Stator - Tach failure

[Incorrigible]

Engine: J225TXESS (1990 225hp)

Have run diagnostics on stator which indicate the output is less than called for. Output is below the 130 volts minimum.

The tach on this engine only reads to approx 2000 rpms and then returns to zero after the engine RPMs increase.

Additionally, this engine will start to misfire at (guessing, no tach) 3500 or so RPM's. Having gone over the fuel system, and regapping the plugs, checking compression, testing SLOW ops, I'm curious:

Does the stator charge the battery (I believe so) AND ALSO provide the current for the coils (I believe????) If so, is there a possibility that the failing stator could be causing the engine to miss at higher RPM's due to the higher demand of the six ignition coils?

As well, could a failing stator be a source of the problem for the tach at higher rpms?

Thanks

 

[Joe Reeves]

Re: Stator - Tach failure

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

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 water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) 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.

NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.

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 efficient way of finding 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 disastrous consequences.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1

 

[Incorrigible]

Re: Stator - Tach failure

Tach is new (of course, that doesn't mean it has not failed) Will test as described:

If the rectifier/regulator is faulty, would this impact the resistence and output measurements of the stator?

 

[Joe Reeves]

Re: Stator - Tach failure

Those output measurements are taken with the stator disconnected..... the volt regulator/rectifier is out of the circuit.

 

[Incorrigible]

Re: Stator - Tach failure

UPDATE:

Connected starboard engine to port engine tach (port engine tach performs properly with port engine)

No reading.

Connected gray tach wire as per instructions above. NO READING on EITHER tach.

All tests performed point to faulty rectifier/regulator.

HOWERVER: Based on the information above: The test results would indicate that BOTH of my tachs have failed. (ie I moved the gray wire, and this did not send a signal to either tachs, one that I have yet to verify is operational, one that I KNOW is operational)

I will test the starboard tach with the port engine over the weekend and post results. Will be replacing starboard rectifier/regulator

It is WORTH mentioning: I did NOT try connecting the gray wire to the YELLOW wire, only the yellow/gray wire.

 

[Incorrigible]

Re: Stator - Tach failure

Forgot to update this:

Ran all tests per the manual, indicating failure of the rectifier/regulator.

Installed new r/r. All is well!!!