In my circumstance using code59 with a 730 ecm as well as for general engine management, a speed signal is crucial or at least very helpful for many ecm functions; boost vs. mph, decel, fan control, shift light, lean cruise mode, etc.
I'll post the specifics in brief form.
Make sure you have magnetic sensor use selected in the bin.
If you are using code59, the ecm is to be wired as a 749, but the vss part should be wired according to 89-91Chevy Beretta specs across B9, 10 and 11. B11 being your 4000ppm output to the odometer. The 749 diagram only shows a vss input from the DRAC at C6 and it did not register a speed in the datalog when connected to the SGI unit when I tested it (Because it is intended for the optical speed sensor).
Although the instructions for the SGI-5 indicate you can adjust speed up or down by simply pressing the up or down buttons I observed no response during a datalog while attempting to do so.
A Dakota tech stated I would need a "pullup" for the signal into the ecm. He suggested a 1k-10k ohm resistor between 12v and the vss signal going into the ecm. I used the circuit by Darth since it was already in the car and a little more sophisticated. I confirmed that the pullup cirucuit is indeed required for the ecm to sense the vss signal from the SGI in this configuration.
The settings for the SGI-5 using stock size tires 215/60R15 are as follows:
Set switches #3 and #4 to the on position.
Preset the SGI unit per unit instruction sheet to calibration 9,3, representing a calibration of 2.024, via the up/down buttons.
Use "OUT4" as your signal source.
I checked the above against a GPS reading and my speedo read right on target plus 2 mph for human error in reinstalling the gauge needle after the raw F40 vss signal violently shook it off the dial. It reads on target in the ecm.
The above configuration requires TWO pullup cirucuits, one for the signal into the ecm and one for the signal out of the ecm to the odometer.
I mentioned this in a thread on the topic a long time ago, and will do so again here. If you put together your own wiring harness, make sure the wires from the vss sensor to the unit are twisted together in the same manner those from the CPS sensor to the ignition coil are.
My odometer needle swings smoothly, I have observed none of the bouncing/ jumping that some have complained about after using the SGI to calibrate their odometers.
If you're using the more common bin options (Beretta A1 for example or TGP 8F) you will need to set the IP divisor in the code to 0 or 1 for proper output to the odometer, then the road speed constant will need to be set somewhere in the 120,000 ppm range as 4000 ppm setting for whatever reason with the 4000 ppm input to the ecm from the SGI unit is not enough.
Next is the Digital Cruise control.
I used an AR coded module. Some have used modules from trucks but the one I retrieved from an 96 S10 did not work. I noticed it is larger than the AR module which my be a point to consider in choosing a module that does not have the AR code, in other words, avoid the larger size unit.
The signal for the cruise module can be fed directly from the SGI unit output 5, along with Darths wiring instructions.
[This message has been edited by Joseph Upson (edited 05-31-2012).]