Oxygen sensor in Liana is of heated type which means, the sensor has a built-in heater element that heats the sensor up to operating temperature before it starts delivering data to the ECU. The operating temperature of O2 sensor is beyond 300 degrees (don't remember the exact temperature, it must be somewhere in the service manual).
Regarding your coil query, I bought mine for 9K from MontGommery Road. But don't go ahead and change the coils only because you suspect it. Take the spark plugs out and crank the engine to test spark on each coil one by one. If the spark is weak, only then replace the coils. If however the spark plug wires are leaking current, you can try with a new set of wires first.
Btw, could you explain "knocking"?