1981 Johnson 90HP J90TLCIM rectifier issue?

[Bobobob]

I have recently purchased a boat, motor, trailer package with a 1981 Johnson 90HP J90TLCIM and I noticed that the Tach was hopping around all over the place and would often peg then drop to 0. I mentioned this to the local boat mechanic and he said it was a stator issue, and recommended replacing the rectifier. As it was the least expensive part of the system I figured it wouldn't hurt. I replaced it and wired it exactly the same as the old one. After this repair the Tach did exactly the same thing. I then decided to put on my big boy pants and get the manual out. I found the rectifier had been wired wrong. The yellow and yellow/grey wire had been reversed. I swapped these wires back to their correct location and now I have no Tach at all. Could I have damaged the rectifier by wiring it that way? Also what else could I be looking at if the rectifier is o.k.? my Clymer manual doesn't seem to go into this area. I'll add a link to a picture of the wiring.

wiring-rectifier by rparent2014, on Flickr

 

[Bobobob]

here it is with the cover

CAM00425 by rparent2014, on Flickr

 

[Snoopy-2]

There are two things that will blow a rectifier. One is connecting the battery with the polarity reversed. Even briefly ... instant death!
The other is disconnecting the battery while the engine is running.
You might get away with it at idle speed when the current is low but otherwise it is likely to cause a voltage surge which will blow the diodes.

 

[Bobobob]

Well I guess the next question is; what's up with my tach. anyone have any ideas? or any insight as to where to start?

 

[Bobobob]

So the local boat mechanic says the Tach uses the stator pulses to show the RPM, if the rectifier is good and wired right, how likely is it that the voltage regulator could be causing an issue? I'm at a little bit of a loss here, like I said before my manual doesn't really talk about Tach signals or such.

Any help would be great.

 

[Derekxj]

Ive got this same exact thing going on on my 85' 140. Hooked up a brand new tach, and its bouncing all over the place at an idle.
Then when i go to rev the engine a little bit it instantly pins itself down to 0 and when it returns to idle, it begins bouncing around again.

Very strange. I was going to start with my rectifier, or heck just change both rectifier and stator.

 

[Derekxj]

So the local boat mechanic says the Tach uses the stator pulses to show the RPM, if the rectifier is good and wired right, how likely is it that the voltage regulator could be causing an issue? I'm at a little bit of a loss here, like I said before my manual doesn't really talk about Tach signals or such.

Any help would be great.

Any updates on this?? Im about to order a new rectifier AND stator simply due to lack of knowledge. I'd hate throwing good money after bad
and changing both just because i simply dont know better. I do however really need to get this thing going so i can enjoy my boat! lol.

 

[emdsapmgr]

I'd hold off on the purchase of the stator till you see what happens when the new rectifier is installed. The rectifier is cheap, compared to the stator.

 

[Nitro2014]

I am having the same issue. I took it to the local boat mechanic and after he tested the charging system, he said that it was a faulty rectifier/regulator. (Figured it was better to spend the money finding the problem rather than just replacing parts hoping one will work. A water cooled rectifier, stator, and tachometer can get very expensive and it could be something as simple as a wiring issue. You might do some testing before replacing parts as it may save you a lot of money in the long run. Good luck!

 

[Derekxj]

Thanks guys. Im going to replace the rectifier. I had an issue with my battery discharging as well. When this happened i started the engine with my truck battery, then switched the terminals over to the other battery while running to get charge into the boat battery. I've heard this alone can kill a rectifier and is a no no.

Now i have a bad coil pack. Im going to order the rectifier
and the coil pack today and go from there.

 

[Bobobob]

Well, I tried a new Rectifier, that didn't resolve the issue, installed a new voltage regulator, that didn't resolve the issue, Tested the stator windings as per the Clymer shop manual, and it tests out o.k. I'm no further along then I was before, the Tach just bobs around, then flatlines, then pops back up again. Anyone have any other ideas?

 

[emdsapmgr]

So the next question is-does the engine charge the battery? What voltage do you see at the battery after the engine has been running for 20 minutes at average rpm's? Put a typical voltmeter on the battery when running. Is the voltage normal battery voltage (12.5 or 12.6) or does it go up to 13.5 volts?

 

[Bobobob]

Seems to be around 12.65 Volts at idle, looks like it's not charging. well at least not all the time. So if I have a new Rectifier, and Regulator, must be the stator right?