Troubleshoot Yanmar 4JH2BE Tach

[sailguam]

Hi,,

I think the tach on my Yanmar J4H2BE is bad, but want to make sure before I order a new one.

With the engine running, I am seeing 12 volts on the Tach power leads (red/black stripe and black wires), but not seeing anything on the sensor leads (blue and orange). Note that I have the Tach unplugged from the harness, so if the sensor is just a switch that gets voltage from the TAch, I would not expect to see anything.

I tested the leads to the sensor (at the instrument panel) for continuity and saw an open, engine not running. Not sure if this means the sensor switch is open, the sensor is bad, or there is an open between the panel and the sensor. I tested for continuity on the orange and blue leads into the Tach and saw an open. I think this means the Tach is bad.

DOes the above indicate a bad tach? How should I troubleshoot the sensor?

Thanks,

Roger

[sailguam]

Humm,

I think I found the answer in the service manual. Just didn't look all the way the first time. Seems the sensor is magnetic and puts out a pulse. Sill not sure, but should I see a resistance measurement between the orange and blue leads to the tach? I guess I aso need to test the sensor at the sensor?

Thanks,

Roger

[Philsboat]

You might need an oscilliscope to see an output from the sensor.An electronics repair shop could test it for you if you gave them the wiring colour scheme.

Phil

[sailguam]

Thanks Phil, The sevice manual does say to use an oscilliscope. And we sure did not see any voltages with a multimeter. Problem is getting someone to take a scope down to the boat. Small island here an not many shops make dock calls. I might be able to borrow one.

[Chief Engineer]

Aren't the sending units for the tach sensing the gear teeth on the flywheel?

Take the sending unit out/clean it and re-install. Dirt or oil on the pickup can give you a faulty reading.

[Philsboat]

http://www.wellsmfgcorp.com/pdf/Counterpoint3_1.pdf

Hi Roger
Check out this site for troubleshooting Hall Effect sensors(these are used a lot for diesel engine tachs).might be some help.
Also you could clean the sensor and see if there is a red indicator l.e.d. that will pulse on and off as the target goes past it when the power is supplied to it

Phil

[Philsboat]

Principles of Operation: Variable Reluctance Sensors - Motion Sensors, Inc.

Here's another type of sensor.

Phil

[Philsboat]

Hi Roger
The orange and blue leads on the sensor should read 1.6 k ohms (1600 ohms) on the resistance scale (with no voltage applied to the sensor)and with 12 v. applied to the sensor the orange and blue should change from 0 volts to 1 volt as a gear tooth moves past it.
This is from my 1GM10 Yanmar manual.

good luck.

Phil

[S/V Antares]

With the engine running you should see some output from the 2 sensor wires with the meter set to AC (not DC). The sensors very rarely go bad but can. Make sure the wires go to the sensor on the bellhousing (Check color codes). I think someone mentioned that some newer Yanmars use Alternator output but I have not seen this.

[sailguam]

Hi Guys,

Thanks for all the help. I will eventually get it. I did test for resistance (at the instrument panel) and see an open. I guess I have to bend down int the engine compartment and actually get to the sensor itself (this weekend).

Yes Chief, the sensor is on the flywheel. And S/V Antares, my friend and I determined at lunch today that I should have been using the AC, not DC, setting on my multimeter. When I think about it, this should have been obvious, but getting a little senile I guess.

Big hep guys, but one more question if anyone knows. I checked for continuity, resistance, in the tach iteself, both on the power input (red/black) leads and the sensor (orange/blue) leads and both appear open. Shouldn't I see a resistance reading on one or both?

Thanks again guys.

[sailguam]

Let me clarify I tried to measure resistance of the sensor from the Instrument panel looking down the orange/black leads into the wiring harness. This weekend, I will actually get into the engine compartment, check and clean the sensor and measure reststance.

I am still thinking the tach may be bad since I see opens looking into the instrument itself. Guess that is why I wasn't paying as much attention to the sensor itself. Not to mention, it is a pain t get to in.

Thanks again