The tach signal comes from your alternator. No RPMs means a loose or broken belt. Erratic readings or jumpy needle could mean a loose connection or a broken wire. Some Alternator terminals are labelled for the tach. The engine manual shows which terminal goes to the tach and I've found that manual online. Suggest you check the terminals behind the tach and behind the alternator, clean, spray with WD-40 and tighten. Also check the ground on the engine
Chuck > On 07/26/2022 7:03 AM David Knecht via CnC-List <cnc-list@cnc-list.com> > 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 > > >
