My brother is a tech in Sacramento. He is a test only shop. How many times have you worked on an engine trying to figure out a problem, and been wrong, only to find out it was something else after buying parts? Dead battery so you buy a new 1 only to find out that the alt was dead, or the regulator or the plug. There not there to fix your car, but to give you ideas. In fact, they are not really supposed to give you advise just for this reason. Ill give my brother a buzz real quick and see what he says to try, but he has always said that even some of the worst cars can pass with just a new cat. Only the cat may last 100 miles before dying due to problems that are causing the car to not pass to begin with.