Only my opinion, based on some rapidly expiring brain cells.

posted by 64.252.234...

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