Analog Tach

[AGENT 37]

I've got a Yamaha analog tach in the boat now that I believe is malfunctioning. It operates smoothly and is accurate at low throttle settings but when I get up over 3500 it gets erratic and when I put in 3/4 throttle it shoots up over 7000 and dances around. Pole settings are right. I tried different positions and it acts the same except for the obvious difference in RPMs obtained by changing the pole setting. I rigged in a generic faria outboard tach and only the back light would work on it; no RPM indication. I'm assuming that tach is bad. Anything else to check before I go buy a new tach? All connections are good and clean.

 

[rodbolt]

Re: Analog Tach

you may wish to check the rectifier and stator output voltages.
but not knowing anything other than its a yamaha its all the advice I can give

 

[AGENT 37]

Re: Analog Tach

How much more info could you give me if I told you that it's my 99 F100? It seems like the needle bounces with the motion of the boat. But on flat water it still is erratic. Check green tach signal wire to a common ground? Do you have a better procedure to check it from the RECT? What min/max voltage should I get? I assume that if I get a smooth indication at the motor that generation side is OK and should rig a known good tach to see what happens.

 

[rodbolt]

Re: Analog Tach

let me check my notes during the week, its not published but I do have some stuff written down.
most yamaha stuff is taken off the rectifier but some are generated by the ECU based on pulser or crank position sensors.

 

[AGENT 37]

Re: Analog Tach

Have you looked through your notes lately?

 

[rodbolt]

Re: Analog Tach

nope, but I remember some yamaha ECUs develop the tach signal and some dont.
but keep bumping this and I will remember to look.
but in any case its going to be a linear tach signal.
look at the tach input voltage, it should rise and fall steady.