Erratic Rev Counter

[pw8757]

Can anyone please give me some advice about a slight problem my 1998 Disco has, even though it is more aesthetic than anything?

The rev counter needle sometimes starts to flap up and down, giving a reading of between 1k and 1.8k revs, although the engine (V8 3.9 efi running on LPG) doesn't miss a beat?

The problem particularly manifests itself when trundling along the motorway with the cruise control set to about 55mph (speedo reading). It doesn't seem to have any relationship with the load the engine is under, e.g. slight incline or downslope.

I know what the various bits of the ignition system are meant to do, but am reluctant to fiddle without some guidance, just for the sake of a needle wavering, but it can get distracting at times!

[daveyboy300tdi]

There's an electrical connection on the back of the alternator, it's where the revs are read. Give it a nip with some pliers, sound's like it could've come loose.

[teabag]

The rev counter picks up it's info from alternator pulses, there is a wire (white) at the back of the alternator and that may have an iffy connection.

[pinny]

mine started to do this although its a diesel and it was the alternator it lasted for about a week until it died new alternator and it was all ok chris

[pw8757]

I put in a new alternator about 12 months ago - no problems with the battery charging - so I'll have a look at the connections.......

Thanks guys.

[filthy]

As TEABAG says, the rev counter is fed from the alternator.

The tag that makes the connection can corrode, as does the spade terminal that plugs over it.

A good wiggle & squeeze up the spade terminal a little should solve it, unless the alternator is fried.