VSS problems

[Tedscj at aol.com]

Hi,
I just got and installed a VSS sensor on my car.  It is a four pulse sensor
and also facilitates the attachment of a speedo cable for my cable driven
speedo.
The EFI system I'm using is a 7730  6cyl DIS system from an '89 corsair with
stock (but updated) EPROM.  The transmission is a 700r4 from an 88 Astro.  I
am using the original cable drive gears in the trans.
The problem is that my scan tool is only reporting about 10mph when I'm
actually doing about 60mph, and about 5 when I'm going 30, etc.
My speedo is still reading the proper speed, so I know the cable (and thus the
VSS) is spinning the correct speed.
My manual states that the computer requires 4000 pulse per mile, so I know I
have the right sensor.
Why is the sensor so far off?  Is there something I'm missing?  Are the VSSs
supposed to spin 6x faster than the cable driven speedos?  And if so, why do
they even bother making aftermarket VSSs like this if they won't even work
with cable driven speedos?
I also checked the harness and there is only .4 ohms in each wire from where
ii connects to the sensor to where it plugs into the ECM, so I don't think
thats it.
Does someone know of a way to test the sensor on the bench to see if its
working properly?  I had to "modify" it to make
it fit, so I can't return it (and it cost me $60!)

Thanks for any ideas,
Ted