98 saturn sc2 problems runing

well we just put a new motor in it and we got it started but she only runs for 9 secs we hooked up obd tester to it and ran diagnostic on it and all that comes up is the time she runs and engine stall with no code and she makes a weird poping noise after she stalls I thought it was injectors goin out but there good so..... idk anyone got ideas?