Tachometer

[LPL]

I have a 2008 Yanmar 4JH4AE with about 2200 hours on it. When new I paid the $700/800 upgrade from their dummy light panel to the C panel with the needle gages on it. My problem now, is the tach sometimes (but not usually) goes crazy, then will settle down when throttle is changed. Also, when I shut down the engine, it will stay just above the 0 mark unless I wait for the buzzer to come on before I turn the key off. I would assume this would indicate a bad connection somewhere, but the wire connections are clean. (When new, I had to replace the bulb on the temp. gauge, and had to replace the bulb on the oil pressure gauge at 2000 hours--3 years). It is protected from the elements. Any ideas what to check?

Thanks for your help,
Paul

[sww914]

I would run a separate ground temporarily to see if that changes it. Just a simple wire from the battery negative straight to the gauge ground terminal. Don't drill any holes or anything, just lay it over the stove, through the shower, over the boom, or through the holding tank vent line or whatever it takes. Hell, I wouldn't even bother putting any ends on it, just strip back the wire and jam or hold it in place for a minute.

[landonshaw]

Glad you posted. I have a Volvo Penta and the tach periodically shuts down or will bounce from 0 and up then shuts down to zero. It will then resume normal operation. I have cleaned the terminals but still I have the problem. Purchased a NEW tach and it operates the same. No bulbs brining out though.

[bstreep]

I knew I'd seen this before, so I did a search:

Are you sure the tach is bad? How do you know? Here is how to test. On the back of the tach are two leads that come from the flywheel. Mesure htz or volts (both will work across these leads. Should ramp up with rpms. If so the tach is bad. If not then go to the left side of the engine on teh flywheel housing and loo for a big sensor plug. Wiggle the wires and watch the tach. In fact do that first. This is where 99% of the Yanmar tach problems start, at the sensor wires at the engine.

[delmarrey]

I would have the alternator tested. That's what the tach runs off of and with 2200 hours it might be due for some brushes.

[LPL]

Thanks for the replies and suggestions. DelMarrey: The alternator brushes sound like a good bet. I was going to have the alternators serviced when we return to Texas in the next couple of weeks, but I had forgotten the tach runs off the alternator. I appreciate the help.

[Stu Jackson]

If your batteries are fully charged from being plugged into shorepower or you have solar, the tach's regulator will not require alternator ouptu, hence, a floppy needle on the tach.

[Wotname]

Originally Posted by Stu Jackson

If your batteries are fully charged from being plugged into shorepower or you have solar, the tach's regulator will not require alternator ouptu, hence, a floppy needle on the tach.

???? can you explain this in more detail ????

[Rakuflames]

Originally Posted by delmarrey

I would have the alternator tested. That's what the tach runs off of and with 2200 hours it might be due for some brushes.

This place is absolutely INVALUABLE!!!

[Stu Jackson]

Originally Posted by Wotname

???? can you explain this in more detail ????

Sure. How a regulator works (simple version with no electrickery involved) is that it checks the voltage at the alternator output (internal regulator) or the house bank (external regulator). If the voltage being checked equals or exceeds the setpoint (usually around 14.2 +/- V) then the regulator says "I'm happy, no need to start charging."

It's pretty much that simple.

You can do a simple test. Completely charge your house bank at least overnight and make sure it's full.

With shorepower still plugged in, and charger on, and NO DC loads on, start your engine. The tach "most likely" but not always will do nothing.

Stop the engine, unplug shorepower (or turn your charger off) and run some loads up to 5 or 10A, like the fridge, lights, etc. for 20 minutes or so.

Then restart the engine. The tach should be working.

The way this question usually comes up is this: "I just started my engine and the tach isn't working. What's wrong?!?" The answer usually is: "Are you still connected to shorepower with your charger on and/or are your batteries full?"

Many people will be aghast that I'm suggesting starting your engine with your charger still on. Nonsense. Many folks have more than one means of charging, like solar, wind, alternator and shorepower. I've never heard of anyone disconnecting their solar panels when motoring...

Does that answer it for you?

[landonshaw]

I mentioned my tach problem to a friend and he suggested that I spray an electrical solvent into the key switch. My tach will shut down periodically, bounce up, shut down eventually run at the correct RPM, it is a new tach, Volvo Penta. He said that twice his tach behaved this way and he ended up having to replace the key switch and that also then fixed the tach. I tried it, went out this weekend up north and the tach worked wonderfully. Now, it might be a coincidence, maybe not, I will keep you posted if the problem returns.