Rebuilt engine won't stay started

[dsmdion]

So I just finished Dropping in the 7bolt for my talon, it fired up the first time no problems, but it wont stay started. Now when it starts it runs good for 5 seconds or so then it just kills. It doesn't run shitty or backfire or anything like that, it more or less seems like something is telling the car to kill itself so it does. The only way i can keep it started is if i physically hold the key in the cranking position, then i can keep it started (atleast it stayed the 2 times I tried it.) I pulled the plugs, and everything seemed normal, I pulled the high pressure side of the fuel rail, and fuel comes out, and I pulled and checked all the fuses out so im not sure what is going on exactly. Any ideas are helpful.