Abstract: An air/fuel mixture ratio learning control system for an internal combustion engine using a mixed fuel employs a learnt correction coefficient which is used both in a FEEDBACK mode air/fuel ratio control and in an OPEN LOOP mode air/fuel ratio control. The learnt correction coefficient is derived based on a FEEDBACK air/fuel ratio dependent correction coefficient per one of preselected engine driving ranges and per one of preselected concentration ranges of one fuel component contained in the mixed fuel. The learnt correction coefficient is cyclically derived in a preselected stable engine driving condition during the FEEDBACK mode air/fuel ratio control for updating a previously derived and stored one to minimize a deviation of the FEEDBACK correction coefficient from a reference value.

Abstract: An air/fuel ratio control system derives a air/fuel ratio dependent correction value for correcting a basic fuel delivery amount as a proportional-integral control value composed of a proportional component and an integral component. The proportional component is derived on the basis of an air/fuel ratio indicative signal which varies the signal level when the air/fuel ratio varies across a predetermined stoichiometric value. The integral component is derived on the basis of a basic fuel delivery amount which is derived on the basis of engine speed and an engine load.

Abstract: A method for detecting an intake pressure in an internal combustion engine which comprises detecting the intake pressure in the engine and at least one engine driving condition, variably setting a sampling period of the intake pressure to a sampling period, according to the engine driving condition, which is substantially different from a pulsation period of the intake pressure, sampling processing the intake pressure according to the sampling period set to set the value obtained by the sampling processing as a final detected value of the intake pressure, whereby the reliable sampling of the intake pressure is performed even if the intake pressure is pulsated.

Abstract: In an alcohol sensor failure detection system for an internal combustion engine, a failure of an alcohol sensor is detected utilizing an air/fuel ratio dependent correction coefficient during a FEEDBACK control being executed to maintain an air/fuel ratio of an air/fuel mixture at a target value with a fuel supply amount which is corrected by the correction coefficient. The correction coefficient is variable between predetermined maximum and minimum values depending on a monitored air/fuel ratio of the air/fuel mixture. When the correction coefficient is retained to the maximum or minimum value for no less than a predetermined time, the failure of the alcohol sensor is determined.

Abstract: An engine control system derives a basic fuel supply amount on the basis of preselected parameters including an intake air volume associated value and modifies the derived basic fuel supply amount in such a manner that the modified fuel supply amount becomes equal to the basic fuel supply amount derived on the basis of the preselected parameters when the engine is not in an acceleration state satisfying a predetermined first condition, and the modified fuel supply amount varies at a greater rate than variation rate of the basic fuel supply amount derived on the basis of the preselected parameters when the engine is in the accelerating state satisfying the predetermined first condition. The basic fuel supply amount as modified may be further modified with a correction value during the engine accelerating state satisfying a predeermined second condition.