New holland Tachometer issue

[Backhoeman1990]

Good Evening all, I have a 1999-2003 New Holland TC29D and I am having an issue with the Tachometer. The needle on idle is at 10 but as soon I raise the throttle all
The way up the needle declines to 0 however it never looses power. The fuel, hour, and temperature gauge is working properly. If anyone has any insight or had the same problem, Any help with this would be greatly appreciated!

 

[Halftrack]

The tach is driven electrically by the alternator. Check the back side of the alternator for a white spade plug and clean it and the spade. otherwise look for wire damage back to the dash.

 

[Backhoeman1990]

The tach is driven electrically by the alternator. Check the back side of the alternator for a white spade plug and clean it and the spade. otherwise look for wire damage back to the dash.

Thank you! I will try to clean it tomorrow. It only has 492hrs on it, I am thinking it was left outside possibly for a long period of time and the connections got messed up.

 

[rScotty]

Good Evening all, I have a 1999-2003 New Holland TC29D and I am having an issue with the Tachometer. The needle on idle is at 10 but as soon I raise the throttle all
The way up the needle declines to 0 however it never looses power. The fuel, hour, and temperature gauge is working properly. If anyone has any insight or had the same problem, Any help with this would be greatly appreciated!

That's odd.... about the idling at 10 rpm, I mean. Most diesels idle at around 1000 rpm.
If it goes down to zero when it is off, and only up to 10 when it is idling then I would clean the connections as a matter of course, but suspect the tachometer itself if nothing changes.

Your older tractor is probably a pre-computer type. So it would be a mechanically injected diesel with a separate line from the high pressure pump to each injector. On those, the tachometer does not have any input or influence on the way it runs.

On later computer controlled electrically injected "common rail" type of diesels using electrically controlled injectors and a fuel computer the tachometer reading is one of the inputs to the computer and very important.
rScotty

 

[TIMMYDUCK]

On my 2000 TC33D the fuel gauge and tach have been doing goofy things for a decade .

If you simply tap the shroud they straighten themselves out .

 

[Backhoeman1990]

That's odd.... about the idling at 10 rpm, I mean. Most diesels idle at around 1000 rpm.
If it goes down to zero when it is off, and only up to 10 when it is idling then I would clean the connections as a matter of course, but suspect the tachometer itself if nothing changes.

Your older tractor is probably a pre-computer type. So it would be a mechanically injected diesel with a separate line from the high pressure pump to each injector. On those, the tachometer does not have any input or influence on the way it runs.

On later computer controlled electrically injected "common rail" type of diesels using electrically controlled injectors and a fuel computer the tachometer reading is one of the inputs to the computer and very important.
rScotty

Yes it does idle at 1000, As soon as you Throttle up the needle goes straight to zero.

 

[alexpops]

Is the throttle linkage rubbing the sensor wire & grounding it out?

 

[rScotty]

On my 2000 TC33D the fuel gauge and tach have been doing goofy things for a decade .

If you simply tap the shroud they straighten themselves out .

That could mean a simple bad connection to the tach wire - which could be at either end of the wire- at the sender on the engine or where the wire connects to the gauge.

It could also be as simple as needing to run a separate grounding wire from a mounting screw in the metal of the gauge and/or the metal mounting shroud....over to a screw on the frame of the tractor.

 

[TractorTech]

It also could mean that the tach itself has a deteriorating connection on the circuit board or internally

 

[rScotty]

It also could mean that the tach itself has a deteriorating connection on the circuit board or internally

That's interesting....Sure it could. And what is interesting is if we go back another 20 years to 1979, we would find most tachs on tractors to be mechanically driven by a rotating cable within an outer cover. In essence, they were tiny generators themselves. We call them mechanical tachs, but they are actually mechanically-driven electrical generators reading in RPM instead of volts.

Being a 1999 model, puts the OP's tach more likely to be a newer type of electrical tach - one that worked by displaying RPM derived from counting electrical pulses from a magnetic sender on the engine. But that date also puts it into the transition era. In 1990 those new electric tachs were still made to mimic discrete gauges on a dash, but by 2010 they were generally showing as readouts on an screen. His could be either.

Whichever it is, if it is an electric tach then it will have either wires or a circuit board - and either one will need to have good connectors and be using the tractor frame as a ground.

rScotty

addendum: Oh, and if we go back another 20 years to 1959, we come upon completely mechanical tachometers where a rotating cable drives a little set of gears within a tachometer head gauge face that looks and works like an old wind-up pocket watch. Our old 1959 JD530 has that type.