Quote:
Originally Posted by peterux
Hi Nigel,
very pleased to hear that you have solved your idle problem. 
Like you, I have no idea what would cause this problem but I'm wondering if the ECU has other switched earths?
As you have hard wire grounded one of them, maybe you have also grounded other switched earths by the internal connections inside the the ECU.
It's also worth thinking about why this switched earth was not switching? I guess it could be a fault in the ECU but i'm wondering if there an input to the ECU that it needs to see before it switches the earth. I don't have an e36 Bentley manual but IIRC in the e46 manual there is a table that describes all the ECU inputs and outputs?
But maybe if it works OK, why worry  |
Thanks Peter.
And the very same thoughts are bouncing around my head. (And the more I try to understand what is going on in the ECU, the more I realise just how much room there is in there for those thoughts to bounce around in.............!!)
Looking at the diagrams I am fairly comfortable that the swithed earth that I have hardwired is dedicated to the O2 sensor (as was the case to my hardwiring solution to my fuel pump problem). But what I do not understand is what swithes the earth on. In the case of the fuel pumps I can look at the diagrams and convince myself that the swithed earth is provided by the immobilisatiion system (and that makes a lot of sense) but I am not so sure for the O2 sensor. The Bentley Manual says that you need to measure the voltage (I was missing) with the engine running, not just with the ignition swithed on, so probably the switching for the O2 sensor earth occurs once the ECU detects the engine running (ignition, cam position sensor, crank position sensor etc.) Given that all those must be working for the engine to run, I too suspect a minor ECU fault.
But at the moment I am firmly ignoring that, leaving it to one side and getting on with building!!