Method for determining amount of fuel injection in engine system

A method for determining the amount of fuel injection in an engine system having a crank sensor and airflow sensor, comprising the steps of:

• computing a speed change of engine revolutions per minute by detecting said engine revolutions per minute from a crank sensor;
• computing a speed change of an intake-air amount by detecting said intake-air amount from an airflow sensor;
• comparing the speed change of said engine revolutions per minute and the speed change of said intake-air amount with reference values, respectively, and then deciding whether a diagnosis of generation of vibration and reverse-flow in an intake manifold is required;
• if diagnosis for generation of the vibration and reverse-flow in said intake manifold is decided to be performed, executing a pre-established logic for determining the vibration and reverse-flow and then deciding whether the vibration and reverse-flow are generated in said intake manifold;
• if the vibration and reverse-flow are determined to occur in said intake manifold, correcting said intake-air amount, which is restored before the generation of the vibration and reverse-flow, in response to a present engine speed and computing a present intake-air amount;
• and
• deciding a fuel injection amount by using the above computed intake-air amount instead of using said intake-air amount measured by said airflow sensor.