Yanmar tachometer

[Texas johnny v]

I have a 2008 Hunter 38 with a Yanmar 3jh4e with about 100 hours on it. Over the last several weeks the tachometer has been working intermittently. Sometimes on start up it remains at 0 RPMs. After a few minutes it will kick in and begin reading RPMs properly. The tach also works well for a while, reading RPMs properly and then drops back to 0.

As far as I can tell, the tach is reading off the alternator, not the bell housing of the engine. I have manually checked the wiring from the back of the instrument panel to the alternator. All looks tight with no chafing.

Any ideas about what to look for/do next.

Thanks,

John

 

[dmc1]

alternator tach

A alternator tach sensor is a magnet passing a metal object that counts revolution. Check the sensor alignment. Is the belt tighter or looser than before, or something that could be distorting the sensor.

good luck

Peace

dmc

 

[Larry Jackel]

Could depend on state of battery charge

My 2005 H44 came with a smart voltage regulator so that when the battery is fully charged the alternator is shut down. This caused the tach to read zero. The fix was to abandon tach sensing from the alternator and install a standard magnetic pickup on the flywheel.

 

[Vinny]

Sometimes on start up it remains at 0 RPMs. After a few minutes it will kick in and begin reading RPMs properly. The tach also works well for a while, reading RPMs properly and then drops back to 0. John

John,

As stated by Larry your tach picks up impulses from the alt. If you have an external smart regulator it could be acting like Larry said but even when the batteries are at full charge the alt is putting out at least 12.3V or so as a float. But if you do not have a smart external regulator the internal regulator may be giving you some trouble. Some time they won't start to charge until the RPMs get to a certain number, thus no reading.

Also do check the belt to be sure it isn't slipping. Make sure the alt is grounded to the engine properly and that the ground wire hasn't corroded. Check the wire for the tach that goes to the alt for corrosion as well.

 

[Bill Roosa]

Things to check

If it is picking up impulses from the alternator then you should be able to get it to start reading by turning on something that draws a lot of current.
Also check all the connections between unit and the alternator. Corrosion happens here just like in the starter control circuit.

 

[Marc14857]

Larry

Did you do this modification and if so can you provide details. I may be having tach problems on my 2005 H44 in that it is reading low and I never get the speed the other H44 owners get while under power. I purchased a photo tach and hope to verify that this is the case at which point I will want to install a new sensor on the flywheel as you did.

Thanks
Marc

 

[Larry Jackel]

Marc,

My boat has a Link 2000R voltage regulator and that seems to have been part of the tach sensing issue. The dealer did the fix, but I believe it is quite straightforward. Mack Boring (Yanmar rep) can probably supply parts (mag pickup) and advice (wiring info). If I recall your problem, your boat never gets to 7kts when you push it to full throttle regardless of the tach reading, so I suspect your problem lies elsewhere.

 

[Marc14857]

Larry

I am going to update my post on the speed issue. I purchased a hand held tach and this weekend found out that the engine tach reads about 900 RPM low at 3000 RPM. Apparently I was reluctant to advance the throttle beyond 3000 RPM but finally did. My installed tach reads about 3900 RPM and my hand held tach is at 3000 so the prop issue is solved. I have the upgraded Balmar 90 - 100 amp alternator with the smart regulator. I also feel a whole lot better about the prop and the engine.

Thanks

 

[Vinny]

You might check the back of the tach. Some have an adjustment screw and you might just be able to recalibrate it.