I agree 100% but in my case I think that when the truck starts to run bad at start up and backfire through the intake wouldn't that indicate a lean condition?Buzzbass said:YES ! Cats go bad for a reason. Usually it's bad front O2 sensors. They make it run pig rich, which in turn fouls the cat(s). O2 sensors should be changed out every 60-70K miles as a wear item. At least the front 2 anyway, they're responsible for setting your A/F mixture.