2006 F115- Yamaha tach jumping around

[herb.wilson@uno.edu]

I have a yamaha digital tach hooked to the engine. It will jump around in values while running. I also have a NMEA 2000 network attached to the engine as well as a NMEA 2000 compatible gauge and the RPM reading from that gauge reads steady numbers while the yam digital tach is jumping around. I know the tach jumping around can be a sign of a regulator/rectifer going bad. It can also be a bad electrical connection to the tach. Just wondering if the regulator/rectifer was going out, would the erratic RPM readings be reflected in the NMEA attached gauge as well. I would imagine so but I want to confirm. The digital tach is old and I can do without it but I want to make sure the regulator/rectifer is OK.

[herb.wilson@uno.edu]

Any ideas?

[CatCam]

Okay - if you have a Yamaha Multifunction Speedo check your Voltage reading.....if it is rading 16.4V - 16.6V your regulator is going bad....Just had mine burn up on me a few months back.....

But long before this happened my tach stopped working - just would read "0" RPM with the engine running. I figured my CDI was to blame so I got on the forum here and learned a trick. You can run your digital tach straight from the Voltage Regulator - It has 5 wires:
2 green, 1 green/white, 1 black, 1 red
I jumped directly from one of the green wires to the green wire of the Tach...my first guess was wrong, I then jumped off the other green wire and the tach worked perfectly. The CDI is just a throughput for your tach.

BTW - we did find out why the tach stopped working. About 2 years ago I took my carbs off to clean them, when I put them back on I pinched the wire to my Prime Start Selinoid - this caused a bunch of problems with my idle AND gave faulty info to my CDI causing the tach not to work. My Yamaha tech said that the pinched wire ultimately caused my Regulator to go out as it caused grounding issues.

University of New Orleans????

[herb.wilson@uno.edu]

The NMEA gauge can display "alternator" voltage and it displays around 14.3V consistently while running. Does not appear to be a faulty or failing reg/rect. I bet that old tach is going bad or wiring to it is suspect.

Yes, University of New Orleans.

Thanks for then reply and info.

[herb.wilson@uno.edu]

Update

Went out today and the tach acted the same, even went to zero and stayed there at high rpm's. Teh tach is old and my just be going bad. I noticed the "alternator voltage" displayed on another gauge was jumping around 13.0-13.9 by tenths increments up and down. Early in trip it was reading up to 14.2. The rectifier seemed failry hot to the touch also. Is that normal for the rectifier to get that hot. Batteries are both good and they do seem to be getting charged. The alternator voltage readings acted the same with both batteries. Any more ideas.