tach jumping all over the place ?

[canman]

hi everyone , i have a 1996 115hp merc on our boat , the tach jumps all over , at idle it will read 5000 rpm and then it will jump all over . could it be a loose wire or some said about a setting on the back of the tach . if the tach is shot do the wires run back to the motor ? i use to have an older johnson that the wires plugged into the front of the control box .. thanks .

 

[bassher]

Re: tach jumping all over the place ?

Had same problem last year. Disconnected battery cables, cleaned and reattached. Tach fine since.

 

[canman]

Re: tach jumping all over the place ?

thanks , i have tried that , i think i need a new tach. the boat is put away in storage now , will fix in spring .

 

[Chad N]

Re: tach jumping all over the place ?

More then likely it will need a new tach. I know there are a few ways to test them but none are very great. Is the engine running fine? Best to just replace tach. Not that expensive.