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Old 15-03-2013, 16:17   #1
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Yanmar Tachometer Problem

I have a Yanmar 4JH4TE on a sailboat, and the tachometer is reading really high; approximately 4000 RPM when it is actually running at 2800 RPM. I would appreciate any suggestions as the cause.

Thanks
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Old 15-03-2013, 16:23   #2
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Re: Yanmar Tachometer Problem

I have had problems with my tach on both of my Yanmar equipped boats. One was a bad connection in the wiring harness and 1 was the tach itself.

Both times those resulted in the tach reading low or not reading at all.

The only thing I feel could cause it to read high is the tach meter itself is bad. But I would check all the connections at the tach, harness, and on the bad of the tach first.
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Old 15-03-2013, 17:05   #3
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My yanmar tach doesn't work at all. I've cleaned the pickup on the engine. Not sure what else to do before buying a new one, which I really don't wanna do.
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Old 15-03-2013, 17:10   #4
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Re: Yanmar Tachometer Problem

check the wire with a multimeter.
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Old 15-03-2013, 17:43   #5
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Re: Yanmar Tachometer Problem

Engine running, pulses come from either a pickup or the alternator, are converted to an analog signal, and fed to a meter. That's the standard analog tach in a nutshell.

It's fairly easy to check the wires, connections. It's a bit harder to check the pulse output, but some digital meters have a frequency setting. Best is a portable oscilloscope, but who has one of those? (Ok, me) If the wires and signals are Ok... then it's got to be a problem with the tach meter or circuitry.

Yes the factory tachs are expensive. One option is to get a generic replacement tach.
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Old 15-03-2013, 18:13   #6
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Re: Yanmar Tachometer Problem

I don't feel it possible for ANY failure of the flywheel sensor on a Yanmar 4JH, or any wiring failure to make the tach read high.

Like I said I would check the connections just because. But in end my money is on the meter itself being bad.
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Old 15-03-2013, 18:47   #7
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Re: Yanmar Tachometer Problem

If it's an alternator run tach, the alternator itself maybe going bad. If a diode in the rectifier is shorting out it could send out a bad pulse. Or the brushes could be bouncing from being too short.

How old is the alt?
Check your voltage to the batteries.
A low reading could be a slipping belt.

But with the reading too high I suspect the tach is the problem.

Tach Calibration>>>> Tachometer Calibration
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Old 15-03-2013, 20:28   #8
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Re: Yanmar Tachometer Problem

My Yanmar tachometer was running fast as well. I bought a $28 tachometer off the Internet and took the "do not remove" label off the back of the boat tachometer and recalibrated it. When I bought the boat new it had a 60 amp alternator, but they replaced it with an 80 amp which it should have had. I figured the 80 amp gives a different signal. The boat is a knot and a half faster now.
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Old 15-03-2013, 20:41   #9
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Re: Yanmar Tachometer Problem

I have the the 4JH3 and the same problem once in a while.

Clean the connections, if that does work... Play with the adjustment crew onthe back that says don't touch and has a bit of wax on it.
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Old 22-06-2013, 06:48   #10
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Re: Yanmar Tachometer Problem

there is a technical bulletin MSB 03-015 by Yanmar tell you how to set the tachmeter . for 4JH4TE, you have to set the pulse / rev in the meter at 10.29/rev. The procedure : there is a small opening at the low sided at the back of the meter covered by a paper label. use a wooden stick to press the tiny button inside , hold it and turn on the switch. you will hear the alarm and in the LED panel , you see the alternating ADJUST or PULSE in the display panel every 2 second . when the PULSE shows up, release the button, something like P 14.50 appears , The last digit will flashes, Then you have to change this digital to 10.29. begin by pushing the button by the wooden stick to change the flashing digit. Stop pushing the button once the pulse count is correct. Like P 10.29. the setting is completed .
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Old 22-06-2013, 06:57   #11
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Re: Yanmar Tachometer Problem

Sorry , the above calibration is for the Digital B-type panel made by VDO
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