Merc 115 2+2 RPM Gauge

[Superjetjim]

Hi,

My RPM counter doesn’t work on a boat I recently purchased with a Merc 115 - can I simply check for voltage on a wire on the back of the gauge perhaps, or is it more complex than that?

Also - is my engine a 93 looking at the serial number 09776985?

Thanks for any help!

Jim

 

[GA_Boater]

Is the battery charging? If not a duff rectifier/regulator or stator can cause a non-working tach.

 

[Superjetjim]

OK Thanks GA, so am I looking for around 14v at the battery when running (rather than say 12v when off)?
Its a new boat to me (not been in the water yet so not sure if charging yet, but can test on the hose / test tank.

 

[Superjetjim]

How would I age the motor using S/N 09776985?

i think it’s a 93, but not 100% sure.

Thanks again

 

[Superjetjim]

So thanks for the advice above - I had the boat out today for a good run. The RPM gauge ‘twitches’ when you switch the ignition on, but doesn’t display any RPM or move again after that.
Battery voltage readings are:
Motor off (after a good run) 13.4v
Motor running at idle 14.14v

What’s the likely culprit then, regulator/rectified or RPM gauge??

First run out in her today, they idle so smoothly these 2+2’s, I was actually quite impressed. Bags of power out the hole as well.

Thanks,

Jim

 

[jimmbo]

I think it is either the gauge, or a bad wire/connection to it

However, what voltage reading are you getting at WOT?

 

[Superjetjim]

Not taken a WOT reading

 

[Superjetjim]

How would I test if it’s the wire from the motor to the gauge? Is it just a case of running another grey wire from the motor to the back of the tach?

 

[Superjetjim]

Any help gratefully received

 

[GA_Boater]

How would I test if it’s the wire from the motor to the gauge? Is it just a case of running another grey wire from the motor to the back of the tach?

Blue, purple, fucshia, puce - Any wire color will work to test the tach. Just hook it up to the motor and run it to the tach as a temporary test.