# Mercury tach issue



## ajhallfr (Jan 1, 2014)

I've got a 1995 mercury 115 hp 2 stroke outboard tachometer issue. I bought the boat in 2016 and the tach never worked, but I didn't think anything of it. This year, the darn thing kept dying when I shifted to neutral. I adjusted the idle and it's not dying anymore, but that got me thinking that I should have a working tach.

The issue: tach either reads 0 or reads around 5400 rpm. It goes from 0 to 5400 about the point the boat goes on plane, no matter the throttle. I've done a ton of searching and can't figure this out. Does anyone have any clue?


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## kroppe (May 7, 2000)

Loose connection at the cockpit or engine ends?

Pinched wire between cockpit and engine? 

Have you done the “wiggle the wire” test while idling, to see if anything happens?


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## ajhallfr (Jan 1, 2014)

kroppe said:


> Loose connection at the cockpit or engine ends?
> 
> Pinched wire between cockpit and engine?
> 
> Have you done the “wiggle the wire” test while idling, to see if anything happens?


I have checked the connections at the tach end, I'm avoiding the engine if I can, that's my last resort. I was hoping someone here had the same issue and it was an easy fix. :banghead3


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## kroppe (May 7, 2000)

Why are you avoiding the engine end? What if it is as simple as a loose wire?


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## bowhunter426 (Oct 20, 2010)

I have a similar year 115 and have a somewhat similar issue. Tach works until 4000rpm and then jumps to max rpm on the tach. The tach counts pulses from the stator. Verify all the wires are tight on the Voltage regultor. I think my issue might be a bad tach as the VR tests ok with a multimeter


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## ajhallfr (Jan 1, 2014)

kroppe said:


> Why are you avoiding the engine end? What if it is as simple as a loose wire?


I've got to take more things apart than I want to to get a good look. I have a tendency to mess other things up when I really star messing with things, lol.


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## ajhallfr (Jan 1, 2014)

Update: I checked as many things as I could in the engine. The wiring to the stator looks good, along with all other wiring and connections I could find. As one can most likely figure out, I'm not mechanically inclined, and as such could not locate the voltage regulator/rectifier to check that. I feel like it may be behind my oil reservoir?

My next step is going to be to recheck wiring and connections from the tach back, and then buy a cheap tach to test if it's just bad.

If anyone has any other advice or can tell me where my voltage regulator is I would greatly appreciate it.


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## kroppe (May 7, 2000)

This points to the rectifier: https://forums.iboats.com/forum/eng...mercury-force-1996-115-tachometer-not-working

You are looking for something that looks like this: https://www.amazon.com/Regulator-Rectifier-1989-1997-1988-2000-1989-2006/dp/B00DBDW43E


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## ajhallfr (Jan 1, 2014)

Kroppe, thank you for all the help. You're finding stuff online that I haven't been able too.

I did locate the regulator/rectifier. I looked right passed it on my initial look as it's not next to all the other wiring. It's located on the top front left side (next to the oil fill).

All the wiring for it looks great. I'm about to pull it off and check the unit itself, but I'm hesitant to think that's the problem as the volt meter and the voltage reading on my graph read what I think they should when the boat is under power, between 13 and 14 volts.

Again, I want to thank you kroppe. Keep the advice coming.


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## kroppe (May 7, 2000)

If it were mine, I would pull the rectifier off and look at it. From what I see online, it is fairly obvious whether or not it is fried. Your diagnosis needs to affirmatively rule things out, step by step. Visual inspection of the rectifier will rule it out as a cause, or it will be the cause.


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## CrawlerHarness (Dec 9, 2017)

It is not always obvious to the eye when a rectifier is fried. 

If the battery is reading 13.0-13.5 V when the motor is running at idle, and 13.8-14.2V when the motor is running at >75% throttle it should be good. 

