I had some problems w/ my 92 Z/28, see here:
https://www.thirdgen.org/forums/elec...ied-again.html

Now that I have it back, I see that the rpm's on the tach are bouncing, maybe 200-500 rpms, about 1-3 times a minute. The rev's are NOT moving, just the gauge. No other gauge is having issues, and it didn't do this before the problems started. What is this? I'd prefer not to pay the dealership since it runs at least now, just not sure if this is still an engine problem that could leave me stranded.

Thanks!

 

It just dawned on me that when I was attempting to diagnose the problem, I saw that a wire was taped over connected to the coil. I don't remember the color, but now I'm thinking that someone back in time had a tach connected and then pulled it and put it back to "stock". I didn't like the look of the joint, so I pulled it off the car and used a butt connector. Maybe my connection is worse than what was there

I'm on a trip for work so I won't know until Thursday night, but I'm thinking that's it!

 

What you're looking for are the white wires on the coil.

Hope this helps.
Lou

 

Which one? It appears there are two, one that goes from the module to the coil, and one on the other side of the coil that goes into a plastic connector, then into the harness bundle.

The break in the wire I "repaired" was the white wire between the module and the coil.

I drove it to work today and it didn't seem to bounce, but it did last night when I took it out of the garage...

 

Both white wires are in the same circuit. Either of them can affect the tachometer or even the engine.

Hope it's working good now!
Lou

 

The car seems to not be quite as smooth as it was before this repair, but honestly, its got 140k on it so who knows. At least its driveable now! I'll pull that wire off and solder it that way its one less thing to worry about.

I will say that the volt gauge stays steady now, so I think the issues with magnetic field in the distributor may have been screwing up that as well.

Thanks!