It is interesting to troubleshoot purely on symptoms, but it is also a
bit stumbling in blind. Some measurements as discussed earlier or some
faut codes would be helpful.

Last time we cocluded, that the cold start valve was erroneously
energized when i shouldn't, from the fact that the car ran fine with
the cold start valve disconnected. This is apparently not the whole
story.

If it really does some difference to disconnect the cold start valve,
it also means that it is actually energizing, where it should not,
which leaves the fuel pump relay as prime suspect.

Assuming this is right, we have to look for, what else goes wrong.
Bearing in mind that the fuel pump relay contains a logic circuitry to
control various things including fuel pump and cold start valve, it is
possible that it not only tells the cold start valve to operate
incorrectly but also the fuel pump. So, are you sure, that the symptom
now (with cold start valve disconnected) is flooding and not starving ?

Anyway, if above is true, it puzzles me that the car still runs with
OVP relay disconnected. If cold start valve floods the engine with OVP
relay connected (ECU operative), it should also flood it with OVP relay
disconnected (ECU inoperative), unless the mixture by coincidence
remains within acceptable limits.

So if above track is wrong, my next suspect would be the EHA
(electrohydraulic actuator), which is located on the backside of the
fuel distributor. This unit adjusts the fuel pressure to the injectors
according to the ECU control signals, as previously described (earlier
I did not realize, that the fuel pressure regulator, you talked about,
was the regulator for the pressure input to the entire injection
system).

I recently had a fault in it, which caused flooding always, so the
engine wouldn't even start.