Goofy tachs

[bogus]

First question on the forum, hope you guys have the answer! New to us '95 330 Sundancer w/V-drives behind Bluewater 454's.

I've noticed this the last couple of times out for a cruise on the Mississippi. When we get to the channel, I'll put the rpm's at about 1300 for "puttsing" mode. After a few minutes, I notice that the port tach is wandering and holding around 2000-2100 rpm's. The sync gauge does not agree with this. It says the engines are synced. My ear tells me the same thing. If I stop and put the trans in neutral, the port tach says the engine is idling at about 1100rpm, but again the sync gauge and my ear don't agree with this. The starboard tach acted the same way on the next trip. Actually they both acted up on that trip.

Now the wierd thing is, that if I come to a stop, and shut down the engines for a couple of minutes and re-start, the tachs will behave for the rest of the trip, so I have kind of ruled out a bad connection. But if I were check for a bad connection, where would I look?

Has anyone had this kind of thing happen, or am I "unique"?

 

[Presentation]

Remove the tach. Turn it around. Take a little screwdriver and look for a switch. Flip that switch back and forth about a dozen times. Put it back to its original location. Reinstall tach.
The same tach is used for 4, 6 and 8 cylinder engines. The switch is for this setting. The contacts get some corrosion on them and they go goofy as you describe. By switching them back and forth you rub that corrosion off. It should last for a few years then you repeat.

 

[Air O'Nautical]

Remove the tach. Turn it around. Take a little screwdriver and look for a switch. Flip that switch back and forth about a dozen times. Put it back to its original location. Reinstall tach.
The same tach is used for 4, 6 and 8 cylinder engines. The switch is for this setting. The contacts get some corrosion on them and they go goofy as you describe. By switching them back and forth you rub that corrosion off. It should last for a few years then you repeat.

Thats is the trick...........common problem.
Also, try to dry them out. Put a small electric heater blowing up behind the instruments for a while. Worked for me anyway.

 

[bogus]

Thanks guys, I will give that a try although it will ba a while since I am working 9 straight 12 hour days through Memorial Day weekend! (4 of them time and a half, and one double time. Helps pay for the "new" boat!) Will let you know if it works.