Tach hours vs ECU hours

[spinkick63]

I got this boat at about 386 hours (per YDS). I currently have 397. Tach does not agree. It is actually showing hours value prior to me owning the boat. What would be the reason for the discrepancy? The tachometer otherwise does work as expected.

YDS:
hours.jpg

Tach:
tach.jpg

For the ones that can see it, I can't take credit for that tar/mastic/caulk/whatever on the panel. Credit goes to previous owner(s). They did some odd things to this boat.

[yam911]

Are you saying that as the ECU logs hours the same number of hours are not being recorded by your tachometer?

There could be an internal fault within the tachometer that is causing it not to record properly.

On the other hand, some tachometers record less than actual clock time below a certain RPM. I can't recall if the Yamaha tachometer does that or not.

[JJohnSind]

I thought the Yamaha tach got hours off the ECU. I gave heard that engine hours continue to rack up when the ignition is left on “on”, though. Not sure if the ECU accumulates correctly in this situation.

[yam911]

I thought the Yamaha tach got hours off the ECU. I gave heard that engine hours continue to rack up when the ignition is left on “on”, though. Not sure if the ECU accumulates correctly in this situation.

Some do. Known as Command Link tachometers.

Older version tachometers, as shown in the photo, only record their own time. Some logging time based on the key being on and some logging time based on the key being on and the motor running.

[spinkick63]

Older version tachometers, as shown in the photo, only record their own time. Some logging time based on the key being on and some logging time based on the key being on and the motor running.

Ok, so it sounds like it doesn't get data from the ECU. The only oddity is would it has lower hours than the engine. Thanks

[BroWhoop]

It's mostly like logs time when powered. It may have been powered when the engine wasn't running. I have the command link, it does connect to the ecu. Actually for years it was connected to the ecu, now it's on my NMEA network. They connect to the same port on the engine.

[Rick H]

Couple reasons I can think of.

Tach was replaced not likely but happens.

Ign. on but not running. ECM will continue to clock but the tach will not. This is how I know. Got an emergency call away while working on my boat. Forgot to turn off the ign. key just closed the garage door. Came back to it a few days later to a dead crank battery and 100 hours extra on the ECM and not the tach.

[spinkick63]

Thanks all