Tach reads at idle but not at speed

[great_white_fisherman]

My tach will show rpms when at idle, it even responds well when I pull the cold start lever. But when I'm running, it pegs out flat, reading 0. What's going on here?

 

[Scott Danforth]

going to make a big AssUmption here since you have a cold start lever you are working on a boat with an outboard

any of the following 3 reasons would cause it

you have a bad connection and are loosing signal or voltage/ground to the gauge
your charging system is dropping out which is dropping the signal
you have an issue with the tach

 

[great_white_fisherman]

I recently bought a volt guage, will install soon. Will that tell me if my charging system is dropping out? What should it read if it's charging right, 14?

 

[dingbat]

I recently bought a volt guage, will install soon. Will that tell me if my charging system is dropping out? What should it read if it's charging right, 14?

What motor?
Stators typically work or they don’t.

I’m leaning more towards a voltage regulator or power pack problem.

 

[great_white_fisherman]

Its an 87 Johnson 110

 

[great_white_fisherman]

I did the first of a few tests, the ones I could do on muffs. Others require going at speed.

First off, I had my volt meter hooked to the battery to see what was going on with the charging circuit. The good news is that my battery did return to its original voltage and very slowly climbed up. I'm talking a few minutes to go from 12.69 to 12.70....that was the highest I could get, no 13 or 14 like I expected. That was at idle, between 1500 and 2000 rpm (according to the tach) using the fast idle lever. Next test is on the water at higher rpm.

Second, I kept an eye on the tach to see what it would do. I tried replicating the dead tach problem to find where the issue is. I tried shifting gears, no change, I watched as I throttled it up with the lever, no change. At least, no pattern. Because at one point I looked at the meter and looked back and the tach had died. I lowered the rpm and it came back. Raised it and watched waiting for it to do it again. Nothing. It didn't die at all for the rest of the time I ran it (about 5 more minutes waiting for voltage to move).

Another thing that puzzled me...when I shut off the motor I forgot to remove the test leads and came back a bit later and it read 12.74. It went up after shutting down! What?! But it also went up (SLOWLY) when running, never down like it was being drawn off. I'm confused with that one...
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As far as the tach, I'm going to give all the connections a good steel brushing and see if that fixes anything. Because the dead tach is definitely intermittent and I was unable to replicate a pattern for it. Here's to hoping.

 

[dingbat]

First off, I had my volt meter hooked to the battery to see what was going on with the charging circuit. The good news is that my battery did return to its original voltage and very slowly climbed up. I'm talking a few minutes to go from 12.69 to 12.70....that was the highest I could get, no 13 or 14 like I expected. That was at idle, between 1500 and 2000 rpm (according to the tach) using the fast idle lever. Next test is on the water at higher rpm.

Second, I kept an eye on the tach to see what it would do. I tried replicating the dead tach problem to find where the issue is. I tried shifting gears, no change, I watched as I throttled it up with the lever, no change. At least, no pattern. Because at one point I looked at the meter and looked back and the tach had died. I lowered the rpm and it came back. Raised it and watched waiting for it to do it again. Nothing. It didn't die at all for the rest of the time I ran it (about 5 more minutes waiting for voltage to move).

Sounds like an issue with the stator or voltage regulator. A good battery will measure 12.7+ VDC at rest. You should be pushing 14V with the motor idling.


My theory is that your leaking VAC into the tachometer circuit causing interference. Problem would vary with RPM.......Suggest to you run the troubleshooting test on the voltage regulator/rectifier outlined in the repair manual

 

[great_white_fisherman]

Results of the water test:

The tach works off and on. When it does work, it appears to be accurate enough. But who's to say. It works when it wants and I can't find any kind of trigger or pattern to it cutting in and out. It's just random...

Now the charging system, I don't know. The tach shouldn't be able to work if the charging system isn't working right? But it would seem that it isn't working. Running around 3500, I still didn't get even close to 14. Reading was 12.8 and it wouldn't budge. So how can the tach even remotely work if the charge system is bad?? Maybe it's a weak charge?

 

[great_white_fisherman]

Sounds like an issue with the stator or voltage regulator. A good battery will measure 12.7+ VDC at rest. You should be pushing 14V with the motor idling.


My theory is that your leaking VAC into the tachometer circuit causing interference. Problem would vary with RPM.......Suggest to you run the troubleshooting test on the voltage regulator/rectifier outlined in the repair manual

I plan on doing the diode test after seeing the results of my "does it work or not" test today. If anything is bad, I hope it's the regulator because I can replace that myself. I can't do the stator...

 

[Tassie 1]

Son recently had a similiar problem with his 1996 115 'Fast Strike ' Johno,
Tach would work intermittently or not at all...as well the batteries were losing charge while out boating,

He did some research, including on here,
As the above posts mention look at the voltage regulator,

Son replaced his and everything now works as it should.

 

[great_white_fisherman]

Anybody have the torque values for the regulator bolts?