Question about open loop

Just completed a 2005 5.3 swap on a 86 chevy truck. I need to drive it to the exhaust shop without O2's and with open exhaust. I got it fired up and everything looks good but my fuel trims keep going way negative then when I accelerate it falls flat on its face until I let off the throttle.

I set LTFT enable to max temp but I still see closed loop kicking in, STFT's keep going negative and LTFT's are staying at 0. Still falls on its face when I accelerate UNLESS I keep doing a fuel trim reset using DVT (literally have one finger on the mouse clicking it once a second)

So how do I disable any and all fuel trims until I can get the exhaust and O2's on it? Seems like a rookie question but I'm stuck. So what is the configuration for open loop?

Maybe I’m getting LTFT enable temp confused with Closed loop enable temp? Are these two different setting? Is this why STFT’s are still messing with my fueling (despite having no o2’s hooked up which doesn’t make sense to me)

Just reviewed scan data and without O2’s hooked up they are both showing 1107mV. Does that mean the pcm thinks it’s rich and is pulling fuel?

It sounds like the O2 sensor signal wires are shorted to power, or the ECM has failed.

Well with both o2’s hooked up after exhaust I have proper fluctuating O2 voltage. Not sure why this engines does this. I’ve drive to exhaust with out O2’s before and no problem.