VP MD22 rev counter

[FlyingDutchman]

When I switch on the contact of my Volvo MD22, the rev counter flips to maximum (5000 or so). When I start the engine, the counter drops back to 800 rpm after 15-20 seconds. I have checked the electrical connectors behind the dashboard and on the black relay / fuze box on the engine and all these seem to be in good shape. Funny thing is that it usually does not happen when I start the engine for the second or third time on the same day.
Any ideas highly appreciated!

 

[Richard10002]

Has this just started happening, or has it happened since you have owned the boat?

 

[FlyingDutchman]

Last year and the year before it happened a couple of times, but this year it happens nearly every time. Any idea? Would it do harm to the rev counter?

 

[Richard10002]

I dont know..... I just thought my question might help others with more knowledge to answer.

I've just done a lot of diagnostics on why my rev counter wasnt working at all, so hoped I would be able to help - but I've no idea... sorry

Richard

 

[FlyingDutchman]

Thanks anyway.
Do you have any idea where the tacho gets its signal from? The alternator?

 

[Richard10002]

[ QUOTE ]
Thanks anyway.
Do you have any idea where the tacho gets its signal from? The alternator?

[/ QUOTE ]

On my MD22L -A it's from the W terminal on the alternator.... on mine it is a single grey wire which goes directly from alternator to rev counter. Whilst it's an alternating signal, a DC meter reads about 7V at the rev counter, (presume it reads the same at the alternator /forums/images/graemlins/smile.gif ). Everything else at the alternator reads the boats voltage.... around 13v.

Alternator

Back of rev counter

Over to the experts /forums/images/graemlins/smile.gif

Richard

 

[FlyingDutchman]

Thanks Richard,

Do I understand correctly that the grey wire gives power to the rev counter?
That would mean that this wire can not be the source of my problem since the tacho reads 5000 rpm when the engine is not running.

Jan

 

[Richard10002]

[ QUOTE ]
Thanks Richard,

Do I understand correctly that the grey wire gives power to the rev counter?
That would mean that this wire can not be the source of my problem since the tacho reads 5000 rpm when the engine is not running.

Jan

[/ QUOTE ]

No.. the grey wire, (or the wire from the W terminal on the alternator), just provides the signal. Power comes from 2 of the other wires, (the bottom two, black and blue, on my rev counter socket thing).

The red wire to the side of the socket provides a small amount of power when I turn the engine off, and this zeros the needle. With the red wire disconnected, the needle remains where it was when I turned off.... usually around 800 revs.

 

[FlyingDutchman]

I did not know that the counter needs power to bring the needle back to zero!
It remains a mystery though why mine jumps to 5000 as soon as I switch on the ignition. I do hope the counter is not kaputt as this will be an expensive operation...
Many thanks for sharing your knowledge!

Jan