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Re: 3126B marine engine serial@ 3GS00302 intermittent tach

I have the exact same symptom so will watch your responses.
Changed alternator, heater relay, circuit breaker. No change.
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Re: 3126B marine engine serial@ 3GS00302 intermittent tach

My engine is using the ECM to drive the tachometer. As i said before, when I start it the tach stays at zero and the alarm light remains on and I get intermittent beeps. This is the same sound I hear if I just simple turn the ignition on.

ON occasion, the tach will begin to work, mostly at around 1800-2000 RPM,. thIs is not a regular occurance nor does it always start to work at 1800RPM. its very sometimeish.

Also, the tach in the salon will sometimes start to work and the one on the bridge will remain at zero and the alarm will continue. Sometime during the day both tachs will begin to work normally and the alarm light will go out and the beeps will stop. An indication that the tach will begin working is by a very high frequency blink of my alarm light and a sound of a small relay buzzing at the same rate.

Once I reduce engine speed to idle, one or both tachs will cease to operate and the alarm light and buzzer will come on.

It would seem that at this time there is no charge voltage going to my battery.

I have replaced my alternator with a new one and this has not solved the problem. I did this because I beleive that there is a pulse signal from the alternator to the ECM. (I only think so, but Im not sure of this because I do not have a wiring diagram)

I presume that the Tach gets its input from the ecm that in turn the ECM gets its pulse input from the alternator.

 

Can you advise a troubleshooting method I can use to determin if I have a wiring problem or if my ECM is acting up?

Any advise  would be greatly appreciated.

 

 

 

Super Contributor

Re: 3126B marine engine serial@ 3GS00302 intermittent tach

Your original post sounds like the tachometer is being driven by the alternator instead of a separate mag pickup. The easiest way is to use the engine ECM. PPR is "pulses per revolution".
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Re: 3126B marine engine serial@ 3GS00302 intermittent tach

Also, not sure what you mean by PPR or 126 and 134

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Re: 3126B marine engine serial@ 3GS00302 intermittent tach

Dave, I am assuming that is how it is hooked up already. I needed the pinouts to physially check the wires. Thanks for the info. I will have a look and see what is the condition of the wires at these pins on the ECM jack and trace them back to the tach. Hopefully I will find the problem. Thanks again.

Super Contributor

Re: 3126B marine engine serial@ 3GS00302 intermittent tach

Why not use the engine ECM tachometer output to drive the tachometer? Pins 14 and 15 at the 40-pin customer connector.. Tachometer needs to have the ability to adjust the PPR to either 126 or 134.
Contributor

3126B marine engine serial@ 3GS00302 intermittent tach

[ Edited ]

Hello experts, Can I get a wiring diagram to help me trouble shoot an intermittent tach signal to one and sometimes both my tachs.

The engine will start normally and the ignition buzzer will remain on and the tach reads zero. on occassion the tach in the salon will begin to work and the buzzer will stay on, while the tach on the bridge will stay at zero. Other times both tachs will begin to work and the buzzer will turn off. Very intermittent. Once the both tachs are operational and I bring the trottles down to idle, the tachs will drop off and the buzzer will come back on. I have already replaced my alternator with a new one and this has not solved the problem. The tachs will work sometimes as soon as I start or sometimes when I increase trottle but not in any regular sequence. Thanks in advance.. Also, it does not seem to be sending charge to my battery when the tach is not working.