Intermittant tacho operation

[Mybigblue]

The tacho on our C320 with a Yanmar 3ym30 works intermitantly. I have replaced the tacho and the problem persists. It will start and stop at will. Operating a electrical item such as bilge blower or fresh water pump etc will get it going if it is in the non working state. Have checked all the connections behind the gauge pannel. I thought it could be a earth issue??? Would anybody like to have a stab at solving this one this one and make a friend for life.

Regards Al.

 

[Stu Jackson]

The tachometer works off the alternator. Either your batteries are fully charged when this happens so the regulator is satisfied and is not directing the alternator to "put out" (probably keep your boat plugged in all week, right?) OR you have a loose wire on the back of the alternator, or both.

C32? C320...

And "tacho" is a new one on me.

 

[larryw]

What Stu said; if you have a "smart" regulator, and the batts are fully charged, the regulator turns off the alternator, that's why turning something on will activate it. The tach will also stop working for a few minutes when the regulator changes charge states, from accept to float, but the tach will come back. At least, that's how it is on my boat.

 

[ITMaster]

I also found

in my 387 at the rear of the engine compartment where the wiring harness runs back to the pedstal a spot where the bundle of the wiring harness connected to another bundle. There was a spot where the bundle had tension on it and the wires were intermittantly being connected and disconnected. A slight adjustment took care of the problem for me and it hasn't been back since.
But the harness may not be on the C32 like it is on the 387, however if you can't find the problem, this may be something else to check. Good Luck

 

[Bill Roosa]

Not all tachs run off the alternator!!!

With all due respect to Stu, three of my boats did not have the tach run off the alternator!
You have a classic "connector" problem. Your comment of "turning on other things makes it come alive" clearly indicates that you have a ground problem as that is the only thing they share.
Tachs that do not run off the alternator have a "sender" that produces AC current pulses. Tachs that do run off the alternator use the AC current from it as their input. In either case the tach proper needs a good chassis ground to make sense of these.
Since you can get the unit to respond by turning on other electrical equipment check what wiring they have in common.

The Great Roosack predicts that you will find a "non-signal" chassis ground that is corroded.

 

[Stu Jackson]

Good point

Thanks, Bill, for noting that.

Al, one of the things that the moderators of this board have suggested is that questioners provide a bit background of their boats. In your case, the engine type and alternator type would have helped a lot.

If you tell us that information, we can help more specifically.

Not to be a nit picker (yeah, right) but do you have a C320, because I never heard of a Catalina 32?

I'm guessing a Yanmar engine.

 

[sailaway78]

Some Yanmars

Some Yanmars run off of a sensor which is mounted on the flywheel. I would think like others that you have a ground problem, but first check out the two plugs on the Yanmar harness. They sould be located pretty close to the starter solenoid. These can become a little loose, or, heaven forbid, get bumped doing some other project, causing a weak or intermittent connection.
Thats just a quickie check, but I would still look for a bad connection somewhere, and would look at the grounds first.

 

[Stu Jackson]

Also occurs to me that even if it was a Yanmar engine, Catalina may have chosen to use the alternotr to the tach. We just don't know, but Al oughta look into what he has a little bit more. Good luck, Al, please let us know what's goin' down.

 

[Rich (P303)]

I guess we need more information...

I have a Yanmar 2gm (1984 vintage... ran off flywheel) and my tach would run intermitantly... or slowly get up to speed and then back down after the engine was off. My problem was the tach... replaced... fixed. (after the yard put in the wrong tach, sender... and said it was I wiring problem) That bill wasn't paid!

I would check the sensor connection around the flywheel (if you have one)... that item is $100+ if I recall.

It seems to me this will be a two man operation. Someone watching the tach with the beverage of choice... the other going down in the bilge a wiggling everything and anything that might have to do with the tach.

Sounds like a wire problem... and not a part problem to me if the tach works at all.

 

[Mybigblue]

Thanks everybody for comments. On the weekend I will extend my investigation bearing in mind the helpfull comments so far. The yacht is a C320 Mk2 and the engine is a standard Yanmar 3ym 30 manufactured 2007. We are a little (a lot) lazy here in oz, a tachometer is often called a tacho and we just call the c320 a 32. Have to lift my game hey !
Regards Al