Methods and systems are provided for operating a split exhaust engine system that provides blowthrough air and exhaust gas recirculation to an intake passage via a first exhaust manifold and exhaust gas to an exhaust passage via a second exhaust manifold. In one example, exhaust from a first set of exhaust valves coupled to the first exhaust manifold may be selectively routed to the intake passage via each of a first EGR passage coupled to the intake passage upstream of a compressor driven by a turbine and a second EGR passage coupled downstream of an outlet of the compressor. A decision of whether to route exhaust gas to the intake passage via the first EGR passage, second EGR passage, or both passages may be based on engine operating conditions.

A control apparatus for an internal combustion engine includes a turbocharger, a bypass passage, a waste gate valve, a turbo bypass valve, an air-fuel ratio sensor and an electronic control unit. The air-fuel ratio sensor is provided in an exhaust passage downstream of a merging point at which the bypass passage merges with the exhaust passage. The electronic control unit is configured to, when a predetermined acceleration request is established and a required opening degree of the turbo bypass valve is larger than a predetermined reference opening degree, execute air-fuel ratio control for changing an air-fuel ratio of exhaust gas from the internal combustion engine for a predetermined first period, and close the waste gate valve based on a convergence status of detected air-fuel ratio fluctuations. The detected air-fuel ratio fluctuations are fluctuations in air-fuel ratio that is detected by the air-fuel ratio sensor resulting from the air-fuel ratio control.

A method for diagnosing a no-start fault of a vehicle push-button start system including a push-button switch, where the system starts a vehicle engine if the switch is pressed and a vehicle brake is applied. The method includes detecting that a no engine crank condition has occurred if the switch is pressed and the brake is applied, and if so, performs a no crank diagnosis. The method also includes determining that a starter control relay has not been enabled after the system is in a crank power mode, and if so, performs a starter not-enabled diagnosis. The method also includes determining that the starter control relay has been disabled before the engine is running, and if so, performs a start disable diagnosis. The method also includes determining that the engine has stalled within some minimum time after it has successfully been started, and if so, performs an engine stall diagnosis.

Systems and methods for determining operation of a cylinder deactivating/reactivating device are disclosed. In one example, a warm engine is rotated without being supplied fuel to determine the presence or absence of valve actuator degradation. Degraded valve actuators may be determined when there is a lack of a temperature rise in the engine exhaust system.

Methods and systems for evaluating whether or not a fuel amount that is greater than a threshold has been release to an engine via fuel injectors when the fuel injectors are commanded off are presented. In one example, an oxygen sensor is activated and engine cranking is prevented until a pumping current of the oxygen sensor is proportionate to a concentration of oxygen sensed via the oxygen sensor so that released fuel may be observed during engine starting.

A method for starting a gaseous fuel internal combustion engine is disclosed. According to the disclosed method, the engine is rotated using a start device until a first speed threshold is reached. After reaching the first speed threshold, pilot fuel is supplied to a plurality of cylinders of the engine to combust the same. After performing an ignition health check, gaseous fuel is supplied to all or a relatively large number of cylinders to start accelerating the engine up to a second speed threshold.

An air flowmeter is arranged in an intake passage. An air-fuel ratio sensor is arranged downstream of an addition valve in an exhaust passage. An estimated air-fuel ratio is calculated based on an intake air amount detected by the air flowmeter and the sum of a fuel amount injected by a fuel injection valve and a fuel amount added by the addition valve. It is determined that there is a stuck-closed anomaly in the addition valve if the logical conjunction is true of a condition that a detected value of the air-fuel ratio sensor is greater than the estimated air-fuel ratio by a margin greater than or equal to a specified amount and a condition that a detected value of the exhaust temperature sensor in a period in which the addition valve adds fuel is smaller than a reference value in the period by a margin greater than or equal to a predetermined amount.

Systems and methods for diagnosing the presence or absence of turbocharger wastegate degradation are presented. In one example, an intake manifold pressure sensor provides a basis for determining whether or not turbocharger wastegate degradation present. The turbocharged engine may be rotated in a reverse direction to assess wastegate degradation.

Methods and systems are provided for diagnosing the functioning of a variable displacement oil pump. In one example, a method may include commanding a change in displacement of the variable displacement oil pump during a vehicle keyed-off condition and diagnosing a degradation of the oil pump based on a corresponding change in an estimated crankcase pressure.

Methods and systems are provided for diagnosing whether active engine mounts configured to isolate engine vibration from a cabin and chassis of a vehicle are functioning as desired. In one example, a method includes indicating degradation of an active engine mount by inducing degraded combustion events in a preselected engine cylinder, and operating the active engine mount in multiple modes, the indication responