512BBi Speedometer trouble

had the same problem once. but as sudden as it cam it went away again. and since then no problem anymore. don´t ask me why

 

I have had the same pb for the last eight years and couldn't get it fixed despite trying to get it fixed and having various shops looking at my car... I have the pb with speedo mainly but also rev counter. I think the fault is heat related since it works fine when I start.
Possible culprits are faulty dinoplex or electrical fault (bad grounding.)
It's driving me nuts and spoiling the driving fun for me.
Good luck in finding the cause

 

may I see it right?
the speedometer shows the speed your are going and also counts the mileage - the RPM meter shows as it says the engine rpms
sorry, get sometimes confused with the english words

 

Yes, you've basically got that right, but to be more exact in English:

The speedometer measures the speed that you are going, and the odometer measures the mileage traveled -- both of these use the same signal coming from a sensor somewhere in the gearbox/diff system

The tachometer measures the engine RPM using a signal coming from somewhere in the ignition system.

A problem that only occurs in the speedometer/odometer OR the tachometer is usually related to the sensor for that system or that particular gauge.

A problem that affects both the speedometer/odometer AND the tachometer at the same time would most likely be related to the (common) +12V power and ground used by both systems.

 

thank you steve for explaining speedometer, odometer and tachometer
as english is not my motherlanguage I got often confused, now all clear ! ! !

 

Hi Peter, salut Julien,

I put my bets down to bad ground somewhere in the cricuit.

The current flowing is very small, but may result in increased resistance at the ground when flowing for some time. Temperature and humidity may strongly influence the resistance on a poor ground as well. Failure of electronic components such as capacitors becomes permanent after some time. That's why I bet on poor ground.

Cleaning ground connections is a fun weekend project ... ask me how I know ...

 

Peter, did you put a small drop of fine oil on its turning point of the speedo needle ? Cars that ar'nt run during winter often have this problem. The oil of turning point gets hard and greasy.

 

Doesn't the 512BB have a typical Veglia speed sensor with internal electronics? All electronics don't like extremes of heat and will eventually fail.

Here's a tutorial on diagnosing/repairing Veglia sensors

http://www.dinoplex.org/instruments/vegliaspeedosensor/

 

How about a new speed sensor? It's easy to get to and not too costly. In fact I think the 308 uses the same sensor?

 

That's a good point. Fitting new internal components doesn't sound too difficult, but you could damage the case on the sender when you're trying to get into it. The metal case is crimped.

 

I forgot to say, my speedo (not swim suit) died so I replaced the sender and Bingo..fixed. Quick, easy, cheap.

 

Ask Adrian?? He's a god with these Ferrari electrics. Eats this stuff for breakfast! Something to do with a the regulator in the board perhaps???