1994 Mercury 115 HP RPM Read out problems

[Jose Almeraz]

Any body, what could be the cause I am not getting a signal to the RPM gauge? What are some of the things I can check to solve this problem?

 

[Laddies]

Re: 1994 Mercury 115 HP RPM Read out problems

Thre is a good chance the rectifier is shorted out take the grey wire off the yellow post it's on and move it to the other one, if it works then it's the rectifier.

 

[pops]

Re: 1994 Mercury 115 HP RPM Read out problems

Laddies, or anyone, please clarify previous post.

Move wire to other yellow post????? Do you get needle movement with switch on?, needle movement with motor not running?

Am I looking for an ohms reading on the tach wire?, or an actual tach reading with motor running?

What can I fry if I do this wrong?

 

[pops]

Re: 1994 Mercury 115 HP RPM Read out problems

Moving this thread to todays posts for possible reply.

 

[Chris1956]

Re: 1994 Mercury 115 HP RPM Read out problems

Pops, The rectifier has two yellow wires that carry AC, and either will serve to provide the Tach with the necessary signal. If one side of the rectifier is shorted, no signal will be generated to run the tach.

BTW- when power is applied to the tach, motor not running, the tach should zero.

 

[Jose Almeraz]

Re: 1994 Mercury 115 HP RPM Read out problems

I've been away and finally got back into town. I'm still a little confused on how to connect the wires to check the rectifier. My rectifier has 2 reds, 2 yellows, and 1 grey. Can you explain which wires to disconnect and connect?

 

[j_martin]

Re: 1994 Mercury 115 HP RPM Read out problems

It's not a rectifier. It's a voltage regulator, and the tach signal is taken from the stator internal to it.

First, check the battery voltage. It should be above 12 v shut off, and noticably higher, usually over 14 v when running, (and maybe revved up a bit) Don't run it at all without water, even for a short test.

If the battery voltage is low when running, replace the regulator.
If it goes up, then further testing is needed to determine if it's the regulator or the tach.

hope it helps
John.

 

[pops]

Re: 1994 Mercury 115 HP RPM Read out problems

Jose, J. is right. I had no tach reading and starting battery was getting low after two or three trips to lake (it was not being recharged by motor).

I replaced REGULATOR (two red wires, two yellow wires, and grey wire coming out of potted box) with aftermarket CDI unit and now everything works. Tach reads correctly, and starting battery now shows 14 volts on simple volt meter running down the lake.

There is a rectifier on R. side of your motor with two yellow wires and one grey one. It is usually a non issue for the mid 90's 115 HP motor having tach/charging problems.

 

[Jose Almeraz]

Re: 1994 Mercury 115 HP RPM Read out problems

Thanks for the clarification. Is there a reliable aftermarket supplier and a brand name you use?

 

[pops]

Re: 1994 Mercury 115 HP RPM Read out problems

As mentioned in my post, CDI is the (best) aftermarket supplier. You can look up the proper replacement part on the net.

If your regulator is original equipment, just take it loose from the motor and look at clear potting on the bottom side. Chances are that the clear potting will show a large burned area on the circuit board. This is further confirmation that the unit is bad.

 

[Jose Almeraz]

Re: 1994 Mercury 115 HP RPM Read out problems

Pops, I performed the checks as you stated and they checked out good. Battery not running read 12.4V and running went as high as 13.8V. Thinking about it, I've used the boat several times and never charged the battery. Now that the regulator checked good, what would be the next thing to check, the rectifier or tach? How would I perform the checks if need be?

 

[j_martin]

Re: 1994 Mercury 115 HP RPM Read out problems

I'll jump in here. Try tapping the tach wire into either of the yellow wires that come from the stator. (get crimp on bullet connectors at your local hardware store or auto parts store)

If it works, the regulator is bad. (not likely) If it doesn't work, the tach is bad.

While you're at it, check for continuity in the tachometer wire. It goes through several connectors, each of which could be a pitfall for the signal.

hope it helps
John

 

[j_martin]

Re: 1994 Mercury 115 HP RPM Read out problems

Just thought of an easier way. There should be a 12 volt or so ac voltage at the tachometer signal terminal. If it's 0, or real low, the wiring and reg are suspect. If it's pretty strong, the tach is bad.

hope it helps
John

 

[Jose Almeraz]

Re: 1994 Mercury 115 HP RPM Read out problems

J, On what wires do I check for the voltage. I know there are several connections on the tach. My tach has 4 connections, LT, GRND, IGN, and SEND. I tested the following way.

With the ignition key OFF: Voltmeter black to GND and red to IGN got no voltage. Then black to GND and red to SEND got 10.8V.

With the ignition ON: Voltmeter black to GRND and red to IGN got 12.36V. Then black to GND and red to SEND got 10.05V. By the way the tach is at 3 rpm and when I turn the key it zero's out. Any opinions?

 

[Jose Almeraz]

Re: 1994 Mercury 115 HP RPM Read out problems

Moving this thread to today for any possible responses from any one. Help!!!!

 

[pops]

Re: 1994 Mercury 115 HP RPM Read out problems

J, based on what you found, I would vote for tach being bad. I think the reading with power off is very suspect.

 

[richw46]

Re: 1994 Mercury 115 HP RPM Read out problems

I wonder if I can wake up this thread again.

My '95 115 Merc's tach has stopped working. Reading through this thread and others I have tried several things, including the Teleflex instructions at http://www.downloadingfiles.co.uk/teleflexfiles/gauges/A Basic Gauge Test.pdf

I've not run any tests with the motor started but the readings I'm getting with the engine off are:
Switch off:
gnd to ign = 0 volt
gnd to snd = 1 volt (constant, coming from snd wire)

Switch on:
gnd to ign = 12+ volts
gnd to snd = 1 volt (constant, coming from snd wire)

Teleflex site said disconnect send wire and turn ignition on, needle should move to max. (I got no movement) Put jumper between gnd and snd and turn on ignition and needle should stay at / drop to 0. (I did this and I didn't get any movement)

I find it odd that the snd wire is sending a constant 1 volt, regardless of the switch position. Could this be a battery drain??? Is it normal???

Rich

 

[richw46]

Re: 1994 Mercury 115 HP RPM Read out problems

I dragged it out to the driveway and put the muffs on it, cranked it up. Here is more information

Switch on, motor running:
13.8 volts on the 2 fish finders at idle
16.8 volts on the 2 fish finders at fast idle
gnd to snd = 2 volts AC (constant, coming from snd wire)

Voltage through the snd wire to the tach is constant. There is no change if I go from a slow idle to a fast idle. Tach needle is at zero, it never moves.

So it appears to be charging but nothing is coming down the snd wire. Looking up the regulator on this site in the parts area I see its a rectifier and regulator combined. (2 red, 2 yellow, 1 gray) Is it possible that the rectifier is bad but the regulator is good?