Omega B Y25DT – Start problems, return quantity?

Hello everyone, my Omega is having some funny problems: In the cold start the engine does not cause any problems, it goes through powerfully after two turns, even at the prevailing temperatures and runs immediately round. If the car is still cold, I can turn off the engine and start again without any problems, even several times in a row. But if the engine is warm, it doesn’t want to start up any more. I have to help with the start pilot then the engine starts immediately and runs immediately round. The FOH wants to replace the injectors, or the whole injection pump, but that’s economical nonsense and probably not necessary. Can anyone help? Maybe some sensor only needs to be replaced?? I am grateful for every tip. Thank you in advance DrBig