Tacho problem, 1996 Johnson Oceanrunner 115HP.

If anyone can help me diagnose my problem I would be grateful.
I have had the outboard since new and had very few problems.
Towards the end of last season I noticed that when we were underway the tacho needle would drop to zero and then flick back up to the correct rpm (intermittently). It has gone through several different stages (see below) and now will only register idle speed and when the engine is accellerated drops to zero. when I return the throttle to idle it reads idle speed.

Other things I have noticed since the problem started:
1. Tacho needle drops to zero and then returns to the correct speed.
2. When I start the motor at sea the tacho would read idle speed and then as I accellerated the motor it would drop to zero and then some time later it would show the correct rpm (could be 1 minute or 5 minutes very irregular).
3. When we are underway and the tacho is reading say 4000 rpm and you trim the motor the tacho needle drops down to zero then returns to the correct speed when you stop using the trim switch.
4. Now it will only register idle speed and as soon as the engine is accellerated it drops to zero and stays there until you return the throttle to idle.

Thanks for any help.

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

Check to see if it is still charging the battery; if not then it's most likely the rectifier/regulator. Measure battery voltage with engine off; then check the voltage with engine running; if no change then that's what's doing it. Fried rectifier.

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

Thanks for your help. I will try it this weekend and let you know.

Ian

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

May be obvious but I had a loose wire that caused identical problem

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

I have had this on going problem with my tacho, please read above.
Anyway, thanks to you all I have tested to see if the motor is charging my battery and it is not.
Armed with this information and your help I ordered a new rectifyer for my motor.
I arrived just before Christmas but there is an obvious problem.
The Aluminium body is the same as the old unit and it all looks the same except that the old unit has 5 wires (1 x red, 1 x yellow, 1 x yellow/grey stripe, 1 x purple, 1 x grey).
The new part has 4 wires (1 x red, 1 x yellow, 1 x yellow/grey stripe, 1 x grey) it does not have the purple wire.
My question is: Is this a superseded part and I have to change some wires or is this the wrong part?
The part number on the new part is the same as the number on my old part except that the new part has a suffix (4111) the old part has no suffix number printed on it.
The microfishe that I ordered the part from shows the rectifyer with 5 wires the same as the original.
Any help would be appreciated.
Thanks,

Ian

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

The red wire is unswitched battery voltage from the Starter solenioid binding post. This wire charges your battery. The purple is switched battery voltage (ignition accessories) from the ign key. This wire was to sense the voltage and determine how much charging the battery needed.

Will the new regulator plug into the harness? if so, it is probably not an issue.

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

Had the same issue with my 1996, 175hp oceanrunner, after countless tests and almost at the brink of spending $150 for a rec/reg I discoverd a loose ground wire behind the starter motor. The ground wire lead directly to the rec/reg assembly. A good cleaning and adjustment took care of the problem.
H

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

Thanks for the information.
The plugs are identical to the old unit except no purple wire (still a double plug with only a grey wire, no purple).
I will check for a loose ground wire behind the starter first and then fit the new part.
If I understand this correctly, the purple wire controlled the charging of the battery? With no purple what will control the charging now?
Thanks for your help.

Ian

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

Ian, They use the red wire to sense the charging requirements.

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

is this a rectifier only charging system or is it a regulator?.....if it is a rectifier only then you are dealing with a known problem on those engines of that vintage....they will fail with a sealed or a gel battery.....the fix is to install a regulator(the mounting holes are already in the top of the engine) or to go with the manufactures recommended battery for the engine....even a non maintenance free battery will fail if it is too big....the original recommended size which i dont have the numbers for anymore is almost impossible to find...the first indication that you are getting into the danger zone is when the charging voltage gets to 16v or above...it may be 6 months or a year or the next trip but the rectifier is going to fail eventually...

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

the rectifier clear plastic filled covering wil usually melt and ooz if the recitfier has fried... I had one go on my 1995 115 ocean runner...I used the 1997 recitfier from my spare motor (also a 115 hp 60 degree looper)...i just cut the dusetch plug off and spliced it in....they changed plugs from 95 to 96.

I have since run the motor for 2 years with dual batteries , both deep cycles and large...with no issues.

bob

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

papyson, That unit is a water cooled voltage regulator with a 35 A capacity.

Re: Tacho problem, 1996 Johnson Oceanrunner 115HP.

Hi everyone,
Just wanted to let you know that with all your help I have been able to solve the problem with the tacho on my boat.
As you know I was a bit confused by the new rectifyer not having the Purple wire. In the end I phoned the manufacturers in Canada and got through to their technical help desk and before I had finished explaining that I had bought a new rectifyer and it was missing the purple wire the tech guy tells me "and it is missing a purple wire, right?". Seemingly the rectifyer is self energising now and doesn't require the purple wire.
So after reading all of your feed back I started by looking for a loose earth behind the starter motor. There is an earth wire attached to one of the starter bolts, and guess what, yes it was loose. I cleaned it up and started the motor. I was a bit relieved when the Tacho still did not work.
I pulled out the old rectifyer and could see a small bubble in the sealant that is on the top of the unit. I fitted the new unit and everything worked perfectly. Tacho working and alternator was charging 14.7 volts.
Thanks again for all your help, I couldn't have made the repair without it.

Regards,

Ian