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Author Topic:   Intermittent Tachometer: Evinrude 225
davidestel posted 01-08-2006 09:54 AM ET (US)   Profile for davidestel   Send Email to davidestel  
I tested my 225-HP Evinrude motor, 1998 model E225CX. The engine starts and runs perfectly. After 5 minutes at 1,200-RPM [fast warm up speed] the engine idle speed decreases to 800-RPM [the normal idle speed]. Everything perfect! But after two minutes the tachometer stops working and sometimes jumps. I have tried another one and the story is the same. It works only few minutes when cold, then nothing. Any idea? How can I test the rectifier?
seahorse posted 01-08-2006 10:21 AM ET (US)     Profile for seahorse  Send Email to seahorse     
The regulator has an internal circuit that generates the tach signal, and it is tested by using a peak reading voltmeter or a DVA adapter with a digital meter. IT is explained in the service manual.

What is the model number of your motor as there were some "fixes" on the '93 to '97 models to extend regulator life.

Do you have wing nuts on the battery terminals or the required lockwashers and hex nuts tightened with a wrench?

A quick output check is to crank the motor over for about 20 seconds, but not starting it. Then fire it up with a 40 amp or greater ammeter in line with the red regulator wire. If the charging system is good, it will put out about 35 amps above 2000 rpm. You still could have a bad tach circuit in the regulator, but that is rare if the rest of the system is OK.

Look up under the flywheel and see if the black insulated coils on the stator assembly are dripping black goo. If so, replace that also as it is a result of loose battery cables and the resulting regulator damage.

jimh posted 01-08-2006 01:04 PM ET (US)     Profile for jimh  Send Email to jimh     
The tachometer signal is developed in the Voltage Regulator assembly. Unfortunately this assembly is a rather expensive replacement part, about $230 (U.S. funds). The assembly is mounted into an access hole in the engine block where it is designed to receive cooling water. The assembly consists of a large heat sink block with an encapsulated circuit board.

You have to remove the Power Pack assembly (it looks like a cover plate) to access the Voltage Regulator assembly. You may be able to see the greenish encapsulating material. The circuit board and other components are embedded inside the assembly and are not serviceable. I tried to dig the circuit board out of my old regulator. It was quite difficult. I would consider it to be a non-repairable item. If the assembly has been overheated, the potting material tends to harden and crystalize, which makes it more difficult to remove if you were going to try to repair to the component level.

The tachometer signal is also a derivative signal from the main battery charging coils in the stator assembly. If the battery charging coils have been damaged this will also affect the tachometer.

It may very well be the case in your motor that there is also a problem with the battery charging circuit. The presence of an erratic tachometer signal may be an indicator of more problems with the stator coil and voltage regulator assembly.

The stator coil is also somewhat expensive. I think they are about $150 (U.S. funds). The problem with a stator coil replacement is its location under the flywheel. The flywheel must be removed to replace the stator coils. This can be difficult to accomplish because of the high torque needed to remove the flywheel retaining nut. You may also need a special wrench to retain the flywheel itself. Sometimes a strap wrench can be used.

Even with the flywheel in place, you can make a close visual inspection of the stator coil (as Seahorse suggests). You can probably see evidence of overheating if it was severe. You can also check the continuity of the stator coil.

Because the problem occurs when the engine has warmed up, it could very well be an intermittent component in the Voltage Regulator assembly or a problem in the stator coil which occurs when it heats up.

As seahorse mentioned, loose battery connections may be the underlying cause of these problems. Also, chronic low battery voltage and heavy charging currents can also cause a high load on the charging circuit in the motor. This in turn will cause it to be operating with a much higher temperature, leading to shorter life span.

Also, low water pressure and lack of cooling water to the Voltage Regulator assembly can cause higher temperature operation. Check the cooling system for good water pressure.

davidestel posted 01-08-2006 04:28 PM ET (US)     Profile for davidestel  Send Email to davidestel     
Thanks Jim. After your reply I can check only the cooling system (7 pm in Italy) and I discover that only a poor quantity of water comes out from the upper hole system. The pressure gauge says about 10/12 PSI at the minimun rpm during the warming up. Temperature gauges on Board and Starboard are at about 110/120° F. Maybe the regulator is overheating. I notice that when the cowl is open the Tachometer works for few minutes at cold and sometimes jump at warm if I turn off the engine for few seconds and then retry to start the tachs work for another few minutes (1-2),instead when the cowl is closed the gauge works until the engine is cold then stop, restart to work only after several minutes of pause.
Outside here is about 6-8°C.

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