My 1988 Toyota Supra has failed emissions test twice and that is after installing a new converter. They say the Carbon Dioxide levels are six times over the legal limit as well as Hydro. The Nitrous oxide is fine. What could be causing this? We just bought this car and I assume it has been souped up as it is loud and tough sounding but I am no car person.

Thanks!

This is just a guess, but does it have an aftermarket cold air intake?

Did you buy the cat from a Toyota dealer or is it an aftermarket no name brand?

As a matter of fact, yes... what does that mean?

and we bought the car from a private owner for our daughter

CAI's tend to do that for reasons I do not know why. If you still have the stock intake it'd be wise to reinstall it to go get your emissions rechecked. In Cali, we have a CARB (California Air Resources Board) sticker that comes with CAIs and to pass emissions the inspector uses that # so that emissions can be passed, not sure if there is something similar in TX. Maybe contact the previous owner to see if he still has the stock intake?

Also, aftermarket cats aren't compatible with Toyotas for some reason, they only play well with OEM parts. So in future, if you decide to change out plugs, wires, etc. stick with NGK or Denso branded parts you get from your local dealer or online such as rockauto.com.

What guys around here do is just fuel up with E85 which burns clean and then go do the emissions test, your car will run like garbage if its tuned for standard fuel but you'll pass emissions :)