93 Tach reading high

[captaudi]

Afternoon,

This afternoon on the way home from work my tach got all funky on me, and not in a good way. Its reading almost exactly double. Normally around town in traffic I shift approx 4k rpm. Today it was showing more like 8k. As soon as I got home I grabbed my fluke and checked system voltage. 12.74V at idle 14.2V at about 3k rpm.

I looked in the archives and this does not appear to be a common issue. There was one post where FJ4ever adjusted a pot on the back side of his tach fixing his issue. My feeling is in a perfect world that should not need to be adjusted.

Anyone seen this and what did you find?

Thanks,

[mbagger79]

Hi there.

Just chipping in... Wondering if you had a solution to your problem, as I have what seems to be the exact same problem on my '93 FJ1200A (abs).

To add; to me it does not happend on every ride. When it happends, and I continue riding, after around 30 minutes or so, it starts slowly dropping back to normal RPM's on the gauge; finally setteling with the correct readout.
Mostly the problem occours after some time riding. Once, it happended directly after startup, and reving it a bit.

[red]

In either case, my first idea would be dirty grounds to the instrument panel. There are several ground connections on the panel.  Dull metal is corroded metal.  You want all electrical connections to be made with bright, shiny metal.  Adding a dedicated ground wire near the tach won't hurt, and might help.  All IMHO, of course.

[captaudi]

I have not sorted this out yet, I performed a voltage drop on the 12V feed and the ground to the instrument cluster. Both around 0.2V, not horrible. It is very inconsistent, last week it was almost everyday. This week, not once. I also checked the trigger to the coils when it was acting up, identical on both. Being as the tach gets it signal from one coil and not from the CDI box I don't think a coil is double firing. Waiting for a Saturday when it acts up and I have the time to pull the upper fairing to access the back of the cluster.