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Old 09-11-2011, 05:56   #1
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Yanmar Tachometer Bouncing . . . Replacement ?

Greetings oh wise ones!

For a while now my tachometer has been somewhat jittery.. Meaning that it shows the correct speed then suddenly dips.. Then goes back.. Then dips again.

Recently its been sitting at zero and sometimes showing the right rpm, the. Zero.. Dip.. Etc etc

I thought it might be corroded terminals, so have cleaned the terminals on the sensor... No joy. I then removed and crimped on new connectors.. Still no joy.

So I'm begining to think the tacho itself is faulty.

Two questions:

1. Is there any way to troubleshoot the tacho itself?

2. Assuming that its faulty, is there a drop in non-Yanmar replacement anybody knows of? (yanmar one in Australia will be minimum $500)

Thank you!
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Old 09-11-2011, 06:26   #2
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Re: Yanmar tachometer bouncing.. Replacement?

Before you tear into the tach, the symptoms are an exact match for what happens if you have an external votage regulator installed and have fully charged the batteries. Some of the regulators go to zero alternator output, which shuts off the tach.

This is easily tested by turning on a relatively high current D.C. load when the tach is bouncing or registering zero. If the tach works normally with the load on, then you don't really have a problem -- just a nuisance. There are a number of ways around this; most center on adjusting the regulator. That depends on the regulator, of course.

I just live with it; I know the batteries are full when I'm cruising and the tach shuts off. If I need the tach for some reason, I turn on a few lights.
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Old 09-11-2011, 06:27   #3
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Re: Yanmar tachometer bouncing.. Replacement?

What Yanmar engine do you have. Where's the sensor, on the Alternator or?
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Old 09-11-2011, 08:13   #4
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Re: Yanmar tachometer bouncing.. Replacement?

My sensor is on the flywheel, and it was a corroded connection, Small piece of sand paper, and problem fixed.......i2f
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Old 09-11-2011, 08:34   #5
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Re: Yanmar tachometer bouncing.. Replacement?

Quote:
Originally Posted by imagine2frolic View Post
My sensor is on the flywheel, and it was a corroded connection, Small piece of sand paper, and problem fixed.......i2f
Indeed.
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Old 09-11-2011, 08:45   #6
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Re: Yanmar tachometer bouncing.. Replacement?

Make sure the lead from the ignition switch has a constant source of current.
A dodgy switch wouldn't affect engine operation, but could cause your problem.
A squirt of WD 40 or similar into the contact area couldn't hurt.
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Old 09-11-2011, 11:36   #7
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

Thank you for your replies.

I feel pretty silly now, I should have stated the engine type! It is a 3GM30.

As for alternator output etc - the sensor is on the flywheel, so is independent of alternator output and battery state.

I also tried the sandpaper on the corroded terminals, but no joy there.

There are definitely no loose connections, I double checked everything, so I'm quite sure its not that.

Any other thoughts?
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Old 09-11-2011, 11:53   #8
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

When the tachometer (Ign. Sw.) is first turned on, pointer must go to between zero to 50 RPM. If not, check connections (if OK, tachometer is probably faulty).

Voltages, with engine running should be:
IGN to GND terminal: 12-16 VDC
SEND to GND terminal: 0.3 VAC to 1.2 VAC minimum at idle; (voltage will increase with engine speed)

The end of the (magnetic pick-up) sender must be within 1/32" -1/16" of the (flywheel) gear teeth, but not touching the teeth. To adjust, stop engine, loosen the lock nut, and gently turn the sender clockwise until it touches the flywheel. Back off (counterclockwise) one turn, and secure with the locknut.

Rust buildup between the flywheel teeth can cause signal loss from the sender.

See also ➥ http://www.marineengine.com/products...Tachometer.pdf

Yanmar instrument panels may not have used Teleflex instruments, but the principles will be the same.
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Old 09-11-2011, 11:55   #9
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

Check the wiring harness again. I had the same problem 3GM30F and it was a bad connection in the harness.
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Old 09-11-2011, 11:59   #10
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

Quote:
Originally Posted by Vasco View Post
Check the wiring harness again. I had the same problem GM30F and it was a bad connection in the harness.
A bad connection will cause arcing/resistance which will just get worse.
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Old 09-11-2011, 12:51   #11
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

Quote:
Originally Posted by GordMay View Post
When the tachometer (Ign. Sw.) is first turned on, pointer must go to between zero to 50 RPM. If not, check connections (if OK, tachometer is probably faulty).

Voltages, with engine running should be:
IGN to GND terminal: 12-16 VDC
SEND to GND terminal: 0.3 VAC to 1.2 VAC minimum at idle; (voltage will increase with engine speed)

The end of the (magnetic pick-up) sender must be within 1/32" -1/16" of the (flywheel) gear teeth, but not touching the teeth. To adjust, stop engine, loosen the lock nut, and gently turn the sender clockwise until it touches the flywheel. Back off (counterclockwise) one turn, and secure with the locknut.

Rust buildup between the flywheel teeth can cause signal loss from the sender.

See also ➥ http://www.marineengine.com/products...Tachometer.pdf

Yanmar instrument panels may not have used Teleflex instruments, but the principles will be the same.
Thanks for this - when you say that the pointer must go to 0-50, are we assuming here that it sits below 0 when ignition is off? (I can't remember exactly, but I think there's a hard stop on the the Yanmar tacho exactly at zero and turning ignition on has no effect).

I will look at these today though when I get to the boat.
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Old 09-11-2011, 12:52   #12
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

Quote:
Originally Posted by Vasco View Post
Check the wiring harness again. I had the same problem 3GM30F and it was a bad connection in the harness.
So how did you resolve it? Just re-run the sender wires or replace the lot?
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Old 09-11-2011, 13:00   #13
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

I have the same problem currently on my boat, and had it last year on my last one.

On the last 1 it was the connection at the wiring harness and I had to install a jumper around the connector. haven't looked for the problem my current boat as it doesn't really matter all that much as I can tell by sound and speed what the rpms roughly are.
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Old 10-11-2011, 12:10   #14
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

Ok, an update... I checked with a multimeter first and the results were inconclusive.

The Yanmar service manual shows that there are SIX wires going to the tacho(inc illumination), but in reality, there are only 5! I checked with another owner and it appears that the manual is WRONG!!!

The manual also shows that both legs of the sender go to the tacho. However, they dont. Only one leg goes there. The other disappears somewhere in the harness.

Using a multimeter set to AC, when the engine is running, there is a reading of approx 11 VAC betweeen the legs of the sender. Voltage increases with RPM. It appears that the sender generates its own voltage, since there is no other input to it (magnet + coils???)

In short, i planned to cut the wires in the harness back until I found fresh copper - but it was all black. So I crimped up a new pair of wires to the legs of the sender. As I mentioned, the service manual diagram is wrong, so I experimented and found that if I ground one of the legs of the sender and take the other leg to the tacho, it works.

My question now, is WHY? Why would they have two leads if one is supposed to be grounded when they could just ground the sender to the engine itself through the sender body and just have a single lead? Despite it working now I am afraid that I am doing something wrong by grounding what is effectively half of an AC circuit to DC ground.

Thoughts?
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Old 10-11-2011, 18:46   #15
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Re: Yanmar Tachometer Bouncing . . . Replacement ?

One side is suppose to go to ground and the other to the tach. The tach has a power input and output to the sender. It is a reed switch that is magnetic and counts the teeth on the fly wheel, which sends the number of teeth to the tach computer and actuating the needle.


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