ECU fault

lefthooker · 21-04-13, 07:57 AM

I replaced the ecu on my 1981 ur quattro a while ago due to a fault, where it would run fine from cold for several minutes and then cut out. It would restart fine and run for a few minutes,then do the same again.
You could restart the car every time but the length of time it ran got shorter and shorter presumably as something in the ecu got warm.

I've still got the old one and now want to fit it to another ur but it obviously needs fixing.

Anyone got any idea if it's an easy fix or should I get somebody to repair it?

msh · 21-04-13, 09:16 AM

Easy fix, as long as you as you're used to soldering iron, have electronic device soldering experience and spare parts at hand

If I would have such a need, as a person with limited electronic knowledge [despite having acceptable soldering skills and ability to understand schematics] I would run the ECU with case removed to see what heats up and then bring it to electronics repair shop, unfortunately I doubt there's such specialists in UK by now, as britons have gotten used to discarding working stuff long time ago, not even talking about damaged, leaving only expensive specialists, which may reject your ancient ECU... Let's hope I'm wrong

4v6 · 21-04-13, 09:32 AM

Google. "ecu repair specialists uk" brings up a good list.

Looking for things heating up in the ecu isnt probably going to work as youll tend to find that only happens if a component failure leads to higher current being passed to a component thats not able to deal with it, so heat, smoke and fires!
What youll find for example is, say an injector has apparently failed to fire when it should.
initially most folks would think the injectors gone bad and that does happen, but if the injectors ok and functional then you can check for a signal to the driver ( its basically a power transistor bolted to the case to sink the heat out of it) and see if the actual driver is getting the signal to fire the injector.
If the drivers gone down (also happens) then although youll have a signal to the driver of a small magnitude( cos the transistor amplifies the signal to run the injector) therell be no output signal to run the injector which you could teset for with a simple noid light.

Thats just an example of what usually goes on rather than any particular pointer to your problem, id hazard a guess at yours that a dry joint on the board is warming imperceptibly and making/breaking contact or raising the resistance of the joint causing that cutting out issue,that can be caused by water ingress etc or just a bad joint made when the ecu was first manufactured.

lefthooker · 21-04-13, 11:54 AM

Would be nice to think it's only a dry joint.

Thanks very much for the help and advice guys

Cuppatea · 21-04-13, 09:10 PM

Not used them for ecu repairs or diagnostics myself, im not connected to them in any way, but when i phoned for help with a poorly renault they seemed very helpful and to the point.

http://www.bluehawkelectronics.co.uk/

lefthooker · 21-04-13, 09:25 PM

Quote:

Originally Posted by Cuppatea

Not used them for ecu repairs or diagnostics myself, im not connected to them in any way, but when i phoned for help with a poorly renault they seemed very helpful and to the point.

http://www.bluehawkelectronics.co.uk/

Thanks for that, might give them a call if I can't sort it

21-04-13, 09:16 AM	#2
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	Easy fix, as long as you as you're used to soldering iron, have electronic device soldering experience and spare parts at hand If I would have such a need, as a person with limited electronic knowledge [despite having acceptable soldering skills and ability to understand schematics] I would run the ECU with case removed to see what heats up and then bring it to electronics repair shop, unfortunately I doubt there's such specialists in UK by now, as britons have gotten used to discarding working stuff long time ago, not even talking about damaged, leaving only expensive specialists, which may reject your ancient ECU... Let's hope I'm wrong

21-04-13, 09:32 AM	#3
4v6 Ex Member Classic Audi Club Member Join Date: Dec 2007 Posts: 5,565	Google. "ecu repair specialists uk" brings up a good list. Looking for things heating up in the ecu isnt probably going to work as youll tend to find that only happens if a component failure leads to higher current being passed to a component thats not able to deal with it, so heat, smoke and fires! What youll find for example is, say an injector has apparently failed to fire when it should. initially most folks would think the injectors gone bad and that does happen, but if the injectors ok and functional then you can check for a signal to the driver ( its basically a power transistor bolted to the case to sink the heat out of it) and see if the actual driver is getting the signal to fire the injector. If the drivers gone down (also happens) then although youll have a signal to the driver of a small magnitude( cos the transistor amplifies the signal to run the injector) therell be no output signal to run the injector which you could teset for with a simple noid light. Thats just an example of what usually goes on rather than any particular pointer to your problem, id hazard a guess at yours that a dry joint on the board is warming imperceptibly and making/breaking contact or raising the resistance of the joint causing that cutting out issue,that can be caused by water ingress etc or just a bad joint made when the ecu was first manufactured.

21-04-13, 11:54 AM	#4
lefthooker Senior Member Classic Audi Club Member Join Date: Feb 2011 Posts: 2,655	Would be nice to think it's only a dry joint. Thanks very much for the help and advice guys

21-04-13, 09:10 PM	#5
Cuppatea Grown up member Join Date: Feb 2011 Location: Somerset Posts: 105	Not used them for ecu repairs or diagnostics myself, im not connected to them in any way, but when i phoned for help with a poorly renault they seemed very helpful and to the point. http://www.bluehawkelectronics.co.uk/