Stalling, sudden low idle.

[ESGWheel]

Survivor, if you are not familiar > the reason for targeting the tachometer is that its ultimately hooked into the negative side (triggering side) of the coil. If the tach is shorting out intermittently it could easily cause the coil to not spark intermittently. By removing it from the ign. circuit and if all is now good, issue is the tach. Tachs, in a marine environment, are susceptible to internal corrosion and thus shorting out.

 

[Lou C]

That's probably one of the most sneaky causes of a misfire, that you could ever have, like a frayed wire from the coil to the distributor.....

 

[ShoalSurvivor]

I see no mention of a faulty tachometer. If the tachometer is going south it will also cause running issues. If it acts up again, disconnect it and see if it runs well.

Will do. Curious, though. Is there signal from the tach back to the engine, or is there an electrical change that the engine responds to?

 

[Scott06]

Will do. Curious, though. Is there signal from the tach back to the engine, or is there an electrical change that the engine responds to?

negative side of coil sends signal to tach. Some mercs will have two grey wires on negative side of coil- one for tach one for ignition module. You can take off the one going to the the tach.

Others will have only one wire that splits in the harness and and goes to Ignition module and tach, in this case remove the signal wire from back of tach and tape off to test.

 

[Bondo]

Will do. Curious, though. Is there signal from the tach back to the engine, or is there an electrical change that the engine responds to?

Ayuh,.... A failing tach, can ground out the coil, causing the motor to quit,....