why would there be a need to put a catalic converter on a 2011 subaru forester already?
http://auto.howstuffworks.com/question4822.htm ..says fouled spark plugs or bad exhaust valves. http://www.bobsmuffler.com/convfail.html and http://www.autoupkeep.com/QAexhaust.htm both say running too rich. Which fits, running too rich will foul plugs
Too much unburnt fuel entering exhaust stream
^^exactly. You could also have issues with the oxygen sensor(s) which can cause too much fuel in the air flow and result in the same issue with the catalytic converter. Additionally, if you have ever seen your check engine light on and your cruise light flashing, it was an indicator that something bad could happen to your CC.
Looking for a Used Forester in your area?
CarGurus has 19,839 nationwide Forester listings starting at $1,099.
Search Subaru Forester Questions
Subaru Forester Experts