Need help with Tach

[rekogniz1]

My old Tack was somtimes working and somtimes not working and then nothing so I purchased a new one. I installed the new one and it does nothing also. Well it does zero out like it when I turn on the key, but thats about it. Here is what I know from testing wires:

1. Gets twelve volts and good ground even tried battery ground and 12v to eliminate those two
2. Did continuity check on the grey sender wire from the tach all the way back to the motoe where it goes into a regulator or rectifier of some kind.
3. When I turn on the ignition to start and crank the needle jumps to 1k but then drops back down to zero again while motor is running.

Any ides what to test next? All my other gauges work (MPH, Tilt, Volts etc)

 

[bktheking]

Re: Need help with Tach

What motor? Did you adjust the new tach (should be a POT switch on the tach) to match the pulse/poles of your motor?

 

[rekogniz1]

Re: Need help with Tach

It is a 1991 evinrude 150. Yes I did set the mag setting. The thing is the old one was not working either when I took it out.

 

[bktheking]

Re: Need help with Tach

Is the rectifier/regulator good? Usually when the tach stop's working it isn't working or the tach isn't working, you've eliminated the tach, so.....

 

[wilde1j]

Re: Need help with Tach

To quick check for R/R, measure voltage across battery terminals while running at fast idle. Should get 13.5 vdc or >.

 

[rekogniz1]

Re: Need help with Tach

Yes, I am getting 13.5 or greater accress the batt when fast idle. The wierd thing is the old one would work somtimes and then nothing so I just figured it was the tach but now even with the new one installed all it does is zero out when I turn on the key. What else should I check besides the battery? Is there a way to put a meter on the send wire and check to make sure that it is actually doing anything? I do have a multimeter with a bunch of different settings, so maybe there is a way to check that wire while the motor is running, i just dont know what setting used to check this or what values to look for?

 

[wilde1j]

Re: Need help with Tach

I think the sensor pulses are square wave dc, but not sure of the voltage levels. You may need a DVA (peak picker) to read anything on a VOM.

 

[ezeke]

Re: Need help with Tach

Testing the charge won't help if one side of the rectifier is bad, which is very likely. Take the gray wire and move it to the terminal block on the engine where you will find two yellow wires. If the rectifier is good, the tach will work on either of the yellow wires. If not, replace the rectifier.

 

[rekogniz1]

Re: Need help with Tach

I found an older thread that Reeves had done and took the send wire from my tach to the yellow wire on my terminal strip and the tach worked great so I have determined that the rectifier is bad. So I am assuming that the rectifier side can go bad and the charging side can still operate ok. My rectifier also has a wire to my VRO2. Does anyone know what the recitifier has to do with the VRO2 pump?

 

[ezeke]

Re: Need help with Tach

One gray wire leads to the harness for the fuel pump; its part of the warning sytem. The pump is purely mechanical, only the alarm system is electronic.