GM VSS inputs

[grobbins]

Does anyone know if I can use a reed switch type of speed sensor
as a signal for the GM LT1 PCM (or Ford 5.0 EFI) control units?

This OEM reed switch signal comes from inside the speedometer
head. The switch cycles 4 times per revolution of the speedo
cable, with one leg connected to ground. The OEM uses this speed
signal for their ECU, cruise control, auto adjusting suspension,
and speed sensitive power steering.

Another question....should I be overly concerned if the above
produced a slightly non-standard rate? Based on the OEM's speedo
standard of 1025 rev per mile, the rate would be 4100ppm to the
PCM, instead of the 1000 rev per mile / 4000ppm spec'd for the
Chevy.

The current method to make everything work is to install a
conventional 4 pulse signal generator into the speedo cable for
the Chevy. If I have to, I can manipulate that signal w/ a
digital ratio adapter. I'm not yet sure if I can easily use the
same ratio adapters to modify the reed switch signal for the
PCM.....

Grant



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