tachometer inconsistent and bouncing?

[imonna 19 6]

Hello all,

First two weeks of the season saw my boat head back to the mechanic for a new power pack, but since them its run wonderfully and my new tank, pumps, fill (and other assorted winter tasks) have been flawless.  

I did run across a minor issue and figure it is something others have run across.
  My tachometer sometimes doesnt work, sometimes works just fine.  Sometimes it bounces all over the place, sometimes it works fine.   Not rhyme or reason that i can find.

Where do i start troubleshooting.

Anyone have this prob before

PS the RPMS dont jump around, just the gauge.

Thanks in advance
Bill

[seabob4]

Bill,
On an OMC (Johnson/Evinrude), the tach has, for it to function, 3 leads.  Sender (gray), power (purple), and ground (black).  95%+ of all 12VDC issues are ground related.  That's where I would start...

[akbridge]

Your voltage regulator may be about to take a poo.  On my 90 OMC the tach worked unreliably for a while.  Then stopped all together.  A new voltage regulator and all was good again.

[fitz73222]

Check and see if your tach has a multi application selector switch in the back. Something like 9P, 12P, 4 cycle, etc. I had a tach do the same thing because there was an issue with selector switch. You should be 12P (pole) for most outboards. Push in on the switch selector and gently turn it back and forth an reset it to 12P. See if this works. I had a tach that I eventually had to replace because the selector would lose contact with the correct pole internally. It would work fine for a couple of months and then do it again. Also make all connections are clean as mentioned.

[GoneFission]

What year and brand of motor do you have?  Depending on the motor, retifiers and/or voltage regulators can cause tachs to act crazy.

[imonna 19 6]

1999 johnson 100
rectifier, stator, power pack just replaced.  The tack has been inconsistent since day one and the motot has been checked out and serviced 5-6 times for other problems.

I havent gotten under it yet to check the tach settings.

[jcaesar625]

I having the same issue on a Johnson 225 Ocean Pro. Stator checked out fine. I am thinking I have a bad ground. Hoping to have time between fishing this weekend to look into it.