A popular modification to our Subaru's is the fitting of a 'Sports' catalytic converter. Manufacturer's advertise performance increase and still the ability to pass the annual MOT emission tests in the UK. For those people out there failing your emissions with a Sports CAT or a failing CAT you may find the procedure below might get you through.
CAT Failure Procedure
First a note on what may be wrong:
- the Lambda sensor could be faulty. This will need to read correctly, otherwise the CAT will fail the MOT.
- the Lambda reading could be out because of a leak in the exhaust, and that will put the CO up.
- the Lambda should read between approx .97 and 1.01 for a pass.
After first checking the exhaust system for leaks try pulling one plug lead off the engine and revving it up (30 seconds or so should do). The unburnt fuel will be thrown into the cylinder at the most 200ccs per stroke, and each of those strokes is going to throw it through the exhaust, then the turbo and then into the CAT. The fuel is being evaporated and burt in stages throughout. It hits the CAT membrane and this causes a catalyst which makes the fuel burn so rapidly and hot it removes all traces of CO.
Now re-attach the plug lead and go for the test!
Note: PLEASE make sure you turn the ENGINE OFF before unplugging and plugging in.
Information Source - SIDC Forum thread, Help! My My00 With Scoobyworld Sports Cat Failed Mot!