From a corvette forum,thought it might help.................That sounds familiar. Didn't happen on my Vette, but did on a GTP I owned, while driving through Louisville. At first I though I had been driving too long, or I was experiencing a brain aneurysm. However, when I got home to TN, I pulled up the wiring schematics, and the schematics for this particular vehicle displayed that only two things could cause this were the power feed to the HUD or the ground.
However, the HUD on a Vette receives all its information from the DIC; whereas on the GTP the signals are received directly from the displayed systems.
Damn, I should read the entire post before making these long answers. You did say your cluster display was also acting erratic.
If only your HUD speed and I/P Cluster speedometer were acting flaky go to the following steps. If your entire gage clusters including lights, oil, fuel, etc. were acting flaky go to the ground check.
- Check the vehicle speed sensor connector (Yellow and Purple wires), located on the Top RH side of the differential. (If you have an ohmmeter, you can check the resistance in these wires from the PCM to the sensor and have someone wiggle the wires and the sensor connector to see if there is any sign of an open circuit)
- Also check the Dark Green/White wire on terminal 50 (this is the speed signal from the PCM to the cluster).
From here on in, it gets pretty tricky. You will have to pull the cluster and check the connector and wires at the cluster connector.
It could also be the speed sensor itself is going out.
Now, if all the lights and gages were flaking out, I would assume a ground was at fault. However, if confined to just the speedometer and HUD, then it sounds like a bad wire, sensor, or even a DIC.)
Check the ground in the Instrument panel harness, that is located below the battery tray, on the RH frame rail. Make sure the ground is not rusted over, and is clean, and the connection if very tight.
If this is ok, check the wire at the terminal to make sure it is not broken on the terminal stud connector. If that is ok, you can check the splice pack, located in the Instrument panel harness, on the RH side of Instrument panel. This ground splice pack is connected to the ground mentioned above.
If you need any procedures or further information, write me at whitec5vette@aol.com.
