tach

[mickey117]

tach doesn't seem to work.although when starting motor needle seems to move ever so slightly,but when started tach shows nothing.any clues on how to check before getting a new one.

 

[Joe Reeves]

Re: tach

The procedure depends on what engine you have. What is the model number?

 

[mickey117]

Re: tach

it's a 90 hp evinrude omc (1986) not sure of model but the back of the tach has 4 wires coming from back.( no poles )

 

[rickdb1boat]

Re: tach

Make sure your charging system is working. The tach will not function if it isn't. Take a voltage reading with the engine off. Then again with it running at fast idle. You should see an increase if it's working...

 

[mickey117]

Re: tach

I tried testing to see if charging system was ok placed meter on battery got 12.57 at idle. sped it up and got an got 12.68 something like that.my question is was that a big enough jump to say charging system is ok

 

[Joe Reeves]

Re: tach

(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 watercooled regulator/rectifiers that are used on the 35amp 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.

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 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 disasterous consequences.

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store

 

[mickey117]

Re: tach

looked for grey wire at term.strip only see one gray which is connected to a yell/grey wire via jumper.yell/grey goes to rectifier

 

[Joe Reeves]

Re: tach

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.

(Small Rectifier Test)
(J. Reeves)

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.

 

[mickey117]

Re: tach

well ohm out rectifier seemed to be good .i say seemed cause it ohm out w/red touching body of rectifier then no reading w/black on rectifier anyway i got a reading one way not other.then replaced tach started up motor once again tach not working.I guess I'll replace rectifier and see what happens thanx for everything

 

[ezeke]

Re: tach

Before you replace parts, try disconnecting the gray wire at the engine's terminal block and running a temporary pulse wire to the tach. Be a shame to replace parts if it is just a bad wire. A little corrosion in the harness plug can give the same problem.

 

[mickey117]

Re: tach

tried the temp wire,got the same result.so I know it's not the tach ,not the rectifier (ohmed out ok). anyway it could be the stator? when i ohmed out stator got reading of .7 checked manual it's says it should be .6-.6.4.Is .7 ok?I also tried removing ground off battery with motor running to see if motor would die. motor kept running does this mean the stator is ok?

 

[Joe Reeves]

Re: tach

Don't ever disconnect a battery from a running engine as that usually results in having the rectifier fail. Run the above ohm test on that rectifier again to be sure you didn't damage it.

The ignition on that engine is self contained, meaning it does not rely on battery voltage to energize the ignition.

As Zeke states.... Run a seperate wire from the gray terminal lead at the wiring terminal strip on the engine to the sensor lead at the tachometer to make sure the gray wire isn't faulty. The above sounds like you may have already done that but it's worth double checking.

Connect a voltage meter across the battery posts and jot down the reading you see. Now, start the engine and view the voltage there. If the voltage increases, then obviously the stator and the charging system in general is okay.

If the charging system checks out as above, and the rectifier is okay, and all the wiring is as it should be, unfortunately that leaves the tachometer.

 

[mickey117]

Re: tach

did the battery test.with boat at idle meter read 12.51 reved motor up for a little bit meter read 12.76.is this enough increase to say that charging system is working ok?

 

[Joe Reeves]

Re: tach

That would indicate that the charging system is functioning.

However, you want to have the volt meter connected across ther battery and jot down the reading with the engine NOT RUNNING..... then start and run the engine to take the other reading.

What is the voltage difference there?

 

[makorazor]

Re: tach

WOW 30 YEARS!! Ive struck the mother load! This maybe slightly off topic but I think Im having rectifier problems as well. And you mentioned that the ignition system is not powered by the battery power. I believe this maybe why Im having weak spark issues (its got enough to give ya a good zap but not enough to fire). Im going to give your test a go tomarrow and see what I come up with but Im also wondering if it could be a regulator problem. I have the Old 115 johnson with (non watercooled) separate rectifier / regulator. Do you know of a good test for the regulator as well?

Thanks for the great tips!!

Jason Woods

 

[ezeke]

Re: tach

Jason, it will help everyone and you if you start your own thread.

8)

 

[makorazor]

Re: tach

Will do,

Sorry NEWBIE mistake,

Jasond

 

[mickey117]

Re: tach

tested battery today and beleive the stator it to be ok.already ordered rectifier will see if it does the trick tomorrow .thanks for everyones help

 

[mickey117]

Re: tach

rectifier did the trick .thanks everyone for all the help,could of never did it w/out yous.