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Where does the tachometer get its signal from?

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Old 07-29-03, 07:45 PM
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Where does the tachometer get its signal from?

I am trying to make some RPM activated switches, but I need to know where to get my signal from.

Some info on what the signal will look like would be helpful as well.

Thanks,
Jason
Old 07-29-03, 07:46 PM
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leading coil, I 'll go look for you on my car if you want, but you should look in the fsm.
Old 07-29-03, 07:47 PM
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Actually it taps off the trailing coil pack...
Either trailings or leadings have a female bullet connector which you can tap for a tach signal.


-Ted
Old 07-29-03, 07:51 PM
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Ted is right, all electronics (like cruise, gauges, power steering, etc) requiring a tach signal in the FC get the tach signal from the trailing coil pack
Old 07-29-03, 07:56 PM
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My tach starting not working properly, so I took it down to the mechanic, he said that it was the leading coil. there are actually two leading coils and an ignitor. each leading coil is $125, and the ignitor is $500 OEM. you can also buy it in a package... not sure on the cost.
Old 07-29-03, 07:57 PM
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That was fast

Do any of you know what the signal looks like?

Thanks guys.
Old 07-29-03, 08:10 PM
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Standard tach signal, which is a "pull down" square wave.&nbsp Sorry, I can't give you duty cycle or pulsewidth times...

-Ted
Old 07-29-03, 08:26 PM
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Duty cycle is no big deal.

So it is just a simple square wave?
Old 07-29-03, 08:47 PM
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Yes, like most tach signals, it's a "negative" square wave...


-Ted
Old 07-29-03, 11:47 PM
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stock7....ditch your mechanic. He's taking you for a buggy ride. See http://www.teamfc3s.org/info/articles/demystifying.html and or the schematic https://www.rx7club.com/forum/attach...postid=1398836
Old 09-02-03, 08:33 PM
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Originally posted by RETed
Yes, like most tach signals, it's a "negative" square wave...


-Ted
Cool.

Howmany Pulses per revolution? 3? 6?
Old 09-02-03, 08:39 PM
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I believe the trailing pulses are 3 per full revolution.
Old 09-03-03, 12:52 AM
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Originally posted by stock7
My tach starting not working properly, so I took it down to the mechanic, he said that it was the leading coil. there are actually two leading coils and an ignitor.
Yep, fire that mechanic, he's very wrong. The tach is driven by the trailing coil as mentioned; plus the leading coil is one double-ended coil with one ignitor. It's the trailing coil that's actually two seperate coils with two ignitors.
Old 09-03-03, 02:02 PM
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Originally posted by eyeoutthere
Cool.

Howmany Pulses per revolution? 3? 6?
Revolution of the e-shaft?&nbsp One.
Revolution of the rotor?&nbsp 1/3rd.

It fires like a 4-cylinder, I believe, so it's one pulse per 1 RPM.



-Ted
Old 09-03-03, 07:54 PM
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Originally posted by RETed
Revolution of the e-shaft?&nbsp One.
Revolution of the rotor?&nbsp 1/3rd.

It fires like a 4-cylinder, I believe, so it's one pulse per 1 RPM.
Are you sure?

How many times does any one spark plug fire per revolution of the e-shaft?

Once right?
Old 09-04-03, 03:21 AM
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A single rotor fires once per revolution. So a 2-rotor fires twice per revolution, same as a 4-cyl.
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