I tried to smog my 91 turbo the other day, but it didn't pass. It failed the NOX portion of the test. At 15 mph, 1977 rpm, the NOX was 975. Passing would be 799. At 25 mph, 2106 rpm, the NOX was 814. Passing would be 738. My guess is that I need a new Catalytic Converter. What do you guys think? If I do need a new cat, what kind should I get?