Well, hell. The black Formula had been running great with few glitches. Then suddenly, the speedometer started dancing around while driving. I put a different 120mph speedo in there, and it did the same thing. Seems steady until about 40mph, then it gets worse the faster I go. No code 24, so something past the point of the VSS or ECM. Any ideas where to start checking the wiring?

The VSS signal wiring starts with the VSS plug and goes to C203 G, C203 R. The signal then goes to the speedo module in the speedo that is grounded thru C203 M, and the 2000ppm signal to the ECU goes to C203 H.

C203 H communicates with the ECU at connector 2, plug A10.

Check the grounding of C203 M and all of the various connectors.
Also check the integrity of the wiring terminals at the VSS plug.

quote Originally posted by olejoedad: The VSS signal wiring starts with the VSS plug and goes to C203 G, C203 R. The signal then goes to the speedo module in the speedo that is grounded thru C203 M, and the 2000ppm signal to the ECU goes to C203 H. C203 H communicates with the ECU at connector 2, plug A10. Check the grounding of C203 M and all of the various connectors. Also check the integrity of the wiring terminals at the VSS plug.

Sounds good, I'll start checking. Thanks.

Let me know what you find.

quote Originally posted by olejoedad: Let me know what you find.

I didn't have a chance to look at any other wiring yet, but started at the VSS. The wiring looks pretty...crappy.



Here is the wiring at the VSS, unplugged to show how ragged the wires are:

Looks like a good place to start!

BTW - speedometer board often been found as the problem.....

Troubleshooting the Fiero Speedometer System by Oliver Scholz
http://www.fieros.de/en/articles/speedo.html

------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

quote Originally posted by Vintage-Nut: BTW - speedometer board often been found as the problem..... Troubleshooting the Fiero Speedometer System by Oliver Scholz http://www.fieros.de/en/articles/speedo.html

Based on reading the above, a failure on the board(s - the replacement did the same thing) could be the issue. I'll test everything. Thanks!