In the fall and winter I have been experiencing some pretty bad spark knock when the motor is in lean burn. In my 2005 civic hybrid mt. Running 89 corrects this issue but mfy fuel mileage also drops from 42-44 to 37-40 I drive 150 mile round trip 5 or 6 days a week has anyone ran a colder plug? The 2006 calls for a colder plug than the 05. Dont give me the crap about honda knows best they use whatever plugs are around they don't design new plugs for every car.

 

try a bottle of red line cleaner in the gas tank. It's a detergent cleaner , most others are solvent based.