tachometer question

[Jeff Walkowiak]

I believe I have a factory evinrude tach,, with the warning lights at the bottom,, it is a 1998 and was set up for a 2 cylinder 50 hp of the same year,, I just changed to a 1988 3 cylinder johnson engine, I expected to see a switch on the back of the tach to change it from a 2 cyl to a 3 cyl,, didn't really see anything other than a round slotted button that said 5 and 6 with an arrow pointing to the 6 ,, nothing indicating what the is for,, also next to the grey wire from the stator is a brown wire with a thin yellow stripe, no clue where that connects but I believe it needs to be hooked up because the tach isn't working at all now but it worked fine with the other engine.. unfortunately the wire harnesses were not exactly the same and there is no brown and yellow wire in the older harness. I have the book but the wiring diagrams really don't help.
well I think I figured out the 5 and 6 on the tach being the pulse settings and it is set on 6 ,, the wire must be the issue.

 

[HighTrim]

Re: tachometer question

Tachs read off the alternating pulses from the stator. Any of the leads from the stator charging portion can be used for the signal. The designated tach signal wire is merely attached to one of those. Tachs have rotary switches on the back (which is what you saw) that set it to different numbers of coils in the charging circuit, times two because there is a positive and negative pulse for each coil for each cycle. Tachs measure pulses.

It is easiest to check for 12-volt power and proper ground first. A volt-ohmmeter or 12-volt test light are great tools for this procedure. Simply ground the meter or light, turn the key on and touch the positive probe to the purple wire on the back of the tach. You should see 12 volts indicated on the meter, or if you?re using a test light, its bulb should illuminate. Reverse the leads to check for proper ground, or use the ground wire on the tach to ground your meter or test light.

If either the power circuit or ground is the culprit, you can repair the problem and the tach should work fine. In a no-power situation, see if your tach has an inline fuse. These often blow due to constant vibration. After inspecting for power and ground, if it still doesn?t work, it?s time to check the signal-input source.

The signal is a pulse-positive output that?s provided directly from the stator assembly through the rectifier. A peak-reading voltmeter set to ?positive? and the lowest volt scale will enable you to read any voltage output (on this circuit) from the stator.

If everything still checks out, you will need to test your rectifier/regulator as per your manual.

 

[Jeff Walkowiak]

Re: tachometer question

thank you that helps a lot

 

[Jeff Walkowiak]

Re: tachometer question

For some reason,, the stator seems to have a loose connection somewhere,, with the grey wire connected to the yellow lead with the grey stripe, the tach would not work, but after driving the boat for 20 minutes the tach started working and the volt meter started showing 14 volts,, but once the engine was turned off and re started the tach stopped working and the volt meter showed 13 volts, swapping the grey wire to the other yellow lead made the tach work all the time but the volt meter would continue to go from 13 to 14 and at one point I noticed it all the way up to 16 volts,, leading me to believe the field winding for the yellow and grey lead has some issue with a loose connection. The rectifier seems to be fine,, as it is just a simple 3 wire type but I wonder if I can upgrade it to the electronic rectifier/ voltage regulator, like the newer engines use, I will remove the flywheel today and look for any cause of the intermittent field.

 

[Jeff Walkowiak]

Re: tachometer question

another mystery solved,, the stator has a big burn hole in the plastic, where it appears to have been shorting out or arcing ,, time for a new one.

 

[asdasc]

Re: tachometer question

I love it when fixing one thing also fixes another!

 

[Jeff Walkowiak]

Re: tachometer question

well I installed the new stator,, and decided to retrofit a sea doo jet ski electronic rectifier/regulator in place of the old style diode rectifier,, started it and everything seems to be working great, motor runs smoother and a bit higher rpm at idle than it did with the old rectifier,, I have no clue as to why it runs better/smoother and about 400 rpm faster. ran it with the new stator both ways and the difference was obvious.Any theories on that.

 

[Jeff Walkowiak]

Re: tachometer question

I have put quite a bit of run time on the engine since replacing the charging coils and adapting the sea doo rectifier/regulator.. The old style diode rectifier would get readings as high as 16 volts on the volt meter and that concerned me as it could overcharge and damage both my batteries,, the sea doo rectifier is an electronic type and it works great the volt meter stays at a constant 13.5, before with the old one the longer you ran the engine the higher the voltage reading .. just thought I would pass that along .