RPM gauge needle is now swinging wildly at idle. Sound of the engine W27 doesn’t change so I don’t think the engine’s rpm’s are really changing. Needle settles right down when I boost the throttle.
This is a brand new issue. I just changed the fuel filter, but I don’t see how that would be related because the engine sounds like it’s running fine.
Any thoughts as to what’s going on?
Jim Cosgrove
FATE 30U #343
Galesville, MD
Check your alternator belt tension. It may slip some at idle but tighten under throttle?
Pat Furr
Bandolero, NS26C #133
Charlotte, VT
These are driven from the tach wire , check that it is not compromised. As well if it is an internally regulated alternator it could be a sign it has a bad diode. Belt slippage could be a cause, about 1/4 defection , belts are cheap and easy to change.
What voltage are you seeing during the RPM swings. Turn on an incandescent light and see what it does…
Loose ground wire from instrument panel ?
Safe Sailing
Cedric. Single Malt
26C # 207
Chester Nova Scotia
Thanks for all the suggestions on the tach problems. Belt seems tight and ok. (I was kind of hoping that would be the problem as that would be the easiest fix.) Still trying to trace wiring.
Jim Cosgrove
FATE 30U #343
Galesville, MD
Instead of tracing - just run any piece of wire from control panel to say an engine mount
That will confirm or not loose connection/bad wire
If that makes things works properly then run a new wire - does not do any harm to leave original wire in situ
Cedric. Single Malt
26C # 207
Safe Saling
Chester Nova Scotia
Hi Jim, is it possible that the engine is idling a tad too slow. The tach is an electronic tach and if the regulator trips out because the idle is too low the tach needle will drop to zero. If the idle speed is right on that threshold the needle will bounce. Once the engine speed picks up and the charging circuit is continually active the needle will settle down.
Hopefully it’s that simple.
Ron
Ron & Diane Schryver
“Alpha Waves” 1987 NS30U #393
Georgian Bay Midland ON
Hi Ron,
Thanks for the suggestion. I’m not sure that’s it but it’s worth looking into. The needle bounces around 900 RPM which is normal for my idle and engine sounds normal.
I’ve tried attending two short videos to show the behavior of the needle. One at idle and the other with some throttle applied.
Jim Cosgrove
FATE 30U #343
Galesville, MD
Looking at this I noticed that the volt meter is steady. Since the tach signal is generated by the alternator, one would assume it’s a tach problem, not an alternator problem. As someone mentioned, run a wire directly from the alternator to the tach and see if the problem goes away. If not, I’d say you have a tach problem. I happen to know someone who happens to have a spare tach for that panel.
Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA
Hi folks. Since I received a lot of helpful advice on this problem, I wanted to make sure I closed the loop on the issue. Turns out the problem was caused by corrosion on the connections. Once that was cleaned off, the tach is back to working normally.
As I’ve said before, our Nonsuches are awesome but it’s this owners group that makes them truly outstanding. Many, many thanks for your help.
Jim Cosgrove
FATE 30U #343
Galesville, MD
Thanks for following up!