when the fuel pump's dead.
We were megasquirting a miata, and we had it running for a minute or two. Once it warmed up we had to turn it off and wire in fan control. After that it would only start and die, every time. we put gas in it, no go. later, the guy shorted some circuit in his stock AFM (he stock ECU was removed, though), and the fuel pump started working...
Now my friend is convinced that the manifold vacuum was somehow sucking in fuel from the injectors...
I told him that's impossible, there's no way there's enough vacuum to suck fuel passed the injectors that are only open for 5 ms, even less to pull the fuel passed a dead fuel pump along with that...