If the Voltage goes above 14.5 V at any point in time, or if your Voltage drops off from the >13.5 when running at 75% throttle, then it is likely bad. When rectifiers start to go bad, they usually still work intermittently.

I can't say whether it is the rectifier or not though. I haven't come across the rpm issue described. I wonder if your rectifier is losing its ground at times.


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## ajhallfr (Jan 1, 2014)

Final update: it appears that the problem was a bad tachometer. I replaced the old one (the original, produced in 94 based on the stamp on the side) with a new one and fired up the engine. It appears to work on idle. Hopefully I'll be able to get the boat out and give it a real test soon. The other test is seeing if my second rate wiring holds up as well.

Thanks to everyone that helped me out with this!


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## kroppe (May 7, 2000)

Congrats. Please post the result on the water at speed. My tachometer is flaky at high rpm, but works fine at idle. I have done a once-through of the wiring, and it all looks good. I may need to replace the tach also.


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## ESOX (Nov 20, 2000)

kroppe said:


> Congrats. Please post the result on the water at speed. My tachometer is flaky at high rpm, but works fine at idle. I have done a once-through of the wiring, and it all looks good. I may need to replace the tach also.


My tachometer isnt worth a crap, hasn't been for years.. But I have no desire to replace it. I know I'm propped properly. The rest is nonsense to me. If I ever need to reprop and they dont make this exact one anymore, I'll fix the tach.


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## ajhallfr (Jan 1, 2014)

ESOX said:


> My tachometer isnt worth a crap, hasn't been for years.. But I have no desire to replace it. I know I'm propped properly. The rest is nonsense to me. If I ever need to reprop and they dont make this exact one anymore, I'll fix the tach.


LoL, I had some spare time and needed something to do. I spent the end of March and April fixing a snowmobile that wasn't broke. I like to tinker, it's the only way I can learn something new.


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## CrawlerHarness (Dec 9, 2017)

ESOX said:


> My tachometer isnt worth a crap, hasn't been for years.. But I have no desire to replace it. I know I'm propped properly. The rest is nonsense to me. If I ever need to reprop and they dont make this exact one anymore, I'll fix the tach.


I thought the same thing....until my 70hp Johnson was showing 3400 rpms at WOT. I couldn't figure out why. Everyone here said replace the prop. That was a waste of $120. They also said replace the coil pack.....I skipped that. Turned out that my top cylinder wasn't getting gas, of course still showing 110 psi. The tach on a boat can help troubleshoot.


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## Shoeman (Aug 26, 2000)

True that!

But you already knew it wasn’t getting up to speed, 

Unless you change running gear, add a jack plate or trim to extremes who needs one?


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## bowhunter426 (Oct 20, 2010)

CrawlerHarness said:


> I thought the same thing....until my 70hp Johnson was showing 3400 rpms at WOT. I couldn't figure out why. Everyone here said replace the prop. That was a waste of $120. They also said replace the coil pack.....I skipped that. Turned out that my top cylinder wasn't getting gas, of course still showing 110 psi. The tach on a boat can help troubleshoot.


He has a Yamaha. They don't ever need repairs.

I personally like having the tach to make sure I am operating in the ideal operating ranges. Whether it be 3000rpm cruising for best fuel economy or running it to the 9000rpm limit for top speed


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## ESOX (Nov 20, 2000)

After all these years I drive by ear and ass. you can always get the best trim and throttle setting for the conditions using those two.


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## piketroller (Oct 24, 2016)

ESOX said:


> My tachometer isnt worth a crap, hasn't been for years.. But I have no desire to replace it. I know I'm propped properly. The rest is nonsense to me. If I ever need to reprop and they dont make this exact one anymore, I'll fix the tach.


Does your engine have a NMEA 2000 connection on it? If so, you can run a digital tach and many other sensor read outs on your fish finder. My main running screen has RPM, hours, engine water temp, instantaneous fuel efficiency, and trim, along with SOG, depth, and lake water temp. The only thing on the dash I look at is the fuel needle.


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