it's a real shame most ECMs we work with don't have a good way to enable closed loop just for specific operating ranges, so we can say 'closed loop when >2000RPM and >30KPA MAP', that way we can be open loop where closed loop just doesn't work properly.
If the code is accessible it can be modified.

I know this is off the OP question but if anyone knows where you can find factory open loop export bins for a 7.4 I would be interested to see how the factory went about it.
OEM open loop calibrations are known as "leaded fuel" or "export" calibrations. Look for CTS enable to be set high to prevent CL operation. I will locate an '86 5.7 cal for leaded fuel (7747) and post it for evaluation.