I have an '87 Formula, and it has the single pod electronic gage cluster. All of the gages except the speedometer work fine (though the fuel gage doesnt always read correct). if anyone has any ideas as to what it might be please let me know!

 

Have you checked your fuses yet? I removed my ECM from my car and my speedo stopped working. I had to put back a piece called as pre-buffer or something. Now it works fine. It could be one of those things but I'm not real sure.

 

Last time i checked all of the fuses were in place and a-okay. I got my car with a shot trans and recently had it rebuilt so i was never able to drive it before-hand. I'm trying to contact the previous owner to ask him but so far no luck. Just out of curiosity, where is this pre-buffer located and how much did it cost ya?? Thanks for the help.

 

All these cars used an electronic VSS (Vehicle Speed Sensor) which sends a signal to the ECM, and then the ECM sends a signal to run the speedo and odo.

Going through this exact same problem right now with my 91 GMC Jimmy I will STRONGLY suggest you beg borrow or steal a scan tool and see things like the ECM is seeing them. If the ECM shows correct speed on the scan tool then you know the problem is either the ECM not ouputting the correct signal to the gague cluster OR the gague cluster is shot. If the ECM isn't registering the correct speed then it's probably just a bad VSS sensor (cheap fix- $26).

In my case, the ECM showed correct speed, ruling out the VSS, so I tried the next logical thing- replacing the ECM (in case it was not outputting the correct signal to the speedo/odo). No dice. Now I'm down to the speedo-odo being bad (which is what I thought it was from the beginning).

If your odo is still working but the speedo is not then it's dead-bang and bad gague. The ECM's output runs both the speedo and odo. So if one works correctly and the other doesn't then it's got to be a bad gague, since they both run off the same signal from the ECM.

Things were much simpler when there was a physical cable that ran from the tranny to run the speedo and odo. These later systems you need to do some diagnosis or you'll throw parts at it for weeks.

 

i have a stand alone VSS system no ECM for me :-D the sending unit in the trans has a gear make out of plastic and that like to strip out some times. i'd look at that last but its an idea to keep in your head

 

My speedo just died on me as well. There are two gears that run the speedo. One is on the tailshaft of the tranny, and the other is on the sending unit. What caused mine to die is that the little metal clip that holds the gear on the tailshaft of the tranny (drive gear) in place broke or came loose. Now the drive gear is loose in there and isn't turning the other gear. If this is your problem, your gears may have gotten a little chewed up too, mine did.