Wild Tachometer

[Surboum]

Any what is causing this? The tachometer for the port engine swings wildly back and forth rather than holding steady - yet the engine runs smooth. At low rpm it stays on 0 until the engine reaches about 2400 rpm. Boat is 2004 MS 430 Fast Trawler with twin 370 hp Yanmar 6LYA-STP engines. Engines have about 1,100 hours on them. Starboard engine tachometer is not affected.

 

[PhilPB]

Mine were acting a bit odd as well at different times. One on flybridge had a loose connection and the one below needed ti be replaced. Now all is good.

 

[PierreR]

I can be sensors on the synchronizer or loose connection. Does the engine synchronizer work when you engage it?

 

[kchace]

If your tach signal is supplied by the engine’s alternator as many boats are, the cause could be a loose connection at the alternator, or for some reason the alternator is operating intermittently. This can be caused by an alternator fault, or by external inputs (such as a solar panel) causing the alternator to “shut off” due to too high voltage.

Ken

 

[Comodave]

Agree, always start with the simple things first. Check for any loose connections. Also check for dirty but loose seems more likely in this situation.

 

[SteveK]

Just read another thread here and changing the oil sender solved that problem with the tach

 

[Bmarler]

I had a tach that was driven off the alternator do that before, and there was a dial on the backside of the alternator for setting the cylinder count/ calibrating the reading. I had to rotate that a few times to clean the contacts and it stabilized the reading.
Just another of many possibilities.

 

[Dougcole]

I assume it is a Faria gauge, correct? We have had similar issues with the tachs on our '05 MS 400 and my guess is that Mainship wired your boat in the same incorrect way as ours.


It's a little difficult to explain, so my apologies for the awkwardness.


The gauges are secured in the dash by a plastic bracket on the back. The terminal posts for the ground, sender wires etc, are long bolts that extend through the plastic brackets. So to install the gauge you slip the bracket over the posts and thread nuts onto the posts, the same posts that hold all of the electrical connections.


Here is the issue. Mainship put the gauges in, then put on the brackets using a nut, then attached the ring terminals on the "outside" of the brackets and secured them with a second nut. This made the gauges easier to install, but the connections come loose very easily and they don't make good contact with the gauge. And to make matter worse, as you tighten the nut the bracket flexes preventing a secure connection.


The solution is to take off all of the nuts, pull off the brackets, then put the ring terminals onto the posts and tighten them up. Some of my posts were loose as well, but I was able to tighten them.



After the wires are on, slip the brackets onto the posts and put on a second nut and washer to secure the gauge. You don't need nuts on every post to hold the gauge in place, two will work fine.


A 5/16" deep socket on a nut driver makes this job way easier. I redid all of my gauges on both the lower and upper helm.


Hope that helps (and makes sense, lol).


Doug

 

[Barking Sands]

What kind of tach signal are you working with? W signal from alternator, tach generator off accessory pad? Mag pick up off flywheel? Whatever it is I would start there and check contacts, debris and adjustments if mag pick up etc.

Since you have two engines you can also swap components side to side for troubleshooting purposes. Such as gauges to rule them out. or tach generators/mag pickups if you have that type. Most difficult to TS is W signal from alternator since its usually poor grounds or connection points somewhere along the way with a higher likelihood at the alternator or the gauge or a connector.