Tachometer Fluctuation

[sailcapt340]

2000 Hunter 340 …..On my Yanmar 3GM30F, the tachometer has started to fluctuate. This has happened twice before, years apart in events.
It is more annoying to watch than it is critical.
It’s not a digital reading, it’s the original analog tachometer with hour meter.
What happens is the reading just isn’t right.
Normally I idle at 900 RPM and cruise at 2500 - 3000 RPM.
Today my 900 RPM reading was 1500 and my cruise reading was 4000 RPM. (I was pegged out!)
The engine is running the same and is quite easy to run by sound rather than actual RPM readings.
I did what I have done in the past when this happened. I took the 2 connectors off the sensor on the transmission, cleaned them with a quick wipe of emery cloth and put them back. Now all is good again.
In fact the connectors looked bright and clean when I removed them, fit tight and snug. I checked the same at the tachometer and they were clean as well.
Is anyone else having this experience with their tachometer?
Are you applying any spray sealer on the connected fittings?

 

[dlochner]

Yep, I've got a randomly reading tachometer on my Yanmar 3JH2e. There is probably corrosion inside the wire that increases the resistance in the wires. One of these days I plan to replace the wires from the sensor to the tach. Another Yanmar harness failure.

 

[sailcapt340]

Big job to say the least. I want to avoid that if at all possible. That‘s akin to the intermittent starter button connector issue. Which, on my boat, sits right next to the tachometer sensor. Both being in very tight quarters and very limited wire access.
If that’s my only recourse I guess I’ll have to do it as well. But not going to be happy.

 

[dlochner]

But not going to be happy.

When was any sailor happy fixing OEM crap?

Just think how happy you will be when the tach is working again.

 

[Johnb]

I spray the contacts with Deoxit D5. It has given me excellent results but I have no idea if it is the best.

Be warned, it is very penetrating and loves to get into LCD's and ruin stuff like clocks, scales etc so use with care.

 

[kloudie1]

There are two multi wire connectors in the harness between the sensor and the tachometer. Clean and check the sensor wires in those connectors as well.

 

[sailcapt340]

There are two multi wire connectors in the harness between the sensor and the tachometer. Clean and check the sensor wires in those connectors as well.

I wish I could find them.
I have been in the wiring harness years ago to fish a new wire up to my console for a horn button but never saw any connectors. Of course I wasn’t looking for them so they are in there somewhere.
And I did go through the harness in the other direction to route a GPS antenna cable to the rail in my stern seat. All jobs I would rather not do again.
But in this case….I will be forced to tackle a winter project.
And as Dave mentioned, Imagine how happy I’ll be.