My Electronic Speedometer (145 MPH) is no longer working.

Over Winter I swapped out my 350 TPI to a 383 carb as you can guess most of the sensors did not go back on the 4-bolt truck block. ECM is left intact and wires that use to run under the hood (injectors, sensors... etc) for it are all tucked inside fender opening.

VSS in transmission was not messed with.

Main bulkhead connection for power and accessories was removed for cleaning and painting purposes then reassembled after going through a electrical cleaning.

Rest of guage cluster has power and works, besides water temp/oil pressure (I replaced those with autometers.)

Next time I'm back to the car I'm going to check my VSS wiring at the transmission tailshaft. Any sugguestions on other places to look?

 

its the green with black stripe coming out of the computer then goes int a yelow vss box the controls cruise , just connect the g/b from the dash to the tranny output. coolant is dkg coming out of the driver side firewall along with tan which is oil pressur

 

I never unplugged anything in the dash or on the computer side. I'm thinking I just did not get a ground reconnected under the hood. Guess I'll go back and sort through that rats nest.

I should have stated the last bit better. My coolant and oil pressure work. I simply ran new wires for that.

 

well if u went from fi to carb the computer is no longer used , so u need to connect the vss wire from the tranny to the cluster which u can locate on the pass side underdashif u find that wire tap it with a test light and the speedo will move

 

Hey what if my speedo is showing lights and jumps to diffrent MPH then goes back to Zero what could cause that. It works but jumps to diffrent numbers never the right MPH while im driving.

 

Both of my 3rd gens have had this problem at one time or another....

Checking at the vss connection is something worth doing. For some reason, this simple connection can be finicky and cause intermittent shorts which shows up as working / non-working speedos and or as a non-functioning speedo. While under the car at the connection, inspect the wiring for damage.

To ensure that the loop is good to the ecm, pull it from the dash, disconnect the harness and loop test the purple and yellow back to the vss to make sure the connection is good. I've had to install a zip tie on the vss wiring connector to keep it tight enough to keep the thing working!

Hopefully, that will be the problem. If not, at least you can dismiss it and look elsewhere... Perhaps at the pig tail connection on the back of the cluster? If it's not seated good or the harness is pinched, it'll also cause headaches and similar problems, believe me.

Good luck

btw, in case you might be wondering about my sig. my 87 IROC also has an electronic speedo & dash out of a 91Z

 

Ok, I have ECM pulled now to test it.

I don't know why everyone keeps on telling me to check the VSS Buffer Box I can't seem to find it anywhere and after searching here I found out the 90-92 Speed Density TPI motors had it built into the ECM.