Johnson 175 HP Tachometer Fluctuation

[Edward F. Alexander Jr.]

" I am experiencing indication

" I am experiencing indications on my boat tachometer that I am trying to correct. Most of the time while at full throttle, my Tachometer reads 5400-5500, but occasionally it starts popping back and forth anywhere between 4500 and 5500 with no noticeable difference in boat motor performance. On occassion, I get no reading with the motor running. It seems as though something is loose, defective or there is a bad connection in the circuit and devices that make up the Tachometer readings. I have looked for some troubleshooting info on the OMC setup I have, but can't find any. Please Help!! "

 

[sal]

" Sounds like your regulator/

" Sounds like your regulator/ rectitier is on its way out.This is a common symptom/telltale sign. Had the same problem on my 140 hp rude- replaced the part and now ok. Also, check the wiring harness by your throttle.Make sure the pins are clean and the the connection is secure. The part (in my case) ran close to $80.00. Not a big job if you have enough clearance(flywheel). Hope I was able to help. "

 

[bubba]

" There are several tests for

" There are several tests for the rectifier, but the simplest is with a volt meter, get your battery voltage without the motor running (should be about 12.6 Volts-DC) then start up the motor and check your battery voltage. You should get a 1.5 to 2.5 volt bump at idle speed if your charging system is working. Almost always, if your charging system is working, the rectifier is fine and should drive your tachometer. If you have an older 175 (older than 1985), you may not have a voltage regulator on your charging system and your tachometer is dropping out at high speed from very high voltage (usually over 16.5 volts). The easy fix is to make a shunt from a 2K resister from Radio Shack. Connect the resister between the ground and pulse (or sender) poles on the back of your tachometer. Happy boating. "