I failed smog and I went to my mechanic. He said it was the catalytic converter but I didnt want to pay $400 for the obd 2 converter so I had him put in the cheaper OBD 1 converter in. Got it tested and passed smog but then my check engine light came on. Mechanic said this would probably happen but how can I get the check engine light to go off. Also now the speedo goes crazy sometimes. Mostly when i take my foot of the gas will go up to 90mph then down to 20mph. what could be causing the wacky speedo. Please help. Thanks.