I have a check engine light on. Ford says it is catalitic converters. I, Ford and a performance shop have done an excellent job of fixing everything else that would send a false signal. Thermactors, timers, pump, vac leaks etc. I am in Phoenix area where it just passed emissions. The inspector pulled out their tester, turned the car off, said congrads, I passed. I turned the car on to drive away, when I turned on the AC the check engine light came on again. License, Im good for two years but why wait until it cost more. The car is mint with 120, 000 miles. Anyone know who has a complete used cat system off of their recent race car onverson? Does anyone have another thing I can check out? Thanks for reading this.