This crops up quite often and I usually refer to the fuel system cleaner we use at work which is produced by FORTE. Yesterday a 1996 Honda Civic (you would normally expect to pass the BET test) failed the full cat test. Results as shown. The owner went home with a bottle (400ml) of Forte fuel system cleaner in the tank. When he returned today he had only covered 20 miles. You can see for your self the difference it had on the emissions as the car passed today on the BET test with very low emissions. This post was edited by a mod using 2 x ENTER (as it was a total balls up as was) and took seconds. Please try harder.