Rev counter

[TVR keith]

My mate Vic's 98 Chim has a dodgy rev counter. Works OK ish, but give it a rev and the needle bounces backward and forwards. Keep the revs constant and its OK.
Any ideas?
I do wish he'd buy a PC and stop being a technophobe, then he could ask these questions himself!

[tvrbob]

I may be off the mark here but on older car electrics this was a symptom of a failing coil. As I understand it the failing coil spikes sending a spike into the rev counter which causes the needle to jump

[Cider Andy]

It's almost certainly coil related. Does a similar thing happen under hard acceleration or engine load? Has it doen this for a while? Or just started? If you fit heavier HT leads or a new 'high performance' coil this can happen. Try separating the HT leads from the coil's LT leads as much as possible. If that doesn't work the LT leads will need screening.

The other possibility, albeit much less likely is a fault within the tachometer itself.

[TVR keith]

Thanks for the replies, I will be seeing him tonight in the hostelry and pass your comments on

[jsr]

I recently fitted new coil (bosch), leads (Magnecor) and plugs (ngk) which caused the needle to go mental. It's annoying, but car still drives well. I suspect it's the leads that cause most of the problem.

[aerospoke]

Also recently got new coil, plugs and cables(magnecor) fitted but no probs regarding speedo or revcounter whatsoever! So keep looking in other directions too.

Cheers Jens

[petea]

jsr said:

I recently fitted new coil (bosch), leads (Magnecor) and plugs (ngk) which caused the needle to go mental. It's annoying, but car still drives well. I suspect it's the leads that cause most of the problem.

This happened on mine...new flame thrower coil, 10mm leads and NGK plugs - the tacho leaps alot but generaly settles.

thing is, it was at the dealers last week and he didn't think it was the any of those as his telemetry machine was fine...? He thought it may be the damper fitted to the tacho that had gone...Not so sure, i think it may be the leads and/or coil as it coincided with these being fitted.