Tach ??

[Esox_Magnum]

My tach on my 91 Merc 115 has a mind of it's own,most times don't work at all but sometimes it will bounce around and once in a great wile kinda work... question is bad connection/bad wire/guage or could there be an underlaying issue that needs addressed???

[Valv]

Which boat brand and year ?

[Esox_Magnum]

1991 Skeeter S-135 deep v

[morepower02]

First thing to check would be pull out the guage and check connections. If they are good locate the dial for the pole settings on the back of the guage. The settings can be adjusted using a small straight screwdriver. Sometimes we see Guages that get stuck between settings and read all over the place. With the engine running move the dial a little left or right until the tach reads correct. If it still does not work check the connections on the regulator/ rectifier on the engine.

[Esox_Magnum]

I can get to the back of the tach easily, have wiggled the wires but never taken them off and cleaned them or anything, as for under the cowl other than changing plugs and adding oil I'm lost....

[boatfixer]

Intermittant electrical issues can be frustrating. If you've checked all the connections, it could be the tach itself or the rectifier. Have you ever had problems with batteries losing charge? If so I'd lean towards the rectifier or stator. Your engine was made in an era where stators were prone to failure. However it was usually a situation where it was dead all the time and you constantly had to recharge the battery. Other times it also meant no spark. The bouncing around thing tho is interesting. Most times I have found a loose wire, pole setting switch goofed up (as mentioned above) or a bad tach.

I would eliminate the charging system first by testing those components first.

[Esox_Magnum]

Bruce, I run an onboard charger on all my batteries due to having the stereo on all the timea and at home don't run the motor enough to recharge, the only time I did not charge my cranking battery was the week I stayed on Vermilion, I only ran the charger on the trolling batteries and not the cranking and never had a problem in that week with power. I did however have power problems before I installed the radio but that I'm blaming on the Neverstart, since I put in a new Interstate it has been fine.

I do understand what the stator and rectifyer do, just no clue what they are or where they are at or how to test any of it.

[boatfixer]

I'm pretty sure if your charging system were to blame you would experience more trouble, more times than not the problem isnt as erratic as you have mentioned. Easy for me to say but I've got "test" tachs I'll hook up to verify a bad tach.

[Esox_Magnum]

Well more often than not it doesn't work at all, once in awhile it will kinda work, even more rare is the few minutes it somewhat seems to work right. Might read 3500 at WOT or 6000 but at idle will read 1000 or so or just stop all togeather. Soon as I get it out of storage I'd like to have a fix in mind for it, would like to move to a SS prop but without RPM reading nobody can give me a clue what I should be trying. Also does the 91 115 have a rev limiter on it??