Audi 100 2,3E 1990 speedo problems

Hello
I have a 1990 Audi 100 2,3E with speedo problems that have been bugging me for some time. It started last summer when the speedo needle during drives from time to time stuck at about 80 km/h. It
would then after some minutes usually fall to 0 km/h where it also could stick for some minutes until is went back to indicating the speed in a normal fashion. In outbursts of aggression and brute force it has been tried to knock on the top of the padding covering the instruments with an increasing amount of voilence. Some times this actually seemed to work because the speedo needle suddenly started indicating the correct speed again, but I don't know if the hammering incidents actually have caused the speedo to start working. After some months these problems seemed to occur more frequently and a couple of months ago I got the entire panel with instruments changed to a brand new one from an Audi dealer. The cable connections also got checked and were said to be fine. Some minor components also were changed at the same time. Now the problems seemed to have reoccured with the speedo needle often sticking at 78 km/h then fast falling in a number of steps to 0 km/h and often rising again to indicate the correct speed or sticking at 0 km/h for some time before getting functional again. Right now the needle is stuck at 78 km/h and has been for a period of time. The driving speeds have been almost all over the entire range from 0 to 200 km/h when the problems have occured. Moreover the counters indicating the distance covered for the car also don't work when the speedo needle gets stuck at either 0 or 78 km/h. Any good advice on these problems?
Bjarke
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bjarke wrote:

display. If the problem was not corrected by changing the cluster you should check the wiring leading to the speed sensor which is located on the trans axle (behind the engine). I think it is on the left side (driver's side in the US).
I think that the circuit runs to the ECU and then to the IC so checking the connections to the ECU would be another place to try. Unplug the ECU and plug it in again to check for bad contacts. The ECU is located in the right side kick panel, just in front of the door. There is a possibility that the engine electronics also is controlled by a module in the left side kick panel. These have been known to get corroded connectors due to water leaking from the sun roof. They have a plastic protector to help keep them dry but moisture still gets in over time.
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Hello again
I have now checked the wiring and connections for bad contact and corrosion and I found nothing. All seems fine except the speedo is still not working properly. Right now the only thing I can think of is if this could be a fault internally in the ECU? I would prefer not to have to buy a new ECU (I just heard the price from a Audi dealer), so can I swap the ECU with the ECU of another Audi? And if so, from which models is it possible to find a usable ECU? Alternately I could also have a go at looking for a diagnosis on the actual ECU if I can find the time for it. I have access to electronic lab equipment at my university, so in this case I would like to know where to find a description on how the ECU should perform under normal circumstances?
Bjarke
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bjarke wrote:

number on it to verify. OTOH, it is unlikely that the ECU is the problem. They tend to be almost bullet proof.
Try checking this site: http://www.sjmautotechnik.com /
Or this one: http://members.aol.com/c1j1miller/main.html
AudiWorld forum for T44s would be worth a check too: http://forums.audiworld.com/v8 /
I would try to check the output of the speed sensor before doing anything else. This might require a scope but a multimeter might be enough.
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Thanks. I'll have a try at measssuring the output from the speed sensor some time when the weather looks fine here.
Bjarke
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Tony wrote:

I checked with a friend that is an independent Audi mechanic and he said that on the '91 T44 the speed signal does not go through the ECU. It is a direct connection from the speed sensor on the right side of the transmission to the instrument cluster.
His opinion is that the sender or its wiring is the problem. The part is cheap at about $30US and easy to replace.
Let us know what you find.
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If the Audi dealer changed the instrument panel for a brand new one only a couple of months ago, haven't they given you a warranty on the work?
Not sure of the consumer laws in your country but if the dealer said that replacing the panel would fix the problem and it hasn't then they haven't done their job properly and should rectify it with no charge to you.
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Oh yes, there is a general warranty on such work in Denmark. But I also remember the guy putting it someway like 'We'll have at go at solving your problem by replacing the instrument panel'. And I do understand that attitude because it seems most likely to eliminate this sort of problem by doing that - also from the advice I recieved here. And I seriously expect that the next steps in eliminating further possible causes to the problem is selling me more expensive parts.
Bjarke
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The slam on the binnacle is known as the "eyebrow dashboard salute".
This is a known problem caused by a pin soldered into the backplane that's used to support the speedo cracking the solder that holds it to the board.
The fix is a tiny touch with a soldering iron and it's documented on Scott Mockry's site at http://www.sjmautotechnik.com
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Phil Payne wrote:

problem was not resolved. Still, I suppose the both ICs could have had the same problem and symptoms.
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