Hello all, I have an 87 IROC-Z28 350 TPI that I am having problems with. I have been having troubles with my speedometer. About a year ago I had to replace my speedo cable because it broke off in side the cable. After I replaced that I had to fix a slight cable lubrication problem (grease inside the cable) I fixed that and that fixed the irritating lurching I was having from the bouncy speedometer. Now I am having the lurching again but the speedometer doesnt move around like it did. I hooked up on of those scan tools to the computer and everything seemed normal except for the Vehicle speed reading. Its all over the place like the cable is bobbing around. I know this isnt the case because I can see it doesnt budge at all. Keep in mind this problem just happened about 6 months after I fixed the cable. Anyway, Im pretty sure its in the VSS system part of it. I guess what I am looking for from the infinate wisdom of this board (sucking up) is where are these sensors located???? I have read that there is a Vehicle Speed Buffer behind the Speedo but is there any other sensor like inside the transmission or anyother place that reads this infor for the ECM? If there is where can I locate it at on the car and where can I find a new one? What are my options cause its really irritating. My torque converter locks up too quick and it launches hard. I know it doesnt do it when its cold I assume since the computer is in closed loop till its warm. Please help. I dont know what else to do.... Thanks!!!





Rick

 

Your 87 IROC should have a mechanical speedo. The VSS has nothing to do with the function of the speedo, it only reads pulses from the rotation of the cable to send data to the ECM. You more than likely have an overgreased or kinked cable or possibly a stripped speedo driven gear in the tranny.

 

My problem isnt in my speedo cable. My trouble is the data that is being sent to the computer. When I hooked up the scan tool the readings to the computer were jumping all around. Yet my speedometer is goes up and down nice and smooth like it did when it was new. So That rules out the over greased theory and the kinked cable and the stripped gear. I know its a computer sensor problem. I just need to know where the VSS is located. Im sure it will fix my problem if I replace it. The "pulses" to the computer are all out of wack.

 

The VSS sender for your model is in the speedometer head itself. If you look at the back of the speedo you will see small wires coming out of it, that is the VSS signal wires. From what you describe you may have inadvertenly caused a problem with the wiring when working on it. LOL