2005 Sierra 1500 SLE Z71 L33
I have an L33 engine. Vortec 5300. Gasoline. 87. But recently when I've been idling there in traffic or backing into my driveway, (especially) there is such a foul diesel engine smell. Reminds me of the school buses pulling off. I do have a P0430 (catalyst efficiency low, which side? idk I forgot). I have replaced my knock sensors twice now, most recent time last year, which means that yes the intake gaskets have been moved around a bit, but I don't believe there's an issue (yet). I will be probably removing them again soon to replace them, but this smell is brand new, so I ask what I couldn't really find anywhere, what causes that diesel smells from a gasoline engine?