i just got off the phone with the mechanic and accdg to him the primary fuel pump really needs to be replaced. there's power in it but motor wont run. he said to check the fuel filter, high pressure pump, rail pressure and injectors is quite irrelevant since circulation starts from the primary pump, though they are all fine including the sensors as per him. but the thing is, after replacing the pump and it still acts up, they'd need to diagnose the other said components. is this correct in you opinion?