A middle deck of a cylinder head having a partition that separates the exhaust and suction sides thereof to make the engine oil flow longer at the exhaust side having a greater area adjacent to a water jacket and cool off to a required level of temperature by enlarging the radiation area with a plurality of radiation protruders. The insulative housing includes a base portion and a tongue extending from the base portion. The value of orifice size change can be used for both diagnosing injector deterioration and compensating fuel flow rate in a feedback control.