Its usually bad fuel but false knock does happen. If it is false knock it sucks. Can be a pita to figure that one out.
If you really want to completely eliminate fuel once and for all then put 5g of race gasoline in there and log it. Check the stoich before you do it though and adjust the tune if necessary.
If you really want to completely eliminate fuel once and for all then put 5g of race gasoline in there and log it. Check the stoich before you do it though and adjust the tune if necessary.