Sticky Tachy

[dehler25]

The original Yanmar tach is behaving badly! It seems that the needle movement has become stubborn at times. It often does not return to zero on shutdown and reads incorrectly, sometimes it operates as if no problem. The unit is sealed as a side mounted pod so I would prefer to resuscitate the original rather than transitioning to a digital. I doubt this is the only tach that has developed an attitude. Anyone got a fix?

 

[markwbird]

new tach

 

[JohnVTX]

Connections.

 

[Ralph Johnstone]

See reply #9.
A cheap solution as electronic tachs are not easily repaired once the unit has failed.

http://forums.sailboatowners.com/index.php?threads/could-it-be-the-tach-sensor.138629/&highlight=heart monitor

 

[sailcapt340]

Try checking the sensor located on the top of the transmission bell housing.
It is a large nut with 2 wires on the top. You can remove the wires and clean the contacts with steel wool or emery cloth, clean both the contacts and the inside of the wire clips. Corrosion is usually the cause of erratic readings. Each time the
magnetic pickup sensor on the flywheel passes the sensor it reads it as RPM. Check for loose terminals also.
You can check the voltage on the wires on the back of the gauge - black is ground, red/black is 12v.
At the sender - should be 1.6 +/-0.1 KOhms.
I've include pictures of mine (2000 340 - Yanmar 3GM30F). Mine was the corrosion the voltage was just as above.
If it turns out to be the unit itself, it can be replaced for around $130 - $150
Hope this helps.

 

[dehler25]

Thanks I have something else to now chase! The older thread was a great help.

 

[dehler25]

It appears that the connections on the sending unit were foul! I thought it sourced its count from the front of the engine and not from the flywheel. Cleaned and reseated the connections under the turbo and it is working as advertised. Great info fast!