HI all,
I have a weird what i presume is an earthing problem.
Some history -
Basically the SPI was running rich and with diagnostics it was found the Lambda sensor circuit was faulty.
Lambda sensor was changed with bosch original and the ECU was also sent away for overhaul/fix by ATC.
Everything came back but was not fully tested until today (lots of other work to do also). The car started ok and seemed to run with no problems yesterday and today was reinstalling the bonnet when there appeared to be an electrical connection between the bonnet stay and the ECU.
On checking with ignition off there was indeed +12 Volts on the ECU cover. (measured volts between the case and body). Luckily the screws that hold the ECU to the holding plate were insulated with the plastic fittings.
With ignition on this voltage drops to mv range. When switching off the ignition the voltage drops to around 0.5 volts and then after the, what i think is, the stepper motor has adjusted the volts then jump back up to 12 volts.
When the cover is grounded 1 of the relays in the MFU relay box is activated - I will let you know which one when I do some further testing today (Monday).
If i disconnect the small plug of the relay box then this removes the 12 volts when ignition is off and a mv reading when the ignition is on.
If the car is started and the diagnostics are connected the Lambda sensor does not go into closed loop (the original problem) when cold - i have not got it to temperature yet because of the ECU live case problem.
If have an MPI relay box but I think they are different - Is this correct?
Would i be correct in thinking that the relay box is suspect? even though I cannot work out how the ECU case becomes live from wiring diagrams. I have ohmed out between case and every pin on the ECU and there does not appear to be a connection.
Any help with this would be great 
Edited by R32Egor, 28 March 2022 - 08:09 AM.
