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Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts missing

rjrobin2002

New member
My boat will run great for about 10 minutes in all RPM's, then it will only idle after getting warmed up and the idle is ruff. I checked the voltage coming from the red rectifier wire with the boat just cranked and I got a 14.8 volt reading at idle. After about 10 minutes it starts running bad and I now have only 4 volts coming from the rectifier. So I have a ignition and charging problem that starts about 10 minutes after the boat is running. Any suggestions. I pulled the flywheet and everythind looks good. I am fixing to start testing stator, rectifiers and coils. Just was looking for some sugestions. Any help would be appreciated.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

Sorry about that, it is a 91 Johnson 40 hp, model number J40TLCEC. I checked the AC voltage from the stator today with from what I have read I needed 18-24 volts AC. I have 6 volts at idle and it would max out at about 17 volts when reved up. When it gets warmed up it will not rev up at all and my stator volts are about 6 AC max and my rectifier volts are about 4 volts DC. So I am not charging and I my engine is missing when this drop in volts occur. I checked all my wire for shorts and my magnets on my flywheel are solid. No signs of anything burnt on stator, coils, rectifiers. I ohm checked the rectifier and it checked out OK.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

I think you need a special meter to read the a/c volts on a stator. Based on your symptoms I would have suspected the stator.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

The stator does two things. It generates power to charge the battery, and it generates power to run the ignition (via the powerpack). I'm wondering if it is shorted, overheating, and going south when it gets hot. Keep in mind, I'm no pro, & these are just my thoughts. IMHO, rectifiers are either open, shorted, or OK. I never heard of one that shorts when it gets hot, then works when it cools. But I do think a stator is capable of that.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

When I pulled the flywheel and when looking up parts, there is a ignition module, stator, and a coil on my timing assemble. The coil pluged into the ignition module and I thought it generated the electricity for the ignition, while the stator generated it for the rectifier and battery. This is my first outboard to work on so I am not good at this at all.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

the stator supplies all the power for the motor and for charging system.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

What does the "coil+lamination" as the parts catalog calls it do? Is is plugged into the ignition module.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

The "coil and lamination" is the coil that powers the ignition system

The stator assembly are the coils that generate the power for battery charging via the rectifier.

(Some motors have the two combined into one unit)

BTW
J40TLCEC is the model number for a 1989 model not 1991

You can check the AC volts going to the rectifier with an ordinary AC voltmeter
It is a four wire rectifier ? ?

Between the yellow and the yellow/gray wires you should get something that rises well above 12volts, to 18 or something like that as you rev the engine. Likewise between the Yellow/blue and the yellow/gray. I dont know what you'll get between yellow and yellow/blue.

You can test the continuity of the stator coils, if you disconnect it, with an ohns meter. you should get a low reading between any of the wires but the reading between Yellow and yellow/blue will be double the other readings.

You can test the round three and four wire rectifiers by following Joe Reeves' instructions

Perhaps your engine does not have the water cooled regulator/rectifer but rather incorporates the smaller 3 wire rectifier which sits just forward of a vertical electrical strip on the starboard side of the engine.

If so, a failed rectifier would knock out the tachometer. See the following.



Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.

Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.

Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.

Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.​

But if you use a digital meter use it on the "Diode test" setting not an ohms range. If you have no diode test setting the use the highest ohms range.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

It is a 4 wire rectifier and I did the OHMS checks on it using Joe Reeves method and it checked out OK. My stator volts are 6 AC between the wires you mentioned and when these are low I have an ignition problem also. When it is running good, I get 6 volts at idle and it maxs at 17 volts. No one has a reason why these would happen together? I figured this happen frequently.
 
Re: Rectifier volts drop from 14-4volts after 10 minutes of idle, then it starts miss

I got a complete timer base, ignition coil, ignition module and stator used from Ebay and installed it today. Dont know which electrical component was the problem, but my problem is fixed. I drove the heck out of it for an hour or so and it ran great. $90 fix.
 
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