rev counter needle bounces

[kiwi 911]

Under hard acceleration my rev counter needle wildly bounces. Being a Carrera 3.0 with 6800 redline, it's not easy to replace.

What causes this and can this bouncing be fixed?

[Gwyn911]

This could be an indicator that your alternator is on its way out.

[wildcat077]

My RPM needle bounces as well,it has been doing it for three years,ever since i got my car.
A lot of people will send their tachometers to North Hollywood Speedo for calibration/modification and damping...
Just haven't gotten down to it yet !

Cheers!
Phil

[silver911rdb]

Usually an indication that your voltage regulator is not working properly. Do a search and you'll find more info on it. My car did the same thing. I replaced it and now the tach works fine.

[Targalid]

Try cleaning all connections related to the voltage regulator and tachometer. Humidity and time combine to make electrical problems.

[wwest]

Voltage regulator has, is failing. Regulator "calling" for more alternator output than is needed but alternator cannot supply that level except at HIGH engine RPM. Rev the engine up, the alternator output goes over-voltage, >16 volts, the CDI SCR begins to self-trigger sending extra pulses to the tach.

May be as simple as poor electrical connections front to back, battery ALL the way up front vs alternator in rear. But more likely regulator or alternator.

[andyt11]

Mine did the same after putting the engine back in. If I remember rightly the earth strap on the gearbox and the earth strap on the left side of the intake manifold were found to be loose. One of them when tightened, made the bouncy tach go away.

Could be voltage reg though too. Worth a check of your connections though before ripping into anything....