Intermittent Problems with Rev Guage.

[Al Andalus]

Launched the boat this year, 360 Sundancer on Yanmar diesel engines, and noticed the starboard side rev counter reading a two hundred revs less than the port side. Engines seemed to be running at same speed.

Been out on a few cruises and noticed the starboard side rev counter reading 400 revs when port reading 2,000. The voltage gauge on the starboard side is also not reading correctly and seems to go up and down during the coarse of a trip. I have changed over alternators from engine to engine. Went out on a trip and initially all was running fine with both rev gauges running correctly. On our return the following day the same happened with starboard running at 400 and port running at 2,000. This goes on each time with intermittent readings.

Having ruled out alternator problems I was wondering if anyone has come across this before and if its a wiring problem somewhere between the alternator and the helm. Don't think its the rev gauge itself as the volt gauge is also showing intermittent readings on the charging side.

Any suggestions or help would be really appreciated as to where to look and start.

 

[Stee6043]

It's weird that your voltage gauge is acting up. It's very common for our tach's (rev gauge) to act wonky. Mine are very regularly all over the place. I really don't even pay attention to them. I watch speed and the sync gauge.

Many times your tach can be an easy fix. Pull the gauge and find the "cylinder selector" switch on the back. Switch it back and forth a bunch of times. While you're back there clean the connections on all the wires. Many times this will solve the tach issue (do both while you have the panel off).

I wonder if you have a voltage gauge actually going bad though. I'd start with the tach myself. See if you can fix it the easy way and then address the volt meter. If the tach is still wonky after the above procedure you may have a deeper wiring issue?

 

[ZZ13]

Power to the gauges goes through the start switch. Try reseating all the connections at the start switch. Also can swap the start switches to confirm or rule out the switch.

 

[JVM225]

Steve6043 gave you good advice for the tach. Doing it usually fixes the issue.
As far as the voltmeter is concerned, you should check voltage at a few different places.
Start at the alternator, if that’s good, move on to at the battery to make sure you are getting the same voltage at the battery that the alternator is putting out.
If you are, then it’s likely a problem at the gauge.
If the connections on the back of the gauge are good it’s probably the gauge itself.
If you don’t have the same voltage at the battery that you have at the alternator then there is probably a bad connection on one of your battery cables or terminals..

 

[Jaybeaux]

I don't have Yanmars, but my Cummins have Grid Heaters, and until the engines get REALLY warm, they will cycle ON and OFF and it will pull the voltage down on the gage.

 

[Al Andalus]

Hi JVM225 I will try doing what Steve6043 said re tach and hopefully that will fix the problem. It's just weird that we have never had problems with this in the past and both tachs have behaved themselves prior to this.

I will also look at checking the voltages at various points in case there is a problem with wiring. Had hoped that swapping the alternators over would have identified a fault with the alternator but things aren't always that simple. Oh well.

Thanks for the tips so far.

 

[melida]

Agreeing in all comments/recommendations above also check the alternator belt tightness.
As I have the same engines, there are two belts each and sometimes one is tighter than the other so you have to set them equally tight .

 

[melida]

I don't have Yanmars, but my Cummins have Grid Heaters, and until the engines get REALLY warm, they will cycle ON and OFF and it will pull the voltage down on the gage.

@Al Andalus Be sure to check the voltage when you cold start the engine(s) at the batteries if it's raising from 11.99 to 14.1 volt in a few minutes, if not your glow plugs need to be changed.

 

[JVM225]

Hi JVM225 I will try doing what Steve6043 said re tach and hopefully that will fix the problem. It's just weird that we have never had problems with this in the past and both tachs have behaved themselves prior to this.

I will also look at checking the voltages at various points in case there is a problem with wiring. Had hoped that swapping the alternators over would have identified a fault with the alternator but things aren't always that simple. Oh well.

Thanks for the tips so far.

It’s actually pretty common with tachs.
Good luck!

 

[Al Andalus]

I have a marine electrician coming down to the boat on Tuesday to try and look into this problem.

As a heads up can I ask if anyone knows if there should be a separate sender unit from the engine to the tach on the Yanmar engines ( 315 H.P LPA's Diesels) and where would I be able to look for this. I have been working on the assumption the alternators sent a pulse to the tach but as the alternators seem to be OK if there is a sender unit then my guy can check that as well as the wiring.

Thanks for your help so far but engines and electrics are not really my thing so I'm hoping this guy will be able to diagnose problem sooner.

 

[Al Andalus]

Just thought I would say thanks to everyone who helped. Have managed to get the Tacho issue resolved. My sensor is on the flywheel and not on the alternator as previously thought. Pulled the connector to the sensor and found it to be corroded, cleaned it all up, now nice and clean and working again.

 

[JVM225]

Just thought I would say thanks to everyone who helped. Have managed to get the Tacho issue resolved. My sensor is on the flywheel and not on the alternator as previously thought. Pulled the connector to the sensor and found it to be corroded, cleaned it all up, now nice and clean and working again.

That’s great!