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Johnson 115hp/1984 how many pulses comes from tacho wire / rpm

T

timra

Member
Hi All,

Any one know how many pulses come from tacho wire / engine round ?

bought after market outboard rpm gauge and cant sync it to show correct rpm ?

Thanks.
 
1984 115hp Johnson emits six (6) pulses from the gray tachometer wire. Set the dial on the tachometer if so equipped to number six (6).
 
joereeves said:
1984 115hp Johnson emits six (6) pulses from the gray tachometer wire. Set the dial on the tachometer if so equipped to number six (6).
Click to expand...

Thanks for respond.

Have try setting 6 and tacho shows way too low rpm. It show only 3000 when reality is more near 4000-4500.
MAx setting is 10 and in setting 10 it shows way too high values.
Cant find any logic that gauge.
 
fdrgator said:
Do you have a voltage regulator on that engine?
Click to expand...

Thanks for respond.

Yes i think there are voltage regulator.

Tacho show now enough correct.

measureming tacho signal wire with multimeter Hz
value and setup tacho value. It is now 8.4.
100Hz is 1000rpm. I drive 30kmh multimeter shows 320Hz.
After that tune tacho to show 3200rpm when speed was same
30kmh. It is not 100% but it is enough for me.
 
The 1984 115hp Johnson, if factory equipped with PTT... it has a water cooled voltage regulator/rectifier located on top of the powerhead, directly to the rear of the flywheel. The model number of the engine would contain a "T" if so equipped.

Perhaps your present tachometer is not compatible or perhaps needs to be set differently, but at any rate... the pulse setting is definitely six (6).

What make is that tachometer? Did instructions come with it?
 
I confess I'm not familiar with the water cooled rectifier's tach pulses however some regulators control the voltage by interrupting the alternator's signal on one of the yellow wires. If you connect your tack to the wrong yellow wire you will get that interrupted signal and a false reading. Don't know if this helps or not.
 
Coinciding with "gators" latest post/reply... and if that tachometer is designed to function with a six (6) pulse alternator output, yes, you may very well have a regulator/rectifier malfunction interfering with the tachometers operation. See the following:
********************
(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.

Normally the Gray wire leading from the tachometer is attached at the terminal strip to another Gray wire which leads from the water cooled voltage regulator/rectifier...... remove the 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.
********************
 
Thanks for all respond’s

tacho is aftermarket universal boat engine model.
There is none fact that it will work with setting 6.

Frequency measurement looks to be correct and engine
gives correct 6 pulses / round.

my opinion is that aftermarket tacho is strange and engine
Work like it should.

Tacho is connect to remote control tacho plug.

Tacho works now with setting 8.4.

here is link to tacho doc (sorry no english).
https://www.biltema.fi/BiltemaDocuments/Manuals/25-8040_man.pdf
 
just need your help on another matter. i need the tool to be able to start the engine at the engine rather than having to go back and forth to the console to start and switch off the engine while trying to troubleshoot a problem
 
Don't know about today's stuff, but in bygone years every mechanic had a remote starter button in his toobox. Simply clips to the starter solenoid. Should have them at your local auto parts store.
 
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