speedo signal specs

[Jeff Bromberger]

I've got a '94 Z28 w/6-speed. the pcm is calibrated for 3.42 gears and i
have 3.73s. i'm wanting to convert the signal from the pcm to the dash to
compensate for the gears. I'm planning on using the freq-to-volt change volt
volt-to-freq type of circuit. my question is, has anyone scoped this signal?
i know the pcm puts out 4000 pulses per mile but is it a 0 - 5 volt square
wave? 0-12V? My car isn't driveable right now so i can't check it out on
mine. How sensitive is the speedo to its input? does the duty cycle of the
wave matter or is it just triggering off of rising edges per second?

thanks!
jeff

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