can I have 2 ECUs ?

[myfirstpicasso]

How feasible is having 2 ECUs: one unaltered/unmodified and the other one for experimental purposes. (of course not used at the same time but swapped when needed/wanted)
Apart from the technical difficulty of disconnecting and removing the ECU would there be any other challenges?

Both ECUs would be the same model and would be used on the same car. When performing the swap would there be need to do some sort of synchronization?
Are other control units on the car tied to a specific unique ID found in the ECU ? Could the new ECU be cloned 1:1 to match all the IDs in the first ECU ?

[wheeler]

Dont see why not.
You would need to either get the immo taken off the 2nd ECU or get the immo data cloned from your ECU onto it. Then it would be just a case of unplugging & swapping when required.

[GiveMeABreak]

You didn't mention what ECUs you are referring to which might help.

Regardless of cloning, you should also be aware that what is programmed in one ECU like the engine ECU, can update configuration options in the BSI for example, as configuration can be applied in several places but is updated collectively.

As for your other question, other ECUs (of which a car like this can have 20-30) are specific to the vehicle and most if not all ECUs will have specific configuration that is required for the specific vehicle / engine / options / equipment fitted.

[myfirstpicasso]

I mean having 2 Engine Control Units . The second one would be remapped for slightly more horse power (but this is just an example).
Would I need another pair of keyfobs or would it work with the same keys if the BSI is not changed?

(the car is Citroen Grand C4 Picasso 2.0 HDi 165 FAP Exclusive RHH 2011 but I'm asking in general and in principle at first)

[GiveMeABreak]

ECU is Electronic Control Unit to save confusion.

The fob transponder chip, Engine ECU and BSI are matched once paired. So if you cloned your Engine ECU as Wheeler suggested, then it will already be paired with the BSI and Transponder Chip in the Fob. So they should all still remain paired.

[liquidhandwash]

Sure I've got 2 for my 307 just order an ECU from HDI tuning with the immobilizer deleted. Just plug it in and you're done.
https://hdi-tuning.co.uk/

[wheeler]

Just remember you will initially need to set up the 2nd ECU first with things like injector coding, EGR position learning etc depending on functionality that your ECU has, also DPF soot/ash levels & additive levels. They will count down on whichever ECU is installed but when you swap the ECU over the usage of this stuff wont be correct.

[ozvtr]

Some BSI's require that the engine ECU acknowledge that it is "unlocked" before the BSI will do some of the "house work". An engine ECU with IMMO off may not acknowledge that it's unlocked. The engine ECU will run the engine but the BSI won't run it's ancillaries.
So "IMMO off" doesn't always work. Too many variables there. Might work, might not work.
Cloning the EEPROM is a better option.