930 TURBO REV COUNTER ISSUES!!

[howardstorey]

T911 930 Turbo Rev counter issues!!
Not sure anyone has any experience but my 1987 930 has just started to have some issues with the rpm clock! it seems to work fine most of the time but on occasions it seems to jump round to full RPM or when you rev to say 3000rpm it jumps round to 7000rpm and today it stopped and the needle sat flat for a while I stopped re started the engine and it worked fine!.
does anyone know exactly where the clock pulls the power from on the engine so I can check the connections etc and try to diagnose the clock itself?
H,

 

[930T]

Hi Howard, I had these same symptoms on my 930 and it was the alternator overcharging the battery (16V+). In the end the battery was cooked on my way to Silverstone! Get this checked out ASAP. Craig.

 

[howardstorey]

Craig
Thanks will take a look at that but all seems fine and never missed a beat with regard to starting and battery condition but as you say you never know, H.

 

[930T]

Mine was exactly the same, no sign of any issue with starting or charging. Keep a volt meter handy, next time the tacho starts fluctuating pull over and check the battery voltage.

 

[GazC2]

I`m with Craig rev counter issue often first sign of the Alternator on its way out

 

[vic cohen]

if ,as it sounds, its overcharging the battery will be super efficient until u get an acrid smell of burning ....in the cabin , super job cleaning the plates until it burns dry !

perhaps check the regulator ,have been known to fail

good luck

 

[Nick Paul]

I had exactly the same issue and it was the alternator diodes and voltage regulator - once rebuilt everything is fine. Be warned left untouched the massive fluctuations in charging will destroy your battery and maybe other bits as well! The alternator was checked and then rebuilt by Bristol Auto Electrics (BAE) for £150 they did a superb job -web - http://bae-bristol.co.uk

 

[howardstorey]

A big thanks to all the people who have come back on this!! looks like I will be reviewing the alternator and Battery cables in the next days,
thank you all Howard,

 

[Timspu]

Howard,
Had a similar issue recently, This time when indicators on the RPM needle would fluctuate. I also had voltage at 12.8 volts. This time I had low charging scenario. I changed the voltage regulator and now have 14 volts at the battery with engine running. All good.
Checking battery voltage with engine running will tell you its an alternator issue. If you are over charging then switching the lights on heaters etc may lower the voltage to stop the Tacho needle fluctuating.

Cheers Tim