Tacho acting weirdly

[DCatSea]

Went out for few hours today for a run into the Choptank, and all went well; even the weather gods played nicely. However, I noticed that the tachometer did not appear to be providing an accurate rpm count (based on my "ear"). It was fine for the morning, apart from sticking on startup, I revved to 1000 and it registered. Seemed to be fine up to around 1500 rpm, but wouldn't register above 2000 on a "speed run". This is on a 4D61.

I am a tacho-virgin, so any ideas on what might be the issue? Any and all suggestions are, as always, welcome.

Thanks

[TorreyWP]

If I understand the tach arrangement on a 4D61 correctly, the signal for rpm is fed by a pick up in the alternator, usually a gray wire for tach signal.

First, check to make sure the alt belt is tight, because its not registering at higher rpm, the belt could be slipping. Other than that it could be the pick up which is a component of the alternator or the gauge itself.

Hopefully its just the belt, keep us posted!

[DCatSea]

Thanks Torrey; great advice. I'll be going down for a look later in the week, and will let you know what happens.

[tego]

Doug, I have exactly the same setup as Torrey described above on my Nissan and had the same problem a couple of years ago. It was a loose belt. Be careful to not overtighten it, about 1/2" deflection is correct. Ben

[DCatSea]

Thanks Ben - I'll be going down to have a look on Thursday, once the Engine Room has cooled down to 100 degrees. The belt was renewed late last year, so it probably needs adjusting by now.