Within the last month or so, I've been seeing some weird behavior from my tach...

Sometimes, it works fine, but that's been becoming pretty rare...

Sometimes, it will read somewhere between 1/3 and 1/2 of what it should read. When it's doing this, it will definitely stay at that exact-but-undetermined fraction of the real RPM's. It doesn't seem to vary while it's happening, but it DOES seem to vary from one driving session to the next.

This morning, however, the needle barely moved...at idle, the needle was resting on the peg, and at approximately 2500rpm, the needle barely raised off the peg about 1/8". This afternoon, though, the tach seemed to be working fine.

Any thoughts? Does this indicate a problem with the tach itself, or should I be looking elsewhere? There's no other apparent problems.

Electrical Grimlin <img src="/forums/images/graemlins/rodent.gif" alt="" /> I say bad tach or loose wire.

<img src="/forums/images/graemlins/cheers.gif" alt="" />

I've seen a bad coil wire cause this many times, but it could also be the tach itself. As you have some movement, I would not think that there is a connection problem. If you pull the panel behind the cluster, in the round wiring connector that goes to the cluster itself, there will be a white or a white/blue wire that sits in the #12 position in the plug.(I think that one 1 side of the wiring connector it is blank, and on the other side the wire is red) You could check the signal there with a remote tach to confirm its pressence. I remember it as I needed to add a signal conditioner when I added my MSD, and I did it under the dash/cluster, rather then in the engine compartment.
Kary

Also clean the contacts and check continuity from the other end of the blue/white wire at the coil - terminal to that dash panel connector. I have a couple of used instrument clusters if you need one. Is your power output fine, just a wonky tach?