Disco revcounter

[ilovedmymantas]

After a long period of silence my revcounter has decided to act up again

I parked up today, switched the engine off and back to ignition on to keep the radio working.
For some reason the revcounter was having a little dance

https://vimeo.com/387327676

Nothing but the radio was on.
In the past it would do it with everything switched off , a distant soft clicking (solenoid?) behind the dash and the eml pulsing.
That cleared itself ages ago and the car seems to be running well now. This time it's just that one dial, no sound or light

[Robsey]

That is odd indeed.
Looks like a stray voltage signal.
It only takes a few millivolts to deflect a needle on a gauge.
I was a little worried to see it flick over to full deflection at one stage.
Many more of those could damage the gauge.

I suspect a stray voltage or a poor earth.
Only things that would flick over like that would be check control, Air Bag or ABS modules or the ECU checking for an RPM signal.
Check control is less likely, but it is one of the things on a car that goes through a check cycle when you power up the ignition without starting the car. Hence why I mention Air Bag and ABS signals.

Obvious comment is to look for a dirty earth to the ECU, Rev counter,
or look at the coil low tension green rpm signal wire.

Hopefully nothing more than a little ambient moisture due to the cold weather and condensation.

[James McGrath]

I had a similar problem on my LS about 10 years ago. Not quite as extreme but the dial would go up and down as you were driving along. It basically meant that the rev-counter was unusable.

It did it for a good couple of years I think.
One day it just stopped and it's been fine ever since.

[ilovedmymantas]

Seems to have sorted itself

[James McGrath]

Jolly good!

Mine stopped acting up when the car got very damp while it was being stored under a slightly leaky car cover.
It's now kept in a dry garage and the rev counter is still fine so I'm not sure what happened there.
Cavaliers have a mind of their own.