Technical Sei ECU permanent 12v/white engine relay question

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Technical Sei ECU permanent 12v/white engine relay question

Jan 8, 2021

I have a 126 with the 1.1 SPI from the Sei.

It has all the wiring loom, ECU, white engine relay etc from the donor car. The white relay I mean is the ECU, injector and fuel pump supply.

For a long time, the whole of the engine was wired to ignition live. This meant that the ECU would lose its learned modifications every time it was switched off, it was effectively being disconnected from the battery each time the ignition was switched off.

I have a bit of time on my hands now and have just changed the wiring to have the white engine relay be supplied with permanent live.

So far, so good. When the ignition is switched off, the relay keeps the power to the ECU (ECU pin 4 sinks current to allow the white relay to energise and supply pin 35 of the ECU from permanent live)....

For about 15 seconds only, after turning the ignition off. The relay then clicks over and power to the ECU is lost.

My question is, what would you expect this relay behaviour to be like typically? Should it permanently supply 12 V to the ECU when the ignition is off?

Or another question, how does the ECU keep power to keep its settings?

The car drives fine enough, but as you can imagine it's probably not optimal considering its doing it's factory learning on my drive to work every day!
I suspect it is pin 26 because in wiring 1.1 it is connected and it was not draining my battery. By modifying the wiring, in order to use the 1.4 16v with the control unit of the 1.2 16v, following the diagram, pin 26 is not connected. I, thinking that in any case it had no repercussions, I left pin 26 connected to +12 and instead I continuously discharge the battery, while with the 1.1 control unit it did not happen.
That's really interesting - thank you very much! I have just checked my spare 1.1 SPI loom and pin 26 is populated at the ECU (orange wire) which goes to both the white engine relay and the other grey/black connector which seems to connect the rest of the car to the engine bay loom.

My loom has been modified, but unsure if this part has been modified.

I'll connect it up and do some analysis, thanks again, you may have saved the job!
The relay switching itself off after shutdown is typical, once the ecu has saved its current state it will power down the main relay to prevent battery drain

When the ignition is switched on again the ecu wakes from I believe the code or fault light supply then latches the main power relay in again.