From the F series Wikipedia page which took me all of 30 seconds to find...
- ULEV engine uses 32-bit ECU with individual cylinder air-fuel ratio control, lean air-fuel ratio during fast idle, high-efficiency catalyst and low heat-mass exhaust system
and
F23A4[edit]
This engine was used in the 1998-2002
Honda Accord ULEV models. It is substantially similar to the F23A1, but features
ULEV certification with a slight reduction of power: 148 hp (108 kW) with a maximum torque of 150 lb·ft (203 Nm). This engine has a different exhaust manifold, a more restrictive intake manifold and cylinder head, and a 32-bit ECU that uses an AFR (Air Fuel Ratio) oxygen sensor when compared to the F23A1.
Sounds like the ECU is specifically geared towards the ULEV motor and it's characteristics which could potentially run a different motor worse.
I don't really mess with OBD2 stuff or accords often but I would suggest finding an ECU for a car same year as yours but non-ULEV and try that and swapping to a non-ulev O2 sensor.