Rev Counter Going Haywire!

[markv]

Driving in this morning, the rev counter started acting up (the car itself was fine, just the rev counter readout). At random, the needle fluctuates erratically, at times going beyond the maximum on the scale or going below zero and hitting the limiter. The radio crackles each time the needle does something funny. Alternator readout shows normal charging. I assume some sort of electrical issue, but where do I start? I last drove her last week, and there were no problems at all then.

Given the car's performance is unchanged, I assume I'm not doing any damage continuing to drive?

[roy666]

mark - happens to mine as well. which is a 96 S2; sometimes it goes crazy with no change to the engine... and then calms down. hasn't done it for a while now. Don't have a clue whats causing it, but don't think there is any harm

Mike

[maz_r]

The signal feed for the rev counter comes from the baseplate of the coil pack, passes through a couple of harness connectors up into the binnacle and then to the instrument pack.

Assuming that all of the other instruments are working ok, it's unlikely to be the supply as all the instruments use the same power feeds.

Personally, I'd start by giving the baseplate the once-over, paying particular attention to (according to the Wiki) the connection of the brown wire which is the rev counter/tachometer feed. If that doesn't help, move on to reseating the harness connectors in the binnacle and the one down by the ECU.

The good news is that, given the engine seems to be running fine, you aren't doing any damage to anything else excepting that crackles on the radio implies electrical sparking, and that is never a good thing....

Hope that helps.

[peteoddcar]

I have been thinking about this - given the other symptom of radio crackle at the same time it could be linked to the coil pack as suggested, theres a braided ground strap from the coil pack to the longeron, ( at least on the S1 cars - I know - I designed the ground straps!) also a harness ground eylet which is in that area - make sure this is there, clean and tightened.The inline connector check is also worth doing.
Also check the mutiplugs on the back of the cluster - a wiggle test with the engine running might reveal the fault.
Let us know what you find - especially if others are having similar issues.
Pete

[markv]

Thanks - I'll try the above suggestions when I get some time...... in the meantime, when I came to drive home the problem had gone away! Just like with my PC, it seems that turning it off and then back on has done the trick!

[markv]

I spoke too soon - the problem returned today

I noticed that it happened more often while travelling over poor road surfaces and wondered whether it might be one of the battery leads. When I opened up the battery cover I discovered the possible cause: some wires from a trickle feed charger connector have come off the battery terminal, and I believe these may have been causing intermittent shorts if the wire was earthed while flapping around, e.g., going over bumps. I've removed the wires and will see what happens next time I go for a drive.

[peteoddcar]

Did you get this solved?
I now have my car out of storage so I have a reference vehicle - the ground strap on my car is not braided it is just a 1.5 ish dia( 4mmsq) black wire.
- shows that my memory is fading!