bouncing tachometer

[skiMachine]

First trip out this year, and the boat ran well except for one thing: <br /><br />the tachometer bounced wildly between 1000-3000 with no audible change in engine. Can anyone tell me what's going wrong/ what to fix? <br /><br />I've done other searches on these forums and maybe the voltage regulator/rectifier is to blame, but the voltage guage was reporting a constant 14v.<br /><br />The engine is a 1984 3.7L Mercruiser.

 

[Bt Doctur]

Re: bouncing tachometer

more likely a loose ground wire.tach feed comes from the points side of the coil.12v feed and ground supplied at the dash thru the harness.

 

[pbv]

Re: bouncing tachometer

Had the same problem on a port side tach in my 2002 searay 280 sundancerm with twin I/Os. I checked the wiring from the tach back to the engine and still had the problem. One day I fiddled with the adjustment screw on the back of the unit turning it in both directions with the engines running. I then set it to match the rpms of the starboard engine and have not had a problem since...go figure...

 

[skiMachine]

Re: bouncing tachometer

I checked the wiring from the gauge to the engine. At the gauge, the connection was tight. At the negative post on the ignition coil, the connection was loose. I tried to tighten the nut there and it just turns and turns without getting tighter. I can't losen it either and the bolt/post is not turning. <br /><br />I've never seen anything like it... any ideas?

 

[Don S]

Re: bouncing tachometer

Threads are probably cross threaded and striped. Get a new coil, and put new terminals on the wires.<br />Or, cut the wires off that terminal, put new ends on them, put a new nut on top of the old and see if it will tighten down.