Thanks Neil- I will check the connections and report back later in the week. Dave
David Knecht Rear Commodore Thames Yacht Club New London, CT > On Jul 26, 2022, at 9:25 AM, Neil Gallagher via CnC-List > <[email protected]> wrote: > > On small diesels the tach gets its information from the alternator, it uses > the frequency of the alternating current, proportional to the alternator's > RPM, before the current goes through the rectifiers to be converted to DC. > This could mean the electrical connection on the alternator for tach (usually > terminal marked "W") could be loose, or a bad connection between the > alternator and the tach. If the speed showed slower it could mean the belt > is slipping but in your case it's showing higher, so more likely in the > connections or in the tach itself. > > Neil Gallagher > Weatherly 35-1 > Glen Cove, NY > > On 7/26/2022 7:03 AM, David Knecht via CnC-List wrote: >> Yesterday, I was motoring and noticed that the engine tachometer was acting >> strangely. It would read 4000 rpm for a while and then drop back to 2000 >> rpm (roughly correct). Then it would go up to 3000 rpm and hold there. It >> kept bouncing around while the actual engine was steady, so it was just the >> tach. I have no idea where the data comes from, what would cause this, and >> whether to worry about it. The engine is a Universal M4-30. Thanks- Dave >> >> S/V Aries >> 1990 C&C 34+ >> New London, CT >> >> >> >
