1996 Integra GSR with LS/VTEC Swap: PO141 Code Appears Only with Stock ECU (P72 OBD2A)

Model: 96 GSR Integra Fault Code: P0141 Posted: 2012-02-29 22:40

Hi, I have a 1996 Integra GSR with an LS/VTEC engine swap. Currently, it's equipped with a chipped P28 OBD1 ECU, no catalytic converter, and no secondary oxygen sensor. The vehicle does not throw any error codes when running with the P28 ECU. However, when I revert to the stock ECU (P72 OBD2A), the vehicle begins throwing a PO141 code. I have a bung installed in the race pipe to accommodate a secondary oxygen sensor. My question is: does the vehicle require a catalytic converter for the PO141 code to be cleared or for the system to function properly? Or can I simply install the secondary O2 sensor and eliminate the code without a cat?