I need to know how to get a correct signal to a 165 ecm to let it know the vehicle speed. Right now it appears the recalibrated speedometer threw the whole factory VSS garbage all out of whack, so I have to try a different route.

I figure my choices are to somehow create a circuit to send the correct signal to the ecm now that I have messed up what was working before. Is this even possible? Does anyone know what kinda signal it sends to the ecm? If its something beyond a linear voltage signal I think I might be screwed since I know just enough about electrical circuits to get me into trouble.

The only other thing I can think of is that Cyberdyne (or whatever it is) box that attaches where the speedo gear is, and use that to send the ecm the info. Think that will work? Is it adjustable?

Just as a FYI, this is on a Grand Prix with a 2004r tranny and the VSS is behind the dash on the speedo.

 

I'm guessing you had the speedo recalibrated to compensate for altered rear-end ratio? What I plan to do to get an accurate reading on mine after the 3.08 to 3.27 rear end swap is leave the speedo itself alone, and take the car to United Speedometer and Instrument here in Riverside. For about $130 they'll put together a conversion box that'll go between the two sections of speedo cable before the speedo itself. That method is effectively the same as putting the correct gear in the trans output shaft, so it shouldn't affect the VSS at all. If the speedo cable isn't 2 piece in a car, they put the box between the cable and the trans itself.

 

The gear was changed, but we took care of that in the tranny. The speedo was repainted and recalibrated so that it didnt read only to 85mph, it now reads double that.

 

Ahh, I can see how that would screw up the VSS. It thinks you're going as fast as the old painted-over numbers that the needle is pointing at. The only thing I can think of is to have a new chip custom burned that reads the VSS signal to match what you're doing now. Instead of 20 pulses per second meaning 40 mph, it now reads 20 pulses per second as 20mph. (if it uses pulses that is...)