Dodgy/jumpy Speedo

[ebola_one]

Hi All,

have had this problem for a wee while now, have spent a bit of time searching (here & generally the net) but have come up with nothing specific to the old Stag.

Here's what happens:

I'll be driving down the road and the speedo will jump about like mad. It does it when the road is smooth and bumpy so I'm not totally sure if it's a loose wire.

When it does settle down it's either 'close enough' (the 3-5% commonly seen) or it's wildly out - like 15% out! (I'll be doing a GPS masured 100kph and the speedo will read 115-120k!)

It's fairly similar to this, however it's never dropped right down to 0, it'll usually only jump around +/- 15km

It's just a bone stock pooh auto 1996 25x, but I'd like to try and sort the issue out. I actually think it might be having an effect on the mileage the ODO reads but I haven't confirmed this.

My avenues of fixing:

1a: Pull the dash cluster, clean the contacts for the plugs/sockets

1b: Pull the dash cluster and resolder everything (do these cars suffer from dry solder joints?)

2: find a replacement dash and see if that fixes the issue

3: plug in an OBD2 reader and see if the ECU is seeing the correct speed (I'm assuming that the speedo sensor feeds the ECU and the dash takes a feed off that wire, or the ECU feeds the dash directly)

Regarding option 3, can anyone recommend a decent cheap OBD2 reader?

Thanks for any help you can give me

[wolverine]

Have just been through this on my R33. I was assured that most of the time it due to the cluster by a number of experienced import mechanics. I changed the cluster but unfortunately it made no difference. So whilst this is worth doing if you can get your hands on one cheap it was not the reason for my jumping speedo.

The alternative is that the issue could be the speed sender on the gear box. In my case I bought a new speed sender and the issue is fixed. The small gear needs to be transplanted from the old sender and it might pay to use a new circlip which wasn't supplied. I bought my sender from the USA.

[Daleo]

If the lip seal on the drive leaks; due to the mounting position, the sender (which is just an encoder) can fill with oil.

I've seen this a couple of times on r31's, which use a similar setup.

[ebola_one]

Awesome, thanks guys I'll have a look at the VSS.

[liammph-uk]

Had a problem with mine jumping when doing under 10mph, would jump up to 60+, turned out to be a dodgy earth so it might be worth checking yours.

[ebola_one]

Had a problem with mine jumping when doing under 10mph, would jump up to 60+, turned out to be a dodgy earth so it might be worth checking yours.

Which earth? the one to the battery? or the dash earth(or some other earth under the dash)?

[liammph-uk]

The one going to the diff. God knows how it affected it but saw it was snapped and once I'd replaced it the speedo was fine.

[chef_stagea]

The more earths the better... I would be pulling the speed sender out as said. But b4 you touch anything, u need to know where its going wrong.

Ur diagnositic port will tell you what the ecu thinks, its them a matter ot going road-ecu or ecu-display..: