Starts then shuts off after three or four seconds

Okay, so here is a quick overview: I did an 8.1 swap Into my buggy, I have had my computer reprogrammed to take off emissions, and vats. I still have the two front o2 sensors, and two knock sensors. I am running a turbo 400 transmission. And it is drive by cable.

Now the problem:

It will start just fine but only run for 3 to 4 seconds and then shuts off. Backfires big time when you restart it.
It does not throw any codes.
It will run off of starting fluid.
The fuel pressure is up around 70
The pump cuts off and on like it’s suppose to

I am guessing it’s the injector pulse cutting off, how do I fix that or find out what’s causing that?

Thank you.
Brent