haunted speedo -latest

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Derek - 22 Jul 2008 23:49 GMT

Just to remind folk Miles the 300Tdi Disco has the electronic speedo which
is driving me nuts as it suddenly jumps into high speeds while the car is
standing still.
Replaced the speed transducer which didn't make much difference
.Recieved another instrument binnacle thru the post today, fitted still
doing it.
Another suggestion is the alternator might be producing the problem which I
first noticed when the water pump started irrigating the engine bay so it
may have contaminated the regulator pack, the tacho is however not giving
problems. I gave the alternator a good squirt with degreaser then cleaned it
with switch cleaner spray before drying off with the airline blow gun and it
seems worse so I could be on the right track.Hopefully tomorrow morning when
any cleaner that didn't get blown away will have evaporated so it might
improve?
It seems I am not alone have a look at this which is displaying the same
symptoms

http://uk.youtube.com/watch?v=3LMgWiSQaQk

you may have to turn up the brightness a tad.
Derek

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Austin Shackles - 23 Jul 2008 08:16 GMT

>Just to remind folk Miles the 300Tdi Disco has the electronic speedo which
>is driving me nuts as it suddenly jumps into high speeds while the car is
>standing still.

The tacho does that if the power supply is iffy. Had that on the bus, was
an iffy fuse in the end.

Unfortunately, the ABS fault is not. It'll mostly accept a new fuse without
eating it but any significant physical shock in the vehicle makes it blow.
Taken the fuse up to 30A (meant to be 5) and it's still doing it, so it must
be an intermittent short somewhere. Now I've got to try to find which bit
of loom it runs through.

Could be in the ABS ECU, of course, but unlikely. Unless the innards of
same have come loose.

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Derek - 23 Jul 2008 20:57 GMT

>>Just to remind folk Miles the 300Tdi Disco has the electronic speedo which
>>is driving me nuts as it suddenly jumps into high speeds while the car is
[quoted text clipped - 13 lines]
> Could be in the ABS ECU, of course, but unlikely. Unless the innards of
> same have come loose.

Thanks Austin discount the ABS cos' it ain't got one. My thought is the
power supply is different to the tacho coming from alternator pulses but
the speedo relies on pulses from the transducer so if the supplied DC power
to the transducer is 'dirty' with spikes caused by maybe a capacitor or
diode breaking down it may give erratic readings - any sparks out there
want to venture as to whether I am on the right path?

Derek

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Austin Shackles - 24 Jul 2008 08:06 GMT

>>>Just to remind folk Miles the 300Tdi Disco has the electronic speedo which
>>>is driving me nuts as it suddenly jumps into high speeds while the car is
[quoted text clipped - 20 lines]
>diode breaking down it may give erratic readings - any sparks out there
>want to venture as to whether I am on the right path?

ah, sorry, were divided by a common language here. I was talking about the
tachograph on the minibus, not a tachometer in the LR, which is indeed as
you say driven from the alternator.

I'd still go with a wiring issue creating erratic/spurious signals though. I
know on the tachograph, a brief power spike in the supply can make it track
all the way up to the top and then back.

solved my ABS fault - the semi-trained simian assembly workers at LDV hadn't
secured the wiring loom correctly under the dash, allowing it to hit the
pedalbox and eventually wear through the insulation on the live ignition
supply to the ABS ECU, causing intermittent short when going over bumps etc.

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