Need help on a Johnson 90 (tach issue)

[gman 82 aquasport]

Sending out a "all call", Buddy of mine has a late 80's model 90 hp Johnson OB on his pontoon boat ..I was enticed  to rebuild his floor and install new seats and paint it for him over the winter. Got it all done in about 5 weeks, got it all rewired and running and find out the tach doesn't work, never has since he bought it 2 yrs ago...I fooled around with it for a couple of hours and got it to work and it worked for about 20 minutes then quit again...now it won't work at all ...It is powered off the ignition switch, bumps on when motor is cranked but not registering rpm's...have power to the gauge, light in gauge works, but no rpm...it was being fed by a small light blue wire out of the switch harness, my thinking is that this wire is faulty and I want to pull a new wire from the motor to the gauge direct..just looking for info on which wire to tap into to feed the tach and where is the best place to tap into it and not cause any other issues ...

And before anyone asks , I have no idea exactly what year as there are no markings on the motor...no decals were on it and we are assuming ( I know , dangerous) that it's the original motor to the boat which is a 1988 model..At least thats the info he got from the last owner :o Any help is greatly appreciated

[Georgie]

Gman-

Could also be the tach itself, the stator, or the rectifier/regulator.  Make sure you diagnose the problem for sure before you go through the trouble of replacing or modifying a wire in the original/intact harness.  The blue/gray wire runs from the connective strip on the starboard side of the engine to the big red electrical plug on the port side, and then from there it probably runs either to a wire harness plug in the console or all the way to the tach.  You'll need to check continuity across the length of this run before you assume it's bad (if you haven't already). The photo below shows the connective strip on the starboard side of the engine.  The yellow wire w/gray stripe wire coming from either the stator or rectifier/regulator on the top of the engine (cant' remember which off the top of my head) is attached to third connection down, and I'm pretty sure the gray wire it is bonded to is the one that runs all the way back to the tach.  If you can verify continuity from this point on the strip to the terminal on the back of your tachometer, then the wire is still good.   If no continuity, make sure you check each separate wire segment so you can replace just the segment that's failed. Also, if you can post photos of the carbs, midsection length, electrical system and gearcase I can help narrow down the year/model number a little bit.  If I think of anything else I'll let you know...  

[fitz73222]

Go Georgie Go!

Looks like my bench; powerhead and all! Good stuff, I love reading engine porn...

[Georgie]

That's the block in the 110 Johnson driving my fathers 170 now...he ran it a TON over the summer but hurricane Sandy did a number on his boat.  Gunwale, rubrail, trailer, helm, antenna, windshield all wrecked.  Approximately $2500 damage and his deductible is $2500.   :cry:  



Sorry for the mini-derail...

[gman 82 aquasport]

Thanks Georgie, It will probably be a couple of days before I get back to his shop and have time to check the wires you spoke of.. I will try and get a pic or 2 and post them up..I am trying to get my hands on a used tach that we know works to make sure that it's not the tach itself, then I'll check the wires...He's fine to not have it, but I keep telling him that the 2 gauges I wouldn't be without are the tach and temp(and volt) ..but  it's not my boat and I'm just trying to get it working so he can be more confident that it's running the way he wants it to..Outboards are still a little foreign to me and I'm still learning about them ...I'll post back after I get to test it ....This forum still rocks thanks to you guys who will answer ?....  

[dburr]

G when you are at the boat, take a look at the mount bracket,  and there you should find a data tag.. Grab all those numbers and a quick search with google (betcha the hit will be MarineEngine.com ) and you will have year and model series.  The parts are relatively universal but it is nice to know what you have

Edit: Try this
http://www.marineengine.com/manuals/johnson/#

[Capt. Bob]

Reading material from the CW Forum. This may help with tachometer operation understanding and show where Georgie's heading.
(Mod highlight/underline).

Typically, on traditional 2-stroke engines, the tach pulses are derived from the battery charging circuit and are just the raw, pulsating DC coming off the coil winding, ahead of the rectifier.

The rectifier does not make the pulses. In the typical configuration the rectifier is wired so that it provides the ground reference for the coil and also clamps the pulse amplitude at battery positive voltage.

When the rectifier fails, there are many possible failure modes. If it opens to ground, it may disable the tach. If it shorts the coil, it may disable the tach (and burn up the coil).

I had a bad rectifier on my old 1976 Merc 50-HP, but it had failed in such a way that the tachometer kept working just fine. The circuit that resulted was not doing any battery charging, but it made nice tach pulses.

The other component of the tach sender circuit is a coil, usually located under the flywheel. This is often called a stator, because it is stationary. Permanent magnets glued to the flywheel rotate above the coil and induce current flow in the coil when they pass over it.

The stator is subject to damage in several ways. Usually too much heat causes them harm. Since they are at the top of the engine and under the flywheel, they are in one of the hottest areas of the engine and not well ventilated. Heat from current flowing in them also builds up. If you are chronically in need of maximum charging current because of low battery voltage and high electrical load, the effect over time can be to overheat the stator coil.

Connecting the battery to the engine with the polarity reversed is another way to practically instantaneously damage the engine charging circuit. You will likely destroy the rectifier and possibly the stator coil if you have done this. It seems quite a common mistake.

If you can disconnect the stator coil leads from the rectifier, you can measure the resistance of the stator coil and check it for shorts to ground (if it is floating electrically, as they usually are).

You can also disconnect the rectifier and measure it, although on occassion a rectifier will measure as "good" but will fail in the real circuit. The failure may only occur with elevated temperature, for example.

