odd speedo problem

Hi, I have a weird speedo problem with my MK1 96 Punto 55S. On steep hills or when there's a big bump in the road the speedo needle will jump to 130MPH stay there for a few seconds making a whining noise and then jump back to 25MPH and stop there until another bump starts it working again normally. It did it quite a few times last night although most of the time it was working its incredibly annoying.

I got the guy I bought the car from to take a look but he could only say it was either speedo sensor or the speedo unit itself. Am taking it to a local fiat/skoda specialist next week, any suggestions on what they should look for or what it could be? I've read on here about loose earth cable possibility behind the dash but from the guides it doesn't look like there's an earth behind there that could easily move about.

I think it is likely to be a loose electrical connection or loose / faulty sensor in the gearbox because the speedo itself always goes back to working normally and it does work normally for more time than its not working. Speedo always resets to 0 when engine is stopped and sometimes resetting the trip counter had an effect.

The moment i went up the hill leaving my Mum's friend's husband's garage yesterday it did it and that led me to believe it is affected by going uphill. If it has done it then it will usually go straight back to not working after moving off after engine has been stopped but then after a while it will start working again. The connection to the gearbox has been checked.

Any thoughts? Is there a chance the speedo needs recalibrating and might be ok? Maybe i've asked too many questions. I've seen a cheap set of dials on ebay which is identical to mine - its just one hundred miles more on the clock so I don't know if its legal to replace with one of those or not after my mileage increases (but only if thats the problem)

btw i know there are a few threads about speedos but someone said to post in this forum instead of technical.

erm you are perfectly allowed to show whatever mielage you want in your car aslong as you are not changing it in such a way to increse the value of the car in a sale for example as thats fraud

you can wait till yours reaches the mles of the new one and swap them over in fact if it's only a few hundred mile difference you needent bother telling anyone or making any record and anyway who's to know

but before you buy anything its normally a good idea to find out whats actually wrong

speedos and speedo senders don't normally cause this kind of problem

what's happening is the speedo is doing a self test

they do this when they are fist powered after a long period with no power or after a power loss all my dials did this after i took them out the other day to clean a bulb and also after a dead battery

now if it is only the speedo not the rev counter and others that is doing this then it suggests a bad connection on the earth or power feed to it so you wana check the connections to the dash binicle and the circuits on the back of it see if you can see any burned or discoloured bits on the flexible circuit on the back

there are also some wires round the back of it connected to various dials with small nuts as a route thou the flat circuit was obviously impossible so like jumpers if you will that may have come lose

but with things like this 9 times out of ten it's a resistive fault in the wiring and not a fault with an actual component specially when it's bump related

thanks for the info, I was told by a fiat / skoda / alfa specialist in my area that the best bet for finding the problem was if it does it when i take it to them. I suspected an electrical fault but without more knowledge i didn't know if it was likely to be the dial/speedo unit. A friend suspected a loose cable, wouldn't mind removing the dials myself although i'm prone to breaking things and its booked in for tuesday. Now when I take it to the garage I can tell them what you've said and they won't waste time checking the sensor if its nothing to do with that. No other dials do anything weird and the clock always has the right time (no rev counter).

Sounds like a noisy speedo Cable, but lil pip has just lead me to believe it's electronic speedo? Which type is it?

Jon.

Hi, it is an electronic speedo (according to a local mechanic I know who took a look). Standard Punto MK1 so has no rev counter but I've heard they use electronic speedos.

Cool, thats my theiroy out of the window then, lol. Best of luck getting it sorted.

Jon.

Hi guys, took it to S & S Autos in Margate Kent this morning, told them what I said on here. They can't find a problem, and the speedo hasn't done it since Wednesday night IIRC. They say because the speedo is working all the time they can't do anything.

Basicly since its an old car the guy thinks I should just live with it, I don't know if it will do it more often the more I use the car but they can't do much unless its showing wrong or whatever or completely stopped... as to replacing things.

I guess I could have a go at removing the dials but maybe that's not worth it. Thanks for the help guys..

Hopefully it was a intermittant problem that has sorted itself. Gremlins in the electrics, hehe

Jon.

yeah it hasn't done it since last wednesday so touchwood it doesn't do it today.