runs better with key off

The engine runs better with the key off. I have to pull the oil pressure switch off to kill the motor.

chry 273 GM tbi conversion

The return fuel pressure is approx 5 psi, I haven't checked pressure on feed side yet. It runs very rich with key on. smooths out some and not loading up with key off. The O2 sensors are not installed yet.

Any Help would be great