Tachometer reads wrong

[harveyb]

I have a 2003 Yellowstone Quatro 40 foot motorhome 330 cummins and last trip in I noticed tech reading very high rpm's after check temp gauge I stopped walked back to engine rpm sounded normal. shut down engine after an hour or so restarted and it was fine. A week later ready for a trip and when I started it read way off again always high now it seem to be starting in the middle of the gauge and 60 mph it reads off the scale. Any ideas?

[Restorium]

I have a 2003 Yellowstone Quatro 40 foot motorhome 330 cummins and last trip in I noticed tech reading very high rpm's after check temp gauge I stopped walked back to engine rpm sounded normal. shut down engine after an hour or so restarted and it was fine. A week later ready for a trip and when I started it read way off again always high now it seem to be starting in the middle of the gauge and 60 mph it reads off the scale. Any ideas?

I would find the tach wire leading to the tach and check to see if another tach reads the same while connected to the wire. That would tell you if it's just the tach or the signal to the tach.
Over the years I have had tachs on different vehicles act strangely when there's a short in the engine harness. And I have also had tachs act strangely like described when they needed replacing, faulty.

[harveyb]

Thanks will check it out.