cyberdyne speed calibration box

Joe Boucher BoucherJC at lmtas.lmco.com
Fri Jan 30 17:12:28 GMT 1998


Shannen Durphey wrote:

> 4) modern speed signals, specifically 700R4, 4l60E, are AC, 40 pulses per
> revolution of the driveline.
> 
> 4.5) to find out how many ppm are sent to signal buffer, by 40 tooth sensor,
> divide 5280 by tire circumference in feet, multiply by rear axle ratio, and
> multiply by 40.  A car with 29" tires and 3.72:1 axle produces 103,483.3
> pulses per mile.

This info and calculation are correct, but the in '89 TBI system I
installed in my Suburban, the 103,483.3 pulses are fed into the back of
the speedometer housing where a circuit card converts it into the 4000
pulse per mile, 12 volt signal.  I didn't have the speedo housing and
was getting a no VSS code and no torque converter lockup. When hooked up
to a digital VOM the tranny output would show a rising AC voltage signal
as speed increased.  The speedo housing, VSS output to the ecm on a VOM
would quickly jump up to 6 volts and stay there.  I was told this was an
indication of a digital, on/off 12 volt signal.


Joe Boucher
'70 RS/SS Camaro  '81 TBI Suburban



More information about the Diy_efi mailing list