i have bm328xi 2008 n52 engine it's been throwing codes P0420 P0430 with the service engine soon light in February I replaced catalytic converters and one of the O2 sensors and I replace the camshaft sensor and the crankshaft sensor and I replace the gasket valve cover because it was leaking and I replace the electrical water pump and the thermostat and I replaced a mass air flow sensor and from a month ago I did a smoke test and found two leaks so I put new seals did the test again no leaks were found
and I replaced the spark plugs and coils last year