what car, what year /model ?
I had problems with the E30, M40 engine, where a short fuel hose (6 cms)
runs over the head, between the fuel inlet pipe and the injectors.
Every two or three years the rubber dries and cracks. The fuel is leaking
for one minute or two just after the key is turned on. Then the pressure
decreases and everything runs fine. Difficult to troubleshoot because gas
evaporates quickly, especially on this very warm part of the engine.
I'm used to replace it on a regular basis !

Hope this will help you