1966 250SE Coupe
Most modern electronically fuel injected cars have a system that primes the fuel pump and pressurized the system, by briefly turning on the fuel pump, when you rotate the ignition key to the "on"/"run" position. Then, if no input is received from the distributor, or in some cases, engine oil pressure, or flywheel teeth movement, the pump immediately shuts off. This is to prevent the pump from running after a crash, and causing a fire. My suggestion would be to connect a volt meter to the pump, and check to see if you have system voltage during engine cranking.