I took off my test pipes, installed my stock cats, and still failed the smog test. I used this same method last year and was a success. Does anyone have any idea what the problem might be?

 

Shouldn't the smog tech or the report tell you what is out of specification and what mechanical or system problem will lead to it?

 

Not sure. You have the test results in front of you. I do not.

 

I would start by looking at all the results. when they inspected the car did it show any sort of obd-II codes being thrown. even if it doesn't trigger the cel light it might have logged some sort of issue that may be of use in diagnosing the problem. what year Z is your car? how many miles on the cats. any reason that they might have failed while were off the car (IE dropped or something that might destroy the catalyst matrix inside?)

any changes to the car since the last time that you had it inspected such as new plugs or injectors of something?

maybe sensors shot?

I'm not a mechanic so I can't tell you for sure whats wrong but this may help you find a place to start.

 

why don't you just ask them why you failed? That would make it alot easier to figure it out..

 

i failed the NO emission part of the test. 15mph 400 over and 25mph 250 over.