I have had my Hyundai Matrix for 5 years now at 200000+km. I was surprised that she barely passed the emissions testing after revving it up for 3k+ rpm considering that I have cleaned the tailpipe, something that I have done for years now.

Recently, I have been observing that the exhaust smells "sulphuric" especially on cold starts, which my cousin told me when he opened up our gate. There is a grayish smoke coming out from the tailpie and the smell feels heavy on the lungs. Whenever I rev up to 3k rpm especially on inclines, I can now see from the rear view mirror the belching.

She has a history of Ondoy flooding by the way. I didn't have any ECU problems though according to the casa and the engine didn't have any rust build-ups.

Where should I have her diagnosed? Diesel shops that you could recommend?