All that or the tach itself has gone whacky. You could put a scope on the tach output wire or another tack and see. My cheap Chinese tack will occasionally decide to wander around a bit and then settle back down.
Joe Coquina From: Neil Gallagher via CnC-List <cnc-list@cnc-list.com> Sent: Tuesday, July 26, 2022 9:26 AM To: David Knecht via CnC-List <cnc-list@cnc-list.com> Cc: Neil Gallagher <njgallag...@optonline.net> Subject: [EXTERNAL] Stus-List Re: Engine tachometer 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 [cid:4073BE72-4704-4EA7-8EBA-B73B833F502B]
