Volvo Penta tach not working

[landonshaw]

I have a Volvo Penta MD2040D, two alternators, both identical and standard Volvo. My tach continually shuts down. I have been told that when the batteries are fully charged, the Volvo has a flaw that the tach will then shut down. My batteries are up to 14.2. Besides the tach not working, the engine he counter also does not work properly. It is digital and generally flashing all sorts of numbers. The tach has always not worked well even when the batteries are not fully charged.

A few years ago I purchased a new Volvo tach, no change to problem. Any ideas?


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[Paul L]

When the regulator shuts the alternator down because the batts are full you can loose the tach signal. With no solar, try putting a load on the system like turning on an incandescent light. This may enable the alt and thus the tach.
The issues with the hour counter sound like you have a bad connection. Maybe a corroded ground?

[belizesailor]

Agree. Maybe a combination of regulator and a ground/wiring issue. Dropping the tach signal is not a Volvo specific flaw, many regulators do this.

No change with new tach, so almost certainly eliminates the tach as the issue. The hour meter issue you describe is a common mode of failure of the display, but given that the display is built into the tach (yours is right?) then that points to a different source for this problem too.

Induce a signficant load as suggested, if either or both issues go away then its likely caused by the regulator.