The 15 mph test is at a higher load than the 25 mph test, making the cat work harder. My cat was the problem. I got the carsound obd2 carb/epa approved cat and passed with almost zero emissions.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
Team B.O.B.® - Ballaz on a Budget