being you have a 02 and no cat i believe, you said silencer? wrong terminology for what ever part you mean. will set the rear o2 code, as its failing the cat test and over fueling and that might be burning up your o2 sensors.
heater element's go bad, replace the sensor, use only delco sensors, no idea what brand you used but aftermarkets are not always so good and can fail or not work right.
if you have no cat you can try a simulator thing, or a pair of bungs to pull the o2 out of the pipe to trick it to read right.
