Jumping Speedo

Am having the weirdest problem with an 02 Ford Focus 1.6L Zetec - at random times and random speeds the speedo starts jumping up and down for a couple of seconds to a couple of minutes and in fact does not
stop until the car's engine has been switched off or is idling,
Has anyone out there experienced a similar problem with a Ford or have any idea what may be causing it. Investigations by my local garage confirm that this is not an electrical issue.
Cheers
Cat
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@hotmail.com wrote:

The speed signal is electrically generated from the VSS (Vehicle Speed Sensor) mounted on the transmission. This is fed to the ECU. The ECU sends an electrical signal to the speedometer.
I would be interested to know by what logic your local garage arrived at the conclusion that it is not electrical...
Does the car run fault-free otherwise? If it has a mis-fire, suspect a coil pack fault causing interference.
When the speedo is playing up does the milometer show "----"? If so, check the wiring to the VSS, especially the connector on the top of it. If you have to change the VSS just to eliminate it, the cost is about 25UKP and a bit of a fiddly job to do yourself, or about 100UKP for a dealer to do. (Google in this group for VSS - you will find plenty of info!)
Post back and let us know how you get on.
Chris
--
Remove prejudice to reply.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.