Engine off->clock runs fine, engine on->clock crawls

[aclwalker 3]

Hi all,

 

I recently posted about my MFA average speed being out but it turns out it's because the clock is playing up. I've done lots of searches for clock info but can't really find anything suitable so I thought I'd start a new thread specifically about the clocks.

 

The (digital) clock on my '94 VR6 runs fine and keeps good time when the engine is off, but as soon as I start the engine it slows down to about a third normal speed, so 30 minute trips apparently take less than 10 mins according to the MFA.

 

I took the dials out and checked for loose connections but couldn't see anything up.

 

Any ideas what could be up here? I'm thinking it's strange that the clock runs fine when the engine is off but goes very slowly when the engine is running. I'm guessing that this might mean the clock is fine but something else is up. Does this make sense?

 

I'm beginning to suspect something with the central locking and/or the various old disabled alarms in the car.

 

The reason for this is that the clock only seemed to start running at full speed again once I locked the car with the key in the driver's door (with the window rolled down and me sitting in the driver's seat). I sat and watched the clock for about 20 minutes trying various things.

 

I also started feeling around the wiring at the fusebox and got to the stage where the drivers door wouldn't lock with the central locking until I felt around at the fusebox again.

 

The central locking has never been that great. For example I can usually lock all the doors from the inside by pressing the button down but pulling it back up again won't unlock them. Occasionally (very occassionaly) I've also heard the central locking pump do a single pulse for no apparent reason while driving along.

 

Any ideas what could be causing the clock to run slowly as soon as I start the engine, but start behaving again once the engine is off and the car locked up?

 

Could there be a link between this and the central locking?

 

Could it be a problem with the voltage regulator/alternator?

 

Any help greately appreciated.

 

I would try new clocks if I had any, but I'm not that keen to try this since the clock only misbehaves once I start the engine (and so replacements might just do the same) and also I'm assuming that I'd lose my mileage reading with new clocks.

[dr_mat 0]

Take a look at the regulated Nv lines on the clocks. They'll have a step-down regulator, probably running at 5v. I would guess that the extra voltage from the alternator (I'm assuming that's all working ok) is causing problems on the dash. (Alternator is pushing 13.8 - 14.4 volts, battery alone is only 12.6v)

Obviously you also want to check the alternator output voltage and so on ..