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I own an 04 SP23 and it has always burnt oil excessively, around 1-1.2L per 1000km (around a quart every 550 miles). There is no blue smoke coming from the exhaust and no evidence of oil leaks anywhere.

Ever since owning the car, it has always displayed a P0420 CEL, which when cleared, reappears 40km later with normal driving, however when taking it very easy on the revs it will come back after a longer time than usual. The code is a cat/o2 sensor code so it is plausible that the oil burning may have triggered that too, not sure.

Doing some forum searching, the most common issue is a blocked PCV valve and the excessive oil burning causes the Cat to plug and fail, hence no smoke. However other causes may be worn valve stem seals, worn valve guides or rings (which im hoping is not the case, Im not in the best position financially to fix a repair of that magnitude)

A couple of weeks ago i added a bottle of Rislone stop smoke to the oil (as a temporary bandaid to see if would help). It didn't change anything and it seems it has created a ticking noise (like pencils on a desk) coming from the engine. I still have no idea whether this is valvetrain related or injectors or what it could be.

The oil goes black very quickly and smells sort of like fuel (within 1000km)

I checked the sparkplugs and found they had white ash deposits and needed replacing asap. Has anyone solved the oil burning issues with a new pcv valve? What else can I test aside from doing a compression test, which i have yet to do? Has anyone had similar issues and have solved them/figured out what caused them?
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