Methods and systems are provided for diagnosing a variable displacement engine. In one example, a method includes during steady-state vehicle cruising, operating an engine with one or more cylinders of the engine deactivated, commanding the one or more cylinders to reactivate, and indicating cylinder valve actuator degradation responsive to a fuel usage change following the command to reactivate.

A method of exercising a generator includes detecting a temperature of the generator, if the temperature is above a predetermined temperature, activating a starter motor and starting an engine of the generator, and performing a first exercise test, and if the temperature is below the predetermined temperature, activating the starter motor without starting the engine of the generator, and performing a second exercise test.

A method for verifying a CVVD location learning result may include performing a learning value verification control by confirming a position of a control shaft connected to a motor with a signal value of an auxiliary cam sensor for a rotation of a camshaft if a controller determines that a learning value acquired in a short duration and a long duration of a CVVD system is desired to be verified.

A method for recognizing a state change of a fuel injector of an internal combustion engine, in which fuel from a high-pressure accumulator is injected into a combustion chamber with the aid of the fuel injector. A value that is representative of a static flow rate of fuel through the fuel injector is ascertained. A state change of the fuel injector is deduced when the representative value differs from a comparative value by more than a first threshold value.

An electronic control unit of an internal combustion engine is configured to control the fuel injection valve and to control a spark plug if necessary such that fuel is combusted by pre-mixture compression ignition combustion or flame propagation combustion. The electronic control unit is configured to perform homogeneous combustion in a flame ignition operation range when switching failure has not occurred, the homogeneous combustion being combustion in which fuel homogeneously diffused into the combustion chamber is ignited using the spark plug and is combusted by flame propagation combustion. The electronic control unit is configured to perform spray-guided stratified combustion in a second operation range when the switching failure has occurred, the spray-guided stratified combustion being combustion in which fuel in the fuel injection path is ignited using the spark plug and is combusted by the flame propagation combustion.

Various embodiments include a method for detecting deviations occurring in the valve drive of an internal combustion engine comprising: measuring dynamic pressure oscillations of intake air in an air intake tract of respective internal combustion engine during operation; calculating an inlet valve stroke phase difference and/or an outlet valve stroke phase difference based on the measured dynamic pressure oscillation; calculating a valve stroke phase deviation value with respect to a valve stroke phase reference value based on the calculated phase difference; and calculating a first valve drive deviation value based on the valve stroke phase deviation value.

Disclosed are a method and apparatus for diagnosing a fault in a CVVD system. The method includes collecting information necessary to determine whether a fault diagnosis mode entry condition of the CVVD system is satisfied, determining whether the fault diagnosis mode entry condition is satisfied based on the collected information, calculating prediction duration corresponding to a current engine RPM and manifold pressure when the fault diagnosis mode entry condition is satisfied, calculating current duration based on an output value of a motor sensor for detecting the RPM of the duration control motor of the CVVD system, comparing the manifold pressure-based prediction duration D1 with the sensor output-based duration D2, and determining an error of the motor sensor or whether the CVVD system has failed by comparing a duration difference cumulative value, that is, a cumulative value of difference values between the D1 and D2, with a previously stored threshold.

A method for diagnosing a purge control solenoid valve (PCSV) may include forming a negative pressure in a fuel tank, checking a pressure in the fuel tank and determining whether a target negative pressure is generated, when the target negative pressure is determined not to be formed based on a result of the determining whether the target negative pressure is generated, suspecting a stuck of the PCSV that electrically controls an inflow amount of evaporated gas from the fuel tank to an intake system of an engine, and increasing a purge amount of the PCSV.

A method and apparatus for diagnosing an engine system are provided. An apparatus for diagnosing an engine system including a continuous variable valve duration (CVVD) apparatus according to an exemplary embodiment of the present invention may include: an accelerator pedal position detector configured for detecting a position of an accelerator pedal; a brake pedal position detector configured for detecting a position of a brake pedal; a vehicle speed detector configured for detecting a speed of a vehicle; an intake pressure detector configured for detecting an intake pressure; and a controller configured for determining whether a fuel cut condition is satisfied and determining whether the CVVD apparatus is in a failure state when the fuel cut condition is satisfied.

Methods and systems are provided for diagnostics of a cylinder valve actuation mechanism in a variable displacement engine (VDE). In one example, during an engine-off condition, the engine may be rotated unfueled, via a starter motor, and a reference exhaust air flow may be estimated. One or more deactivatable engine cylinders may then be deactivated and degradation of the cylinder valve actuation mechanism may be indicated based on a difference between the exhaust air flow following the cylinder deactivation and the reference exhaust air flow.