Yanmar Tachometer

[alofns]

We have Yanmar 3YM30. When we start the engine, the RPM Guage reads 0, but the needle moves as we power it up, so we know it is making a connection.

Any suggestions on what might be going on?

[chris mac]

I'll try to help, but keep in mind my only knowledge comes from working on my own 3gm30f. So this info may be of no help.
The leads for the tach come from the sender just above and in from the starter. I beleive it works off of the flywheel. I'll try to attach a pic. The arrow is pointing to the sender. These connections do get loose frequently.
The other problem I've had came from the ground. If the ground wire is loose, it could cause this intermittent functioning. So check that connection as well.
Usually something like this will come down to a corroded or loose connection.
Good luck

[bstreep]

Most Yanmar electrical problems are grounding problems. They undersize ALL of their wires, but the grounds seem to be particularly troublesome.

[SV-Viento]

Originally Posted by bstreep

Most Yanmar electrical problems are grounding problems. They undersize ALL of their wires, but the grounds seem to be particularly troublesome.

On this same line of thought trace and clean all related electrical connections. We had similar problems and it was a random corroded connection.

Btw we had the same engine- loved it

[skipperpete]

Originally Posted by alofns

We have Yanmar 3YM30. When we start the engine, the RPM Guage reads 0, but the needle moves as we power it up, so we know it is making a connection.



Any suggestions on what might be going on?

Definitely check all the harness plugs and connections first and then check the alternator, your tachometer gets its input from the AC terminal and according to the wiring diagram there’s also an external diode that might need checking. I think if the belt was slipping badly enough to cause the tachometer to not register you would also be seeing a bit of engine overheating.... but check the belt tension.
I’m assuming you have the original 3YM alternator and int reg.

[markxengineerin]

If you get tired of debugging the Yanmar system, you can add a TinyTach. I used one for a while before fixing my Yanmar (replaced ground and sending unit, both of which were very corroded). The tinytach was small enough to fit right on top of the yanmar dial with temporary velcro.

[Tin Tin]

This assumes you have standard Yanmar 3YM30 alternator and a Yanmar B Panel set up.



You can do a couple of tests to see if it is the tachometer or the sender/wiring.
1. Use a voltmeter on AC to test the yellow/orange pulse wire coming out of the alternator, there is a connector there. Ground meter to negative on engine or battery It will read a low voltage, as you speed up the engine the volts will change (Our read around 7 - 8 V AC). Clean connector with emery paper whilst you are at it.
2. Next test the back of the tachometer, pull the plug out of the back, stick the AC probe into the orange wire connection and the negative into a ground or the black wire that goes into same plug. It should read around the same volts, if not you have a dud wire connection somewhere.
3. To double check run a separate wire from the alternator tach sensor connection all the way to the tachometer and with the plug in, touch wire to the orange wire connector, if tach responds it confirms that the tach works, small alligator clips are useful for this exercise.

4. Trace the orange wire from the alternator all the way through its path to the instrument panel. You may find that where the electrical harness to the engine is joined amongst a whole bunch of wires and joiners, these are subject to corrosion over time and often the wires need to be cut and rejoined as the corrosion has crept up a few inches into the wire core especially if un-tinned copper wire has been used.

[GordMay]

Originally Posted by Tin Tin

This assumes you have standard Yanmar 3YM30 alternator and a Yanmar B Panel set up...

Yanmar “B” Type Panel Wiring Diagram
➥ https://www.cruisersforum.com/galler...&cutoffdate=-1


Magnetic Proximity Sender on Flywheel
➥ https://www.cruisersforum.com/galler...r&imageuser=79

[Tin Tin]

This is the one I use

[OldManMirage]

It might just be a calibration issue.

Get a tachometer app for your phone and then look at the back of the tach - there should be an adjustment screw. Try tweaking that and if you get more reasonable readings try calibrating it with the tach app.

[skipperpete]

Originally Posted by GordMay

Yanmar “B” Type Panel Wiring Diagram
➥ https://www.cruisersforum.com/galler...&cutoffdate=-1


Magnetic Proximity Sender on Flywheel
➥ https://www.cruisersforum.com/galler...r&imageuser=79

Thanks for the wiring diagram gordmay, every day brings a new morsel of knowledge, I’ve never seen a 3YM with a tach sender.

[GordMay]

Originally Posted by skipperpete

Thanks for the wiring diagram gordmay, every day brings a new morsel of knowledge, I’ve never seen a 3YM with a tach sender.

Tin Tin's diagram is clearer.
https://www.cruisersforum.com/forums...ml#post3791565

[RaymondR]

See the notation mid right where it says "1.2 acv MAXIMUM at idle".

Suggests you should set your multimeter to AV volts and observe whether there is 1.2 volts. If so the problem is probably in the wiring.

I think those things are referred to as " magnetic reluctance transducers" there's a little magnet with a coil of wire around it inside and the steel teeth passing through the magnetic field cause it to vary inducing an ac current in the coil.

Built one once and used a Schmidt trigger feeding an LM2907 to process the signal and a moving coil meter for readout. Calibrated it using a 4000 series decade counter and flashing LEDs I timed with a stop watch.

[skipperpete]

Thanks for the excellent post TinTin, that makes things much clearer.

[etoimene]

Thanks for the schematics!

My Type B display just shows message "SELECT" on display and tacho is not working.

Any ideas?
I still have to take multimeter with me to the boat to check for the usual suspects.