DII Tachomater not a zero

[jrolfedrev]

I have a DII 2000 replaced with 2002 engine last year, everything is running fine well I have a dreaded 3 amigos but the tachometer does not default at zero. Even at speed of 20 mph the tach runs at 2000 RPM now on freeway at 70-75 mph the tach goes all the way to 4000 rpm. My two other rover 1994 DI and 2000 Range when running at 60 -70 mph tach showing at 2000 rpm, can someone give me advise as to what's going on?

 

[mbrummal]

are you in 4th gear (drive)?

 

[jrolfedrev]

are you in 4th gear (drive)?

yes.

 

[apg]

The tach takes its 'sense' from the alternator and divides by three to get the engine RPMs. When the tach starts doing something funny, the alternator is the first place to look.

Cheers

 

[mbrummal]

The tach takes its 'sense' from the alternator and divides by three to get the engine RPMs. When the tach starts doing something funny, the alternator is the first place to look.

Cheers

Not on a D2. It gets its signal from the ECU. It is either a problem with the tach itself, the signal it is getting from the ECU or messed up wiring.

 

[KyleT]

Not on a D2. It gets its signal from the ECU. It is either a problem with the tach itself, the signal it is getting from the ECU or messed up wiring.

check the ground nuts on the right side of the engine bay, i had one of mine loose and it caused the tach and speedo to do wierd things. eventually lead to it dying at random times...

 

[jims95]

If the tachometer signal is from the back of the alternator, you probably have a different pulley size on the 2002 engine, than the pulley size on the original 2000 engine.

I once purchased a higher output alternator for a Discovery, and put it on my 1995 Range Rover Classic (Serpentine belt pulley). My tachometer immediately read at higher RPM. I went back to the auto parts store to get the original pulley changed, and the tachometer was reading normal again.

The higher output alternator pulley was a smaller diameter, than the original pulley.

 

[mbrummal]

Directly from the rave manual:

The tachometer is an integral part of the instrument pack. Located next to the speedometer. it displays engine speed in revolutions per minute. It is an analogue gauge with a maximum reading of 6000 rev/min.
V8 and diesel variants use the same gauge.

The input for the tachometer is from the ECM. It is a digital signal at 2 pulses per engine revolution. When the ignition is switched on with the engine not running, the ECM will generates pulses equivalent to 228 rev/min for diagnostic purposes. The tachometer will not register a reading, as it only indicate engine speeds above 228 rev/min.

The alternator has no direct relationship to the tachometer on D2s. That is only for D1s and RRCs.