I just got done converting over to carb and now my speedo doesnt work. I read that 87 was the first year for the firebird to have a electric speedo. What can i do to make it work or do i just have to get the mechanical setup?

 

IIRC, with mine, there was a ground loop under the hood that was originally attached to the block.
All I can remember about it is that it had 2 black wires and it had a large dia "eye" on it.
I grounded that and the instruments came back to life.
Mine wasn't an 87 though.

 

All of my guages work except the speedo

 

Odd, my 92 convered over to carb it still works just fine.

Early cars had an old-style mechanical cable to drive the speedo and it had a VSS sensor patched into it at the back of the gague cluster (if memory serves) to send the signal to the ECM for torque converter lockup and such.

Later cars had the VSS built into the tranny which drove the ECM and then the ECM drove the speedo electronically.

Neither system should be defeated by simply swapping over to a carb. If the later system is used but the ECM isn't functioning for whatever reason, however, the speedo won't work.

 

Did you keep the computer hooked up? I think the VSS sends a signal to the computer and then it sends a signal to the speedo. So if the computer gets ripped out the speedo won't work. At least I think that's how it works on a 92 Camaro like I have. Correct me if I'm wrong.

 

Nope dont have the computer no more. I should have left it. Now i have another question since it has an electric speedo was the ecu calibrating the speedo? As in if u changed rear end gears it would have to be reprogrammed or can u still just change the speedo gear that is at the transmission? If the computer wasnt calibrating it then it could be hard wired. hmmm?

 

all the firebirds from 85-90 use a buffer box to change the speed signal and send it to the cluster, cruise and pcm. that box was mounted on the same bracket as the old pcm you took out

 

You need to change the gears in the tranny or get a digital converter to adjust the signal.