Decat info -for what it is worth here is my
two cents worth.
If there are no post cat sensors then removal of the cats will not cause any lights or running issues.
The pre cat sensors are the only ones to tell the ECU to adjust mixture.
The post cats are only for emmisions reading.
I have a V6 CF2 car that has two precat sensors [one in each downpipe] and I removed the cat and had a resonator installed in its place.
I now get a regular extra 50kms per tank and a marked increase in performance.
This is the best mod I have done to date.
We have no emmisions testing here in NZ but if we did it would be worth the cost [I would redeem that in mpg] and effort to have it removed and replaced between tests.
IMHO cats are a waste of space and if you consider how much extra fuel it takes to travel the extra 50kms with the cat in it makes a joke of the enviromental "gains".
Then multiply this by the number of cars in the world with cats.
There also remains the issue of disposing of the casogenic cats at the end iof their useless life.