Speedo Problems.

[phoenix70]

Hi Guys,
I’ve got an issue with my speedo, and I have tried many things to resolve it, but nothing has solved my problem. 1994 MR2 Turbo Mk2 Rev 3. If the car has been sitting for a few hours (i.e. overnight or when I take it to work, 8 hours) the speedo works, although it does over-read pretty badly (Actual 70mph – reading 85mph) and at low speed it under-reads slightly (Actual 30mph – reading 25mph). After driving for a while, the speedo needle begins to fluctuate a little and funnily enough the over-reading gets less. A while longer and the speedo will stop working then jump back into life a few seconds later, normally this happens a couple of time until it stops working all together and the engine management light comes on. From my observations it seems to worse in stop-start traffic, one day it work for 20 or so miles, but the main thing I thought of, was I hadn’t had to stop at all, but on the way back from work that day in the stop start traffic, it failed after only 5 miles. My big fear is that the cog on the diff is damaged and I’ll have to pull the gearbox to fix it.
So what have I tried already, I’ve replaced the speedo sender and speedo itself; I’ve re-wired the speedo sender and run a new signal cable to the speedo itself, none of which has made a bit of difference.
Any advice will be gratefully received, this is annoying me so much, I've considered just selling up.
Cheers for reading

Scott

[bobhatton]

What were the teeth like on the sender you took out?
Have you had a look into the box with the sender removed to see what the gear teeth are like?

[phoenix70]

The teeth on the sender where fine, no sign of damage at all. I've used a endoscope camera to look into the box and the gear on the diff looks ok.

[MR2Pagey]

The gear on the diff is plastic, and I've never seen one knackered or worn. You say you've re-wired, did you make up a new wire and run it from the sender to the clocks, or to the ECU?

[phoenix70]

I rewired from the sender to the speedo

[mrfil13]

I'm sure the connection from the sender goes to the speedo the to the ecu from there.

I just replaced 2 capacitors on the back of my speedo, one you could see it leaking onto the board.

My speedo was always slightly out then one day it was miles out.

Replaced the capacitors, it's now spot on against the GPS.

[MR2Pagey]

Hmmm, does that definitely go from the speed sensor straight to the clocks and not the ECU first? So have you changed the whole clocks unit or just parts of it?

[phoenix70]

From what I understand, the speedo sender goes to the speedo, then from the speedo back to the ECU. I changed the entire cluster.