1997 gt Starts then dies a few seconds after.

I bought a 97 mustang gt a few weeks ago and i got it to run once but now it will start for 2-3 seconds if the key is off then back on, will not start again if i crank after it dies without turning it back off. I replaced the fuel pump, ccrm, and pump was wired to a switch, i have spark while cranking. Whenever i turn the key on the anti-theft light never appears and theres no codes that i can read. Is it a PATS issue or something else?