Tach, jumping why?

[grewvin1]

1987, merc. 5.7L twins, wellcraft Monte Carlo.
Would like to know typical reason why the tach's will jump and settle from time to time. Start up idle 1,000rpm for warm up and tach needle will jump to 3,000 or more then back and jump again. After warm up and slow idle out of slip to lake tachs again from time to time will jump and then when running say 3,000 rpm cruise they will stay true and fixed and work well till the next day and start up. Have cleaned many of the connections, looking for insight to the reason so over the winter plan to remove the inst. cluster and re-do and clean all wire connections to all gauges.

 

[Don S]

Re: Tach, jumping why?

If the engine isn't missing when the tach jumps, it's probably a loose connection somewhere, or a defective tach.

 

[grewvin1]

Re: Tach, jumping why?

What is the round box with all the wires running from/to it connected to the engine syncro gauge? it is black near to 5" in diameter.

 

[Don S]

Re: Tach, jumping why?

Have no clue. Post a picture of it.

 

[edsmax]

Re: Tach, jumping why?

Remove the tach from the helm and spin the selector "wheel" in back a few times. The wheel I am referring to is used to select 8Cyl, 6cyl, etc etc. Once you see the back of the tach, you will know what I mean. This will clean some internal contacts inside the tach and usually remedies the jumping tach syndrome. Good luck.

 

[grewvin1]

Re: Tach, jumping why?

Know the dial you mean will give it a go thanks good thought.

 

[grewvin1]

Re: Tach, jumping why?



herer is a copy of the item for the tach syncro. system

 

[jumpjets]

Re: Tach, jumping why?

My 1990 wellcraft used to do the EXACT same thing. I think the wellcraft tachs just go bad after a while. I tried cleaning and tightening connections, etc.... all with no avail.

I just installed a new tach, and the problem was solved. I used all the same wiring, and just screwed in the new tach.