Rev counter - alternator

welshspringer · Aug 3, 2017

This topic I should imagine must have been on this forum. Discovery 3o0Tdi.
I have a "small" problem, my rev counter has suddenly decided to do its own thing, switch on edition and the counter reads 1000 rpm without the engine running, when running counter reads 2000 ram at tick over. I have cleaned the contact on the back of the alternator -no change. Being not a mechanic I am stumped, a little help would be appreciated.
A side note. I was shown how to open a locked disco, my dear wife accidentally pressed the lock on the drivers door then closed it, left us on the outside looking at our phones, spare key and a dog who couldn't figure how to open the door. The recovery person had it open in Less than two minutes.

chris-the-gerbil · Aug 3, 2017

If you pull the sensor wire off the W terminal so it's not connected to anything what does the tachometer say?

welshspringer · Aug 3, 2017

chris-the-gerbil said:
If you pull the sensor wire off the W terminal so it's not connected to anything what does the tachometer say?

Hi Chris
Found the following
Key in ignition not turned on reading = 0 terminal on.
Key in ignition turned off reading = 0 terminal off.
Engine running = 1250 - 2000 terminal off.
Engine running = 1750 - 2500 terminal on. Tick over

brian47 · Aug 3, 2017

I'd be more inclined to suspect a fault in the alternator voltage regulator pack.
Check the voltage across the battery with the engine running above tick-over. To charge a lead/acid battery, the voltage should be above 13.8volts.

The other side of the 820 ohm resistor goes directly to the tacho.

sierrafery · Aug 3, 2017

The problem seems to be with the instrument in this case as it shows revs even with input disconnected.

chris-the-gerbil · Aug 3, 2017

The W terminal takes a pulse direct from one of the coil windings. If the alternator was faulty I would expect nothing to be shown at all. There will be a frequency to voltage convertor in the instrument binnacle and I expect thats where the problem actually lies. To diagnose it further though you are going to need an oscilloscope and a signal generator to make any real headway.

welshspringer · Aug 4, 2017

Thanks the help unfortunately I am just a typical driver have not got a clue what or how to use the instruments mentioned.
Big question, do I have a problem if I ignore the misreading?
I should imagine a new instrument would be expensive also to remove and replace the binnacle/instrument. I tested the battery with engine on tick over and it read 14.4volts.
Again thanks for the input.

sierrafery · Aug 4, 2017

Depending o the MY of your's you might find accessible used ones, as i dont know what year is your's here's an example for '95 e.g http://www.ebay.ie/itm/M10925-LAND-...897746?hash=item46650a8052:g:xbYAAOSw3gJZN-Ow , better than not know the real revs IMO though you should know that the stored mileage will not go down what ever you do

welshspringer · Aug 4, 2017

sierrafery said:
Depending o the MY of your's you might find accessible used ones, as i dont know what year is your's here's an example for '95 e.g http://www.ebay.ie/itm/M10925-LAND-...897746?hash=item46650a8052:g:xbYAAOSw3gJZN-Ow , better than not know the real revs IMO though you should know that the stored mileage will not go down what ever you do

welshspringer · Aug 4, 2017

Disco 300 Tdi year 1996
If that pinnacle is suitable I'll buy today.
Cheers

sierrafery · Aug 4, 2017

I dont know the differencies between D1 instrument packs but there are more versions according to part numbers which are classified according to VINs eventually check your VIN and ask the seller what vin was that....or expect someone more familiar with D1s to confirm they all work no matter of MY, here's another http://www.ebay.ie/itm/LAND-ROVER-D...-YAC-114011-/282449662281?hash=item41c34fd149

there is a similar set for vehicles VIN(last 8 characters) FROM MA500000 TO TA501919 which contains 95 and the next set from TA501920 (95/96 on)

chris-the-gerbil · Aug 4, 2017

The alternator pulley changed in size around the 1996 model years - that means that the binnacle comes in two versions as the pulse rate changes so the tachometer has to be matched to the alternator. If you swap the pulley from large to small to get better charging for example, your revs as show need reducing by 2/7th to get the right number...

welshspringer · Aug 5, 2017

Bought it, next how to take binnacle off the dash?

brian47 · Aug 5, 2017

welshspringer said:
Bought it, next how to take binnacle off the dash?

By the look of it, it's just a couple of screws and just a small amount of swearing:-

welshspringer · Aug 5, 2017

brian47 said:
By the look of it, it's just a couple of screws and just a small amount of swearing:-

View attachment 128854

View attachment 128855

Thank you Brian. Noticed you are at Bridgend, I have been marooned at Port Eynon for the past 9 weeks with numerous visits to Morriston hospital due to shattered Achillies tendon. Still a bit better than Merthyr.

brian47 · Aug 5, 2017

welshspringer said:
Thank you Brian. Noticed you are at Bridgend, I have been marooned at Port Eynon for the past 9 weeks with numerous visits to Morriston hospital due to shattered Achillies tendon. Still a bit better than Merthyr.

Sorry to hear you're sat back and got your feet up.

Yeah, Morriston is a good hospital, that's where I had a tumour in my spine dug out. I won't say anything about Merthyr, other than to say, "Yeah, I have heard the rumours".
I know where Port Eynon is, haven't been down there for years. Apparently the statue of the lifeboatman in the churchyard was related in some way to my mother's family. When that particular lifeboat, I think it was the Mumbles boat was lost with all hands, it was decided that a statue would be raised. Usually for anything like that it would be the coxswain who was recognised, but they didn't have a picture of him so they used a picture of the second cox and it was he who was related to the family.
So there you go, a bit of useless information for you.

welshspringer · Aug 7, 2017

Do not believe the rumours, there are far worse places than Merthyr. Admittedly there are some bare do wells but every village has them, from experience even places like Brecon and Usk town have them. Even some landy owners, mores the pity.

ceffyn · Aug 7, 2017

welshspringer said:
Do not believe the rumours, there are far worse places than Merthyr. Admittedly there are some bare do wells but every village has them, from experience even places like Brecon and Usk town have them. Even some landy owners, mores the pity.

have you done your binnacle yet if your stuck im only over in aberdare and went through the whole changing of binnacles thing not so long back to sort a speedo issue. be more than willing to drive over the hill to give you a hand should you need it. from memory i believe the only tool you will need is a phillips screwdriver, remove the steering column surround and then there are 2 pain in the butt screws to get out at the bottom of the clock surround. then its 4 easy screws holding the clocks in place and i think its 3 connectors for the wires on the back.

brian47 · Aug 7, 2017

welshspringer said:
Do not believe the rumours, there are far worse places than Merthyr. Admittedly there are some bare do wells but every village has them, from experience even places like Brecon and Usk town have them. Even some landy owners, mores the pity.

I know what you mean.
Gurnos, Penrhys, Trebanog. Why were all the bad reputations on the tops of big hills?

welshspringer · Aug 7, 2017

brian47 said:
I know what you mean.
Gurnos, Penrhys, Trebanog. Why were all the bad reputations on the tops of big hills?

Typical out of sight out of mind. Then build a hospital in the middle.

Rev counter - alternator

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