Rev Counter Reading High

[stokeybloke]

I bought my MK1 Stag last August, the last owner only did about 400 miles a year so when I initially started driving it the rev counter occasionally stuck until I tapped the glass, but this hasn't happened now for several months.

A couple of days ago the rev counter sat quite happily between 2500 and 3000 rpm in 4th plus o/drive at 65 - 70 mph. Half way through the journey when I had slowed to around 60 mph I noticed that the rev counter was sitting at about 4500 rpm. The engine wasn't revving abnormally and at the next services I found that the rev counter shot up to 2000 rpm with only the ignition on (i.e. the engine wasn't running). For the rest of the journey it seemed to be reading about 2000 rpm too high. I've switched the ignition on earlier today and the needle immediately jumped to 2000 rpm.

The car has electronic ignition and the rev counter is an RVC unit.

Any suggestions as to what might be wrong ?

Thanks in advance,

[JPB]

Is the gauge fed from the module or from the coil and are both earth terminals securely attached to known good earth points on the dashboard?
Also, what make and model is the electronic ignition system? Some, such as certain Lucas Opus models, are designed to work with RVI rev counters and not RVCs.

[stokeybloke]

Hi John,

I have a standard Lumenition electronic ignition unit; the gauge has two cables connected, one goes directly to the coil and the other (dark green) goes into the original loom behind the dash, I'm not sure but it might go to the voltage stabiliser ?

With the ignition switched on and the cable from the coil disconnected the counter still sits at 2000rpm but drops to zero/rest when I disconnect the dark green cable.

Thanks for your time & help with this,

Mark