VSS signal to ECM

[Kovmat]

I am finally getting around to wiring my Hybred project. I want to make sure I get the signal right going to the ECM to indicate the veichle speed. I have a mechanical speedometer that is calibrated at 1000 revolutions per mile. If I understand correctly, the signal coming into the ECM is supposed to be 2 pulses per revolution. Is that based on 1000 revolutions per mile or 2000 pulses per mile?

Also, does anyone know what the pulse width is supposed to be to operate properly?

Thanks,
Matt

 

[RmvBfrFlght]

The pulse width isn't that important. The proper signal is 2K PPM, it is an open collector output from the buffer to the ECM input.

The stock Buick VSS set up is an optical reflection from a bar on the back of the speedometer head. Each revolution of the speedometer cable provides 2 reflections off of the bar. So 1000 rev's per mile becomes 2000 pulses per mile to the ECM.

RemoveBeforeFlight

 

[Kovmat]

Thanks for the reply, sounds like you have a pretty good understanding of basic electrionics. I used to dabble in electronics years ago and know just enough to be dangerous. I have one of those autometer Hall Effect senders that puts out 16 pulses per revolution. The plan was to use JK flip flps to divide the frequency and then use a 555 timer to control the pluse width. If my math is correct, the pulse width will vary from .18 seconds @ 5mph to 0.0075 seconds @ 120mph. If the ECM can handle a range like that than I don't need the 555 timer.