Does anyone know what I have to do to make my speedometer on my 1990 IROC work after I yank out my computer from my carb swap? When I pull the computer it kills the speedo. The speedo and tach (which is broken anyhow) seem to be the only things that the computer controlls anymore.

 

Well the computer doesn't have anything to do with the tach, so the good news is that the only thing not working is the speedo, j/k.

The VSS goes to the computer and is then sent to the speedo, so when the ecm is removed the circut is broke so you just need to take the purple and yellow wires from the VSS and run them directly to the speedo.

I don't have any experience with the 90-92 clusters but more than likely there is only one wire that goes to the speedo. I can't remember which wire you can use as a sensor ground I'm thinking the yellow one but not sure. So find out which wire from the VSS you can ground and run the other one directly to your speedo.

 

Is the VSS located under the steering column?

 

Is the speedo 4000 pulses like the output from the VSS is, or is the speedo 2000 pulses? If the speedo is 2000 pulses you cant run it right off the 4000 pulse VSS.

 

That's a good point, I'm not sure about the ppm being different from ecm to speedo. when he hooks it up he'll be able to tell because it will be pretty off.
If that is the case that it isn't reading correctly you'll need to get a signal converter box, digital dakota makes a SGI5C box that t56 swappers use for there vss signals, and that would also take care of the 2 wires from your vss and sending out 1 wire to your speedo. there not to expensive if you do need it, around $70 on ebay.

Also your vss is on your transmission, it will be a plug with a yellow wire and a purple wire comming out of it. Check the link in the stickies called "possible useful link" for an autozone wiring diagram and scroll down to your application it's for firebirds but is interchangeable for our 3rd gens. This will tell you which plug the vss goes into your ecm and you can continue the wires right there to your speedo instead of running new wires yourself.

 

Ok thanks guys!