Flakey Tach

Mightychan

Member
Oct 8, 2016
157
Panama City FL
Boat Info
2005 DA 420, AB Dink
Engines
Cummins 6CTA
I just sea trialed an 05 DA 420. The port tach was not working properly...it's readings would wander, and if you tapped it hard, it would settle down, then start to wander again. Engine ran perfectly. The owner says his marina recommended replacing the tach, but waiting until the boat sold, since the hour meter is in the tach, and the new tach would show zero hours and look suspicious. I just can't believe that 1) the tach would not be repairable, and 2) a new tach would not have a way to set the hours to match the one it replaced. Advice, please? My preference, of course, is to repair the existing tach. What should I look for?
Thanks
 
Tachs are known to have issues so don’t be suspect.

They are available on flounder pounder.

Yes it is most likely the tach and not the sending unit.

The hours cannot be programmed.

Josh
 
The tach on my 98 does the same.

I consider it a feature. ;)

But seriously I'm going to take the dash apart at some point and clean the connections and put a little electo grease on them to see if that helps.
 
Cleaning the connections won’t do a thing. The tach must be replaced.
 
I just sea trialed an 05 DA 420. The port tach was not working properly...it's readings would wander, and if you tapped it hard, it would settle down, then start to wander again. Engine ran perfectly. The owner says his marina recommended replacing the tach, but waiting until the boat sold, since the hour meter is in the tach, and the new tach would show zero hours and look suspicious. I just can't believe that 1) the tach would not be repairable, and 2) a new tach would not have a way to set the hours to match the one it replaced. Advice, please? My preference, of course, is to repair the existing tach. What should I look for?
Thanks

Did you have readings taken directly during the engine survey/sea trial? That's a must to establish performance versus the power curve, rather than relying on the gauges. If not then have that done. Whoever did your sea trial should have recommended once the tach was shown to be flakey.
 
There was a solution to the tach needles floating on a previous thread..remove the tach from the dash and cycle the settings on the back of the tach (take note of the original position). I assume it’s an analogue gauge since you mention tapping it settles down the tach for a while.

http://clubsearay.com/index.php?threads/replace-tach-gauge.54202/
 
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I had this same problem, in my case turning the switch that picks either 4-6-8 cylinders back and forth a few times fixed the connection problem, which was the source of bouncing readings.
 
I had the same issue. Swapped to the Aetna tach and never looked back. I wrote the hours on the old tach directly onto my engines. If I need the total time I just add.
 
Those hours are in the ecm, which gives the data to the tach... so replacing won’t zero out the hours .
 

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