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Rev counter all over the place

Does anyone know the best place to look for faults on a rev counter?

300 tdi Disco (1997) and speedo works ok. However, I noticed tonight that the rev counter is jumping all over the place. At first it was fluctuating between 1000 - 2000 revs, but then when I slowed down for traffic lights it went right down to 0.

Accelerate off and it generally hovered between 1000 and 1500, but was very erratic and 'jumpy'.

Is this likely to be a dodgy wire or sensor somewhere, and if so, where abouts. I've been pouring through the Haynes manual and can't really see anything about the tacho, other than removing the dash board gauges, and I'm pretty sure that's ok and it's probably a sensor or cable somewhere?

Does anyone have any ideas?

Paul

Reply to
Paul Vigay
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If it's the same as a 200Tdi which I think it will be then the rev counter picks up a speed reference from an AC pulse from one of the phases on the alternator (may be a thin white wire IIRC) so it could be a loose connection, slack or slipping alternator drive belt or loose pulley or maybe the alternator is on it's way out (worn brushes and losing the field connections) etc.

Martin

Reply to
Oily

As Olly says, look at the connectors to the alternator. They might look OK, but it's a good thing to replace them anyway, worked on my Disco a treat. Old ones looked good, but were corroded underneath so not making proper contact. (Too much wading and mud, I think) ... ;)

Reply to
Paul - xxx

Aha! Excellent. Thanks for the help.

It looks like it was indeed the thin white wire, as I've cleaned it all up and refitted it and a quick drive round the block seemed to be a much more stable rev count on the dash.

I'll find out for sure next time I go for a long run. :-)

Mind you, if it does break, there's not an awful lot of play in the wire so I don't think there's enough length to cut a bit off and refit the connector - and I don't fancy re-wiring the entire wire!

Thanks again! Paul

Reply to
Paul Vigay

cut and properly join in (solder and heatshrink) an extension, or a bit of extra length with a new connector at the end.

Reply to
Tom Woods

On or around Wed, 12 Sep 2007 06:36:24 +0100, Paul - xxx enlightened us thusly:

wot they said, and also check alternator mounting/earthing and it can be an early-warning sign of an alternator on the way out.

Reply to
Austin Shackles

Alternator output runs the rev counter. If your alternator is dodgy then the rev counter will now register. I guess the if its reading all over, then its probably corroded connectors on the alternator. Bryan.

Reply to
b.baskerville

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