MK Ganesan

i drive a C200 CGI-w204. for sometime now i realise that my car is not running smoothly at times. after running diagnostic test, it confirms cal 3 misfire. i have since changed the spark plugs. Battery is 75%. switched the coils and still we get the same fault code. i don't get rotten egg smell, which means the catalytic converter is ok. what should i do? i hate to assume that the injector is faulty with a car that is hardly 5 years and done 125000 kms.