Going from cat-less to catted. Tune required?
 

This is pretty much a general question about tuning, not exactly specific to the FRS/BRZ.

I'm getting a used car which was cat-less and did not pass emission standards so the previous owner put on a cat. Cat is on the downpipe.

Do I need to get it tuned? From what I've read, when going from catted to cat-less, you need a tune but I dont know if its necessary the other way around.

The car is a '97 Audi A4 1.8T if that matters.

...yeah....I'm gonna have to say to repost this to the "other vehicles" section...

:Bill Lumbergh's voice:

I was going to but it seemed like the other section seemed more General than technical, and that others who are going from cat-less to catted in the FRS/BRZ could benefit.

Mods please move if its in the wrong section.

Vortex ---------> that way

Was it tuned to begin with? Is it possible that the car wasn't tuned and therefore couldn't pass emission? Sounds like to me you'll be putting it back to how it should be.

It was tuned, but with a moderate tune. The previous owner said it should run better with a cat, and that a re-tune is not required..I'm not sure of the reason why though....

It will more than likely need a tune because the sensors may have been turned off and possibly the a/f ratio may be off. I would get it retuned just for piece of mind knowing that it was tuned for what you want...but in short go to vwvortex and be careful with the 1.8 they are known to have issues...

Not sure about those but sometimes catless downpipes will cause boost spikes or other issues.

But yes vwvortex has plenty of info.