The good news is that an OEM rectifier costs $35 (Mercury) or ($65 Yamaha---but of course those never fail, eh?). You can replace it in 5-minutes with simple tools.

The bad new is that a bad stator coil is more expensive, and much harder to replace. On some engines, the "stator" is part of a larger assembly that contains other coils. Sometimes these can be expensive. A friend with a MARINER engine (a Merc-Yamah hybrid) had to pay over $300 for a stator coil assembly. I have new stators on both my Yamaha engines and the coils only cost $90, in part because there are three different assemblies for coils under the stator and I only needed one of them. (And the one I needed was the cheapest, too!)

Even getting the part, there is still much work ahead to replace the stator. You have to remove the flywheel. From my experience with a little 70-HP Yamaha, it is impossible to remove the flywheel without the proper tools and an air-driven impact driver.

Once the flywheel is off, replacing the coil should be straightforward. When you put the engine back together you may need to retime the ignition pulses. That is probably more true if your stator coil assembly was an all-in-one unit which also had the ignition timing pulse coils in it.

Based on my experience, I would let a shop handle the flywheel removal, unless you happen to have the right tools lying around.

Take this method with a grain of salt(possibly different type system than what you're dealing with) but it too helps illustrate wiring connections and what they do (hopefully). From the iboats site.

Dave.... The following may be of interest to you.(Testing Tachometer With Water Cooled Regulator/Rectifier) A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.However.... those watercooled regulator/rectifiers that are used on the 35amp charging systems bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.Remove that gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.I've found this method to be a quick and efficent way offinding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disasterous consequences.

Wiring diagrams(very readable directly from the site) to choose from but a good service manual as noted above is worth its cost.


http://www.maxrules.com/JOwireindex.html

Good luck.

[Georgie]

find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

Excellent troubleshooting test, Bob.  Completely forgot about this trick!     So simple and yet really helps determine if either the stator or rectifier are at fault.

Sounds like; a) swapping the tach for a known good one, b) verifying continuity on the gray wire, and c) swapping the yellow wires during operation will in all likelihood find the faulty part.  I have quite a few used spare stators that I can offer if that turns out to be the problem.

[slvrlng]

Garry, I've got an used OMC tach if you want it.

[Capt. Bob]

Here's something else I stumbled across while searching out batteries.

http://www.cdielectronics.com/

Under Tech Support, some interesting troubleshooting guides for various motors using CDI ignitions.

Again,
Good luck.

[gman 82 aquasport]

Thanks Capt. Bob and Georgie, after reading those instructions I don't think even I can screw that test up... But it will be at least the end of next week before I am face to face with his boat again..Got the Mrs birthday this week and we are headed to the coast for 4 or 5 days...not getting to take "Therapy" with us as she has all the electronics out right now as I have been cleaning up my hurried wiring job from last year..plus I put in a washdown/livewell pump. I keep going back to pics of seabobs wiring , and try as I may, mine just doesn't quite look as good   but it is a lot neater than it was and everything has proper connections and is tied up..so I'm getting there
Lewis. I'll give you a pm if we decide to go the tach replacement route..Thanks

[Frank]

G     20 Apr

I lost my first attempt...had to relinquish laptop to wife's freind.

1.I was taught early on that a tach is a tool that can tell you two (2) things about your engine:
-Your prop choice is correct or incorrect, based on the rpm turned @ full throttle. Mot enough rpm...too much pitch. Too much rpm..not enough pitch, and a possible blown engine from over reving.
- Your charging system is operating (tach registers), or not operating (no tach reading when engine running.

2.Your problem is compounded by the fact that the tach 'never worked'. You may have a bad tach. I use a  working tach with alligator clipis to make sure I'm getting a signal to the tach from the engine.

3 I'd start out with a good repair manual for the make and model engine, preferably with a colored wiring diagram for the motor. Check the plate on the mounting bracket for the engine code & serial number.Also, many tacks have a switch on the back of the tach with numbers. Use a flat head screw driver to change the position to the number corresponding to the number of cylinders of your engine. Until the Etec motors, a 90HP was a V4 engine, and this info is for pre ETecs. The Etec 90 HP is a 3 cylinder motor, and I don't know if the wire colors remained the same.
 
4.Most OMC products use a purple wire for the tach lead, if memory servers. Some of the side mount control  boxes had a spot to plug in the tach.  Tachs are relatively inexpensive, with lots of good aftermarket or more expensive manufacturer's models available. Some used boat, motor dealers also sell parts,BUT make sure they demo the used tack for you BEFORE you leave the premises.Many of these guys tell you once you buy anything electrical, it's yours...NO RETURN. Good Luck! Let me know how things turned out, and if my info was accurate and helpful.

Frank

[dburr]

G     20 Apr
4.Most OMC products use a purple wire for the tach lead, if memory servers. Some of the side mount control  boxes had a spot to plug in the tach.  

A quick look at the OMC remote wire harness schematic shows the remote tach plug has grey purple and black wires.  A further look (Note: I am not wearing my glasses! ) appears that the purple is hot to the tach from the key, grey back to the stator and black to ground.

Hope this helps...

[Circle Hooked]

appears that the purple is hot to the tach from the key, grey back to the stator and black to ground.

I agree and so does my rigging guy, in letters from camp  

[gman 82 aquasport]

Thanks for all the help guys... We were finally able to get together for a day and check the tach issue out and it is a bad wire in the harness to the console..He is wanting to just wait till off season to fix it and since it's his boat, I will go along with that..I appreciate the info, it made finding the problem a lot easier, only took about 15 minutes to get to the bottom of it..