Rpm gauge stopped to working

[melida]

Hi all.

A month ago while I was cruising back to my home port caught in a storm for half an hour and hit some nasty waves and port rpm gauge started to bouncing and then stopped. Engine hour meter was showing but not registering the hours run while needle was at 0 rpm.

Next day of this incident in perfect weather it was sometimes showing the actual rpm, sometimes bouncing and sometimes dropped to 0.

At both times sync gauge was at the center/balance point as boat was running straight and autopilot was not needed to correct the course.

So I checked the connections at the back of both rpm gauges, 4 in 1 gauges and sync gauge but they were all tight and connections seems clean.

Also checked the tightness of the engine grounds and battery posts but they didn't needed to be tightened.






Yesterday I was doing some routine maintenance and started the engines and again port rpm gauge bounced then stopped.

So what do you guys recommend to fix this if the gauge is still alive ?

Boat is 2007 340DA(375) with twin diesel Yanmar 6LPA-STP 315 hp engines at 352 hours coupled to ZF 63-iV V-drives.

Thanks in advance.

 

[northshore]

Swap connectors for your port and starboard tachs.
If your starboard tach starts misbehaving, the tachs are fine and you will need to start looking into wiring.
If the port still has the problem, its the tach.
If they both now work fine (other than reading for the wrong engine) the connection itself might be questionable - clean them with contact cleaner.

Good Luck,

-Mike

 

[Molson]

cycle the 4-6-8 cyl switch a few times. They get corroded and the signal gets messed up.

 

[melida]

Swap connectors for your port and starboard tachs.
If your starboard tach starts misbehaving, the tachs are fine and you will need to start looking into wiring.
If the port still has the problem, its the tach.
If they both now work fine (other than reading for the wrong engine) the connection itself might be questionable - clean them with contact cleaner.

Good Luck,

-Mike

Thanks Mike gonna try them.

 

[melida]

cycle the 4-6-8 cyl switch a few times. They get corroded and the signal gets messed up.

Thanks Jim,
Excuse my ignorance can you tell me from my pics if the cylinder setting is visible.

 

[fwebster]

Your boat is a diesel boat so there is no provision on your tachs to select the # of ignition pulses which is what the cylinder selection switch does.

This sounds a lot like a failed tach to me, but there is one other thing to check after switching t he wire connections between sides: See the gray plug a short distance away from the connections on the tach? Sometimes the pins will push back in the plug housing and you will lose contact between the male and female part of the plug assembly. It is easy to push the pin back in place if one is not making contact.

Hope that helps you narrow it down.

 

[melida]

Your boat is a diesel boat so there is no provision on your tachs to select the # of ignition pulses which is what the cylinder selection switch does.

This sounds a lot like a failed tach to me, but there is one other thing to check after switching t he wire connections between sides: See the gray plug a short distance away from the connections on the tach? Sometimes the pins will push back in the plug housing and you will lose contact between the male and female part of the plug assembly. It is easy to push the pin back in place if one is not making contact.

Hope that helps you narrow it down.

Great thanks Frank.
Will try to push back them.

 

[Molson]

Apologies, I didn't catch that you had diesels. Go with what Frank said.

 

[melida]

Apologies, I didn't catch that you had diesels. Go with what Frank said.

No problem, thanks again for taking your time for my question.

 

[Woody]

That switch that says 103T, 126T, 159T is a range switch, it won't hurt to move it around. It might work just like when the gas boaters work their 4,6,8 cylinder switch. It's mostly has to do with the source of the tach input, alternator or flywheel.

I had my tachs replaced going by a mechanics test which was tapping firmly on the face of the tach. If the needle jumps it's bad. Mine jumped, I didn't know about the range switch at the time so didn't try it on mine.

 

[melida]

That switch that says 103T, 126T, 159T is a range switch, it won't hurt to move it around. It might work just like when the gas boaters work their 4,6,8 cylinder switch. It's mostly has to do with the source of the tach input, alternator or flywheel.

I had my tachs replaced going by a mechanics test which was tapping firmly on the face of the tach. If the needle jumps it's bad. Mine jumped, I didn't know about the range switch at the time so didn't try it on mine.

Thanks Woody, gonna give them a try.
My needle is not jumping when I tap it.

 

[melida]

Apologies for a very belated update due to some health/family/business issues and new site problems such as not getting notifications and can't see my own threads etc.

I tried all of the precious recommendations from Northshore, Molson, Fwebster and Woody but what they recommended was not helpfull in my problem because of my d*mbness and as being a right-handed which is broken and semi-disabled.

Last year I added a sat-tv system to my boat and put the control box right next to the glomex amplifer in the port side vberth locker which is powered via port side batteries as house-domestic/genny/port engine. The antenna and power cables of sat dome needs to be tightned well which is difficult with a tool due to where I located it and needs to be finger-tightened.

So long story short the power cable coming from the dome to the box was loose and by hitting waves became almost out of it's base and pulling too much power which stops the port tach working properly.

I tightened it with a small plier and the problem solved, tach started to show the rpm and hourmeter started to register the engine time to, and no problem since then.