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Old 24-05-2012, 12:49   #1
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Tachometer Blues

My tachometer has stopped reading out engine rpm, and so I am scared to use any more than half power. I have tested both the wires and tachometer itself, each worked fine. I have determined it is either the transducer or components controlling it that are the problem. This is outside my comfort zone and so would appreciate a knowledgeable consultant.
Thanks.
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Old 24-05-2012, 13:10   #2
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Re: tachometer blues

I had same problem....studied my yanmar manual, looked a pictures, etc.
Eventually followed wiring from tach back to sender unit on the starter. Wiggled and cured. Below is a link from here

Where is the Tachometer sensor on a Yanmar 4JH3e?
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Old 24-05-2012, 13:37   #3
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Re: tachometer blues

If you are propped anywhere near correctly, dont worry, you cant over rev the engine....
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Old 24-05-2012, 15:40   #4
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Re: Tachometer Blues

Most typically a wiring fault- the spade connector on the sending unit on the engine or perhaps a corroded connection in the circuit. I had the problem and just ordered and installed a new wiring harness for a 3gm30f- thinking it would solve other issues as well.
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Old 24-05-2012, 16:04   #5
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Re: Tachometer Blues

Everyone seems to assume that you have a Yanmar engine. Is this the case? It is really not possible to help you without this info, since there are several schemes for driving an electronic tacho!

Cheers,

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Old 24-05-2012, 16:11   #6
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Re: Tachometer Blues

Most commonly on diesels it is a wire from the alternator that give tach its signal. It is a small wire, and can get loose from vibration or getting bumped when working on engine.
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Old 24-05-2012, 17:58   #7
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Re: Tachometer Blues

Greetings and welcome aboard the CF, CnC40sailor.
Presuming your screen name is descriptive - very nice boat.
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Old 24-05-2012, 19:17   #8
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The engine is a 40 hp yanmar diesel. Sorry for not clarifying this earlier
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Old 24-05-2012, 19:22   #9
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Originally Posted by GordMay
Greetings and welcome aboard the CF, CnC40sailor.
Presuming your screen name is descriptive - very nice boat.
Thanks! And again thank you, I thought that myself when I bought the boat . Personally the classic sheer and round hull (doesn't carry the beam aft) are, to my eye, much more attractive then the new straight styles.
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Old 24-05-2012, 19:30   #10
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Quote:
Originally Posted by Seaduction
Most typically a wiring fault- the spade connector on the sending unit on the engine or perhaps a corroded connection in the circuit. I had the problem and just ordered and installed a new wiring harness for a 3gm30f- thinking it would solve other issues as well.
I was really hoping this wasn't the case, as it is an old boat with multiple owners. These owners appeared to have been fairly lazy as there is an endless amount of unused wires everywhere. This all corrolates to lots of work. Then again, it is a boat, so nothing new!
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Old 24-05-2012, 19:39   #11
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Quote:
Originally Posted by CnC40sailor

I was really hoping this wasn't the case, as it is an old boat with multiple owners. These owners appeared to have been fairly lazy as there is an endless amount of unused wires everywhere. This all corrolates to lots of work. Then again, it is a boat, so nothing new!
Ah... the inheritance of someone else's 30 y/o wiring. Good luck...
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Old 24-05-2012, 20:07   #12
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And I always told my kids inheritance was a good thing....boy are they in for a shock!!
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Old 24-05-2012, 20:14   #13
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Re: Tachometer Blues

OK, it is a Yanmar. IIRC, Yanmar has used both alternator driven tachos and ones driven by a magnetic pickup on the flywheel. No experience with the latter but some with the former.

If alternator driven, is it the original alternator, and the original regulator? These things will help in narrowing down the cause of your problems...

Cheers,

Jim
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Old 25-05-2012, 07:14   #14
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I can tell you right now the entire engine is stock. I'm not sure if its alternator or not, although this seems to be what I'm leaning towards. I'll have to go out and check to be sure, I've just had a lot of work lately and so been forgetting the simplest things, sorry for the inconvenience.
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Old 26-05-2012, 20:08   #15
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Yep tach is alternator driven. Sorry for the hold up
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