My car starts up but won't stay running, it will idle for a few seconds and then cut off. I'm not sure what it could be any suggestions?

Hi Im new to the forum, having some troubles with my engine swap. So I bought a 95-96 eclipse gst engine for my 97 gst (my husbands mistake). We have it all hooked up but it wont start up. It just cranks but wont turn over completely. I have been reading some about the cas being different? Im...