It sounds to me like your massive negative fuel trim is likely due to the PI. I used to run a throttle body injection (TBI) ring which was a waste of time. It would activate using a 15 psi Hobbs switch- I would always get huge negative trims as a result.
The strange thing is I'm told it is activating at the right RPM. The problem is, trying to decipher this AIC map is a little more difficult than my little brain can handle apparently. Judging by my calculations, with the n20 map sensor and whatever else goes into that, I thought it could be enabled a bit sooner but like I said, I'm told the lean to rich spike was due to lack of fuel at that RPM and not the activation RPM. I've seen some logs with pressure bouncing around, sometimes in completely acceptable range, but am told the resolution of that sensor doesn't tell the whole story hence my desire to log it properly with something external. I also did a dumb and chose 72# injectors as well, so that likely doesn't help. I haven't actually touched this problem on my car for a year and a half, so lots of these details are far from fresh.
@RabbitOLychee
Aside from not enough fuel on startup, you may want to consider leaky injectors. But assuming it's not that, if you have a leak as was suggested above, this would allow air in the pressurized line and would create a stumbling problem.
Less likely to be your issue, but some aftermarket fuel controllers don't blip the pump at key-on and therefore don't build pressure correctly. Some after market pumps don't have a 1-way valve, so all the primed fuel just leaks back into the tank.
Thanks
