After everything was back in place, I tried to start the car while switched to petrol, but it turned out that previous owner (a dickhead that calls himself a "Citroen expert") didn't use petrol to drive the car since he fitted it with LPG.

He told me that "car doesn;t have a fuel pump since it got broke only 2-3 days after selling", but the truth is that pump was removed on purpose - LPG was fitted in such way, that when car works on LPG it still continues to use petrol! To put it simple - the car was mixing petrol and LPG. That was the reason to put a relay that turns off fuel pump when car is switched to LPG.
Here you can also see a 10A fuse - it protects the fuel pump and ignitoion relay in case of short circuit. Interesting thing is, that Peugeot 405 has this fuse but BX doesn't.
Many other things were changed - ignition coil, camshaft sensor, monopoint was cleaned in ultrasound tub, air and water temperature sensors were changed; all four Ferodo brake discs, brake pads (TRW Lucas in the front, Textar in the back), oil filler hose, new CV joints and bellows, new summer tyres (Tigar 165/70 R14), and of course TZI wheel covers ("The pills", as we call it here).

I wish I could do more, but I don't have enough "time" (money) as we like to say here.
And one more picture, with my friend's Pallas made of 19 TZI:
