Can a OEM tach become bad?

[ColeTrickle]

I have a '83 that has a OEM tach needle that bounces between 500 and 1000 rpms. I guess its in the ballpark but this is unacceptable.

I thought I found a helpful search page only to later see it was for an ebayer trying to sell his used CJ7 tach...saying "they don't last forever".

So with my given explaination, think mine is bad?

thank you for any and all advice.

 

[Torxhead]

A comparison with another tach of some sort would help to verify if you have an issue.

 

[TeamRush]

The big question is,
Is the engine running smoothly?

Jeep used a SERIES, or CURRENT SENSING tach, meaning it reads TRIGGERS from the ignition coil,
If the engine IS RUNNING SMOOTHLY, it's the tach.

If the engine has Misfires, the tach is probably correct and the ignition system needs some help.

Tachs do fail, and when a Series tach fails, it often keeps the engine from running.
Since the IGNITION POWER goes through the tach, then on to the ignition system,
When the tach fails, the ignition fails in some cases...
(Depending on what failed in the tach)

If you stick your head under the dash, you will find the factory tach has two leads, and a light wire going to it.

The two leads have connectors that will plug into each other, excluding the tach,
(For vehicles ordered without tachs)

If you have misfire issues,
Simply unplug the tach, plug the HARNESS wires into each other and see if the misfire or ignition issues go away.
This is the most simple way to test for tach issues in the ignition system.

 

[Lumpy Grits]

There's a small spring inside the tach that dampens the needle's movement.
Those springs do fail sometimes, and that can give you the 'bounce' you now see.
LG

 

[ColeTrickle]

There's a small spring inside the tach that dampens the needle's movement.
Those springs do fail sometimes, and that can give you the 'bounce' you now see.
LG

That's it! It doesn't bounce as I first posted. I did have some issues with timing so it was bouncing rapidly.

All is well. Thanks to all who replied.