Erratic Rev Counter

[KugaWestie]

I have the black bezel Mk1 instruments in my car.

When idling it is nice and steady.

When driving the car the rev counter jumps around a fair bit. When accelerating it will surge up the rev scale quicker than the engine for example. Then when cruising it will bounce erratically altering by approx 100rpm at times.

Any ideas what is causing this?

[mcosh]

I would guess if unlucky its the gauge but often it can be the coil lead causing it. Change the coil lead and position away from the signal wires coming off the coil.

Edited by mcosh on Monday 29th January 21:47

[Belle427]

Ignition components can cause this but a lot of cars are like it.
Ive read of people removing extenders, using different fancy leads causing it.
Worth just checking under the bonnet in the dark to see if you have any stray sparks etc or a small misfire thats hard to notice.
Is your ignition system standard components?

[pmc_3]

If you've ditched the plug extenders make sure you have changed the spark plugs for resistive ones otherwise you can get electrical interference.

[KugaWestie]

pmc_3 said:

If you've ditched the plug extenders make sure you have changed the spark plugs for resistive ones otherwise you can get electrical interference.

Yes, plug extenders are long gone and BPR6ES plugs in use

[KugaWestie]

mcosh said:

I would guess if unlucky its the gauge but often it can be the coil lead causing it. Change the coil lead and position away from the signal wires coming off the coil.

Edited by mcosh on Monday 29th January 21:47

Coil lead - do you mean the HT lead?
Signal wires coming off the coil - I assume you mean the + & - wires?

[KugaWestie]

Belle427 said:

Ignition components can cause this but a lot of cars are like it.
Ive read of people removing extenders, using different fancy leads causing it.
Worth just checking under the bonnet in the dark to see if you have any stray sparks etc or a small misfire thats hard to notice.
Is your ignition system standard components?

Thanks.

Standard apart from Resistive plugs and Craddock HT leads