Lost control of my rev counter!!!

[Guest]

After 2 months in hibernation due to winter/Xmas/work and backdated heating project I finally took my car ('79 SC) out for a drive yesterday. Started beautifully, first time and off we went. Except the rev counter was either waving wildly at me or having a rest against the zero stop! When I put the indictors on (or any electrical load) it waved more wildly. After about 40 minutes it stopped and all seemed ok. I assumed it was lack of use and put thecar away satisfied but confused. Then today off we went again for another great drive and the same happened again.
This time when we got back home I checked to see if I had disturbed anything during the backdating job, but nothing appeared out of place. When I went to plug in the battery conditioner I heard a funny noise which turned out to be the battery 'fizzing'. I recall reading a thread on PP last night which mentioned that a faulty voltage regulator could cause the rev counter problem and I suppose it could also cause the battery to get more charge than it needed, hence the fizzing?
Any ideas please, I'm not an expert on electrics.
Thank you
Ian

PS What a fantastic car!!!

 

[bones]

At last on the road again Ian! Incorrect current to the rev counter will cause the problem you describe, put a meter across the battery terminals and you should get about 13-14 volts with the engine running and assuming the battery is properly charged, more and it's likely to be the regulator, less and it's likely to be a failing battery , the alternator or the regulator. An auto electrician may be the way to go if you don't use a meter.

 

[Guest]

Thanks for the prompt reply Bones. The alternator was renewed 20 months ago (should be ok?), the battery is a six year old Bosch Silver and I have a spare regulator. I guess we can see an easy way of removing at least one of the culprits!!
I'll let you know what happens.
Thanks again
Ian

 

[Guest]

Must be something in the air Ian, went to take mine out for a blast the other night (after a four-month lay-up) and battery was low, not enough in it to start (have been using my conditioners on other things). Connnected my big charger and set it to boost. While that was hooked up juicing the battery, the rev counter was stuck on 3 and rising as the battery picked up volts, never seen that happen before. Once the car came to life it settled down immediately, even with lights and heater on and flat battery still being charged by car.

If it's all over the place when running then could still be battery if it's that old (would be surprised with a Bosch Silver, though it has been discharged as you say), or reg or wiring. As Bones says, if you have a meter, check what voltage it's charging at and what the battery's standing volts are. Should charge at 13.8, should be 12.75 or more static if fully charged by your alternator, anything less than 12.2v generally means it's not long for this world. Cold weather absolutely kills batteries so my money is 100% on that, but who knows.

German and Swedish are very good on Bosch battery prices by the way.

 

[Guest]

Thanks John,
I had hoped that it wasn't the battery, Bosch quality and all that. It had been plugged into my conditioner and easily started the car. Would it be warm to the touch and 'fizzing' if it was failing? I suppose that I had better change the regulator first as it is an easy job and see what happens.
Thanks again
Ian

 

[Guest]

Could be the regulator, definitely. You are right to swap that first if you have a spare mate. I have had 10 years out of Boschs so know them to be top notch batteries and wouldn't fit anything else. For some reason I originally read you rmessage as saying the battery was flat when you came to it - had a 14-month old nutter next to me trying to eat a laptop power supply at the time which might have had something to do with it.

I agree it's great to be using the car again though, whatever the problem. Pic of mine from the second night out it had last week:

 

[hetherc]

Hi Ian

Remember our trip to the OPC at Swindon? (82Y Minerva blue SC Sport Coupe). My SC was exhibiting exactly the same symptoms. Took it to Porschetech in Bristol the next week, they replaced the regulator (well actually they sent it away and someone else did it for them) and its been perfect ever since.

Might make it to Shepton Mallet on the Sunday. I'll look out for you. Pulled mine from its Carcoon last weekend too after c3 months of inactivity and had a great ride. Roll on the better weather.

Clive

 

[Guest]

Hi Clive,
Good to hear from you and thanks for the confirmation on the voltage regulator. I just fitted my spare VR after getting a reading of 17.8 volts at the battery with the engine running, no wonder the battery was fizzing!! Problem number 2 is that the car won't start now, bugger! I must learn not to rush to get a job finished at night. I must have dislodged something electrical because it is turning over but not firing. More to follow on this one.
Ian

PS I can only make it to the Bristol show on Saturday, sorry.

 

[Guest]

ORIGINAL: imcomerford

... Except the rev counter was either waving wildly at me or having a rest against the zero stop! When I put the indictors on (or any electrical load) it waved more wildly. After about 40 minutes it stopped and all seemed ok. I assumed it was lack of use and put thecar away satisfied but confused. Then today off we went again for another great drive and the same happened again.

I've been having the same sort of thing with my speedo

Haven't had the car long but it's been fluctuating between sticking at zero for a bit when you pull away, then bouncing up to approx double the true speed (scared a passenger who thought we were doing 160 down the local bypass!!). Then it reverts to normal. Currently it's OK again. No other electrical gremlins apparent.

Any theories - sender unit, speedo itself, not enough winter use??

 

[bones]

if everything was fine bfore winter came along suspect , damp , low battery charge first before taking anything to bits, take it for a good long run see how it behaves after that. The sender is an easily exchanged part but speedo repairs are expensive.

 

[Guest]

I finally got around to trying to sort out why the car wouldn't start after I had replaced the voltage regulator. I just checked all of the electrical connections around the voltage regulator, especially the one into the CDI unit and it started first time, weird!!! Anyway it is now charging at around 14.3 volts and the rev counter is firmly back under the control of my right foot. A quick hour out in the car and all is well, very happy now!!
Ian