Yanmar RPM Gauge Issue

[theway]

Here is my Gauge (it's not pretty).
The problem I'm seeing is that sometime it doesn't work, it just shows 0 while the engine is running. This usually happens on startup but starts working a few minute after cranking. It rarely stops after its started.

I've checked the wiring on the back of the gauge and where it plugs into the engine, they seem fine. So I'm wondering if the gauge is going out. Another reason I think it's the gauge because when it turns on it does it on its own now because I'm messing with the wires.

Any thoughts? The engine is a 3gm30.

Thanks.

[Cheechako]

Do you have an external regulator on your alternator? This will often do it. The rpm wont show until the regulator kicks in, sometimes at higher rpm. It's pretty common.

[theway]

Yup, Balmer. I do notice when it kicks on and the little delay. But the RPM gauge doesn't always start right when the power kicks in...

But yes, I think the gauge usually starts working when I up the engine speed. I guess the times when it takes longer to start working I'm running at lower RPMs. Ok, that makes me feel better.

Thank you.

[bill good]

Very common problem. Pulse generator is from magnetic pickup on flywheel. 2 wires & the tacho needs a pos 12v & a earth back to the motor for the neg. Also the harness becomes brittle with age & heat. The two plugs & sockets are a source of intermittent problems.
Regards

[Cheechako]

So, based on my post and Bill Good's post you need to determine if yours is being driven off the engine pulse or from the alternator. If I remember right you can see the pulse sender on the flywheel housing (?) Check it out and see if there is one, and if there are any wires still going to it... or if those wires go anywhere...

[theway]

If I remember correctly it's the connection in the center of the photo. But it's difficult to follow the wiring.

[Cheechako]

That's it. try disconnecting it and see if the tach works at all. If it doesn't work disconnected then I would assume that's your sender.

[sailorchic34]

Very common to get corrosion between the spade connectors on the sensor and and the wiring female ends.

[theway]

I'll give it a try and look soon.
Thank you.

[GordMay]

➥ Magnetic Proximity Tachometer - Tachometer Wiring Diagram Cruisers & Sailing Photo Gallery

[laika]

Originally Posted by theway

If I remember correctly it's the connection in the center of the photo. But it's difficult to follow the wiring.

Attachment 95277

My 3gm30f had untinned wire and after 10 years was in very poor shape. If yours is like mine, that trailer connection in the bottom left of the photo is heavily corroded. I ended up pulling mine out and just re-wiring the entire dammit. YMMV

[GordMay]

See ➥ Troubleshooting Teleflex Tachometer Gauges

[dtlx11]

We have the same engine, the same display panel and the same problem.

Let me know if you get it fixed, my problem goes further in that nothing on my panel works apart from the starter button. No revs, no oil pressure alarm no temperature alarm and no water pressure.

I've checked all the connections and wires against the wiring diagram in the manual and it all looks good but nothing works.

[deblen]

Treysit Sirometer Vibration Tachometer | eBay

A sirometer is a useful tool for checking/calibrating RPM.

[Sailorman Ed]

Glad to see this as I also have this on my 2GM engines, intermitted RPMS. Will check the above suggestions. I also have a buzzer problem. At first it was the water sensor for the SB saildrive but I disconnected it and now I have a quieter alarm sounding (with the water sensor disconnected) Not an overheated engine as it starts right away. 600 hour on the engine. Suggestions?
Ed