E30 Zone

My speedometer amd MPG meter have a new life of their own .
When driving the speedo jumps intermitantly , if i pull the clutch it carries on jumping around up to the speed i'm going and down to zereo then up and so on plus the MPG Meter goes to zero when accelerating , rev counter , fuel gauge , temp gauge are fine , any ideas anyone please.

All (probably) down to an internal break in your wiring to the speed sensor in the diff., very close to the diff.

is there any tests i could do to make sure its not the cluster

if i can't see any breaks or damage to the cables what next , can i get to the sensor? thanks

thanks willnz.

teatime39 wrote:My speedometer amd MPG meter have a new life of their own .
When driving the speedo jumps intermitantly , if i pull the clutch it carries on jumping around up to the speed i'm going and down to zereo then up and so on plus the MPG Meter goes to zero when accelerating , rev counter , fuel gauge , temp gauge are fine , any ideas anyone please.

Sorry to jump in on the thread but my motor has a similar problem but its the fuel gauge and mpg meter that keep jumping irratically at least i now have an idea what to look for

Alright mate.. I had the exact same problem.. Just changed the speedometer with a known good one and it was all fine.. It looks like the MPG needle works off the speedometer.. Id advise to change it with a good working one and if the problem carries on then you know its the wiring from the cluster to the diff

Ajsingh wrote:Alright mate.. I had the exact same problem.. Just changed the speedometer with a known good one and it was all fine..

More than nine times out of ten, this problem will be caused by the wiring near the diff. sensor, and since the wiring is easy to check, and it's free to do so, this is the place to start.
Of course the MPG econometer works from the speedo. How can it work out MPG without information on the distance the car is travelling? The other input to the meter is the fuel injector pulse width from the engine ECU.
Slight jumping of the fuel gauge is usually down to a small brass nut on the back of the instrument cluster being loose, and larger jumps, especially occurring when there is a certain quantity of fuel in the tank is generally down to a faulty or damaged level sender in the tank.
If you have a faulty speedo and a jumping fuel gauge, and both symptoms occurred at the same time, I would check out the plug and socket under the right hand side of the rear seat base, as both signals pass through this connector.

Brianmoooore wrote:

Ajsingh wrote:Alright mate.. I had the exact same problem.. Just changed the speedometer with a known good one and it was all fine..

More than nine times out of ten, this problem will be caused by the wiring near the diff. sensor, and since the wiring is easy to check, and it's free to do so, this is the place to start.
Of course the MPG econometer works from the speedo. How can it work out MPG without information on the distance the car is travelling? The other input to the meter is the fuel injector pulse width from the engine ECU.
Slight jumping of the fuel gauge is usually down to a small brass nut on the back of the instrument cluster being loose, and larger jumps, especially occurring when there is a certain quantity of fuel in the tank is generally down to a faulty or damaged level sender in the tank.
If you have a faulty speedo and a jumping fuel gauge, and both symptoms occurred at the same time, I would check out the plug and socket under the right hand side of the rear seat base, as both signals pass through this connector.

Brianmoooore that is a great help in my case i have also noticed the service light indicator green lights also flash at the same time fom one green to all the greens so i assume this is also related to what you say thanks for the info

willnz wrote:If your service indicator lights play up, it is generally a fault with the SI batteries.

SI batteries it jump when the rest of the guages jump thats why i assume its related to the above but what do i know i am a novice on these cars

willnz wrote:If your service indicator lights play up, it is generally a fault with the SI batteries.

Willnz i just did a search for S1 batteries and all is clear now thanks mate

Duff SI board batteries make the service lights, rev counter and temp gauge do all sorts of odd things, but do not normally affect the fuel gauge or speedo.
I suspect that this could be a 'one off' fault - possibly a problem with one of the power feeds to the cluster.
Start by removing the cluster, but not unplugging it. Wriggle the white and blue plugs with the engine running and see if it has any effect. A cracked solder joint or two where these sockets solder to the PCB is a distinct possibility.

Thanks everyone for your help , it was the cable by the diff to the sensor , it must have happened in the past as it is joined by a connector block , i removed the connector block and crimped the cables , all working fine , thank you again .

Copper is a strange metal. If subjected to vibration above a certain strength it will change from a soft, ductile metal into a much harder, brittle metal. This is what happens to the wires near the diff, and the ONLY practical cure is to replace at least the last 200mm of wire to the diff, complete with plug. Anything else will result in a temporary repair at best.