Can't get signal for tach

[FuriousMob]

I picked up a tach today to replace the one that didn't appear to be working. I have the same issue now as the original that I replaced. It gets power (needle hits 0 when power is supplied), and the light works, but doesn't read a thing. I have it set to 6p, I should have 12 poles on my 89 Evinrude 100 STL.

I checked the connections for the send wire (gray), and replace one, which was fine, but wanted to be sure. I checked the connection in the engine, cleaned it up, but it appeared to be fine as well. Besides the wiring harness connection, that is all the points where a connection could fail from what I can see.

I might have to take it to my old mans this weekend and have him use his oscilloscope to see if it's even sending a signal at the engine connection. Unfortunately it's an hour drive to his place, so it eats up some gas for the drive...but at least I can launch from his neighborhood ramp if I get working! Everything seems to be working great other than this.

Anyone have any other ideas on where I might want to check? The service manual isn't much help at all. I've looked through other posts and checked what I could from the suggestions there.

 

[Barnacle_Bill]

Re: Can't get signal for tach

Test your rectifier. When the diodes in it shorts out it kills the signal to the tach.

 

[FuriousMob]

Re: Can't get signal for tach

Thanks...from what I read, if I get good voltage when running the engine, the rectifier is good. At idol the voltage crept up to 14+ volts. I also found something that said you can test the send signal using AC and it should read between 5-7 volts. Something I'll look at tomorrow.

 

[FuriousMob]

Re: Can't get signal for tach

I tested the send, and getting about .2 volts AC, and it's supposed to be 5-7. So I tested the stator, and the service manual says 0.7 +/- 0.05 ohms testing yellow and yellow/gray. I got about 0.1 so that worried me. It also said to test each wire separately while grounded and it should get infinite ohms on high ohm setting, but I was getting 21k. I decided I tried to figure out the ammeter test, but didn't feel comfortable the connections using the multi-tester. In that process I had loosened and re-tightened the starter solenoid battery connection and the read lead from the rectifier on the terminal.

At this point I checked my deep cycle, which was below 12.5 volts @ 12.4. So I figured I'd monitor that to see the voltage reaction while running on the deep cycle. While watching it slowly creep up to about 12.8, I happened to turn around and notice the tach was working. I moved the idol up and it reacted. I shut down, switched back to the main battery, started her up, and the tach again was working.

Is it possible that any of those connections I messed with on the terminal would have "fixed" the tach issue (stator yellow & yellow/gray, rectifier red)?

Also, now I have to go back and find out why the stator ohms readings weren't correct. The thing is, everything works fine, on the main battery it raises to ~14.5 volts when at a slow idol.

 

[Barnacle_Bill]

Re: Can't get signal for tach

Did you have the stator wires disconnected when testing? Yes you could have a bad connection or crimp on one of the lugs.

 

[FuriousMob]

Re: Can't get signal for tach

Yes, I disconnected the stator wires from the terminal before testing.

Is it normal for the tach to not respond right away after starting the engine? It takes a about 30 seconds before it kicks in on cold start. On a warm start, it's working right away. If it's not normal, maybe there is a connection loose elsewhere that firms up when the metal expands from warming up.