C18NZ (Auto) - Erratic rev counter

[jgwilliamson]

Well, just over one month since my C18NZ auto passed its MOT and got back on the road

I've done almost 600 miles since then "running in" and getting to know the car again and a couple of minor issues needed addressed but it's now driving very well.

One issue that I did have was that the rev counter would intermittently read 1-1.5K revs too high while on a drive, while the engine/gearbox noise definitely didn't change at the same time. Normally I disconnect my battery when I put my old cars back in the garage (I also have a 1300 GLS Viva) and I'm now wondering if this might be the cause of this behaviour in the Cav?

For the last week or so I haven't disconnected the battery in the Cav and the rev counter now reads correctly 100% of the time whether on a short or longer run.

Could it be that the engine management needs to "recalibrate" with respect to the rev counter after a battery disconnection?

I'd appreciate your thoughts

Cheers

John

[Robsey]

I have never known a rev counter to be affected like that on a Cavalier.
I can only assume a bit of moisture in the loom, or electrical noise near to the coil or it's amplifier.

The fact that regular use appears to have resolved the issue, it can be thought likely that the issue was related to ambient damp in the engine bay, from being stood.

[jgwilliamson]

Thanks Rob,

Yes an odd one, but your explanation sounds better than mine

If it starts happening again I have got a new coil and ignition module which I can swap in.

Many thanks

John