Try the GTP you can get it at auto zone run it through with a tank of gas I had the worst car the shop had ever seen ran that through passed with flying colors

There may be residual deposits in your exhaust system, go to O'Reilly auto or other parts store they have a liquid that can be added to your fuel it will catalyze and clean your exhaust system then your vehicle should pass. In fact the additive company guarantee that you will pass. Laurin