Code 16??

i have a b18c in my 89 4dr. its been converted to obd1 and uses a p72 ecu. when i did the swap, the cat didnt reach the mid-pipe, so today we made a pipe that fit. after i hooked up the exhaust, the computer now throws a code 16 and a code 41. code 41 say primary oxygen sensor-heater circuit overload, whats that? the code 16 says fuel injector system, defective fuel injector or unplugged.its not unplugged, and i dont see how it can be defective if it worked fine before i hooked up the exhaust. im thinking maybe take out the injectors and clean them?? any suggestions?