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Old 09-15-2007, 09:31 AM
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Pulsed Signal on Tach wire

Hey guys, I have a '85 Camaro, 305. Does anyone here know what signal is on the tach wire from the distributer? I know its a pulsed output, but is it pulsing off one contact, like one pulse per engine revolution? Or is it one pulse per contact (eight pulses per rev.?) I can't start my car at this time to measure it.

Thanks for any info

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Old 09-15-2007, 09:44 AM
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Should pulse for every cyl fired...
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Old 09-15-2007, 12:54 PM
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That sounds right. In searching I've found that aftermarket shift lights have a setting for 4, 6, or 8 cylinder engines, so the signal must be different for each, hence 4, 6, or 8 pulses per rotation... right???
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Old 09-15-2007, 01:07 PM
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Correct, in reality the tach wire connects to the Neg side of the coil and senses the voltage drop when the coil releases its energy. thus 4 releases per turn on a V-8, 3 for a V or L6 and so on. Because only half the cylinders fire on each revolution.

This is my understanding on it anyway.
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Old 09-15-2007, 01:50 PM
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Ahh, ok thanks, 4 pulses per rev. makes sense! Thanks so much for the help!!!
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