Vss on 165 ecm help!

[Ludis Langens]

Mike Rolica wrote:
> 
> I have one last thing to solve on my tpi s10 project.  I have a mech
> operated speedo and the prom is for 89 firebird 350 tpi   (apyu)  It has one
> wire -Brown for the vss.
> With the ign on I have 13v nothing connected.  I've tried the optical type
> but most I find are bunt out and I believe they are only dc pulse.  What do
> I need to send to the ecm?  What is it looking for in detail.

The '165 ECM expects to be driven from an open collector digital output.
 The '165 provides a pullup resistor to the battery voltage.  This 0V -
12V - 0V - 12V signal is sent through a 100K ohm resistor, clipped to
5V, and buffered by a CMOS inverter.

If the Firebird has a "magnetic" VSS, then there will be an interface
box between the VSS sensor and the ECM.  This box is sometimes called a
"4-out buffer".  The box converts the AC signal from the sensor to the
digital DC expected by the ECM.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/