From: Sergio Dimarmo
>I just installed EI on my car and want to make sure my tach is correct.
>I'm planning to change the parts mentioned by Jarrid on one of his
>posts. I have a Sears tach/dwell/volt meter but I'm not sure how
>accurate it is. Would it be possible to caluclate the pulse generated
by
>the coil and using an oscilloscope, calibrate the tach?
Using a scope, put the scope on an input mode that will allow 300v DC.
Connect the common on the scope to ground, and take the scope input
to the - lead on the coil.
Never touch the coil- lead, it will shock you something fierce.
When the points close "or transistor" the scope will show close to
0v, but when the points open, the scope will show a brief peak to
about +200v, then decay to +14v.
Trigger on greater than +20v on the rising edge, and set the time base
to 5ms per division.
Set the idle until the rising edges are 30.0ms apart. "Ign_Interval"
This will be 33.3hz, and correlates to exactly 1000RPM."Ign_Freq"
Set the adjustment on the back of the tack to match this rate.
For verifying higher RPMs.
Ign_freq = RPM / 30 "Only for 4 cyl"
Ign_interval = 1/Ign_freq.
Jarrid Gross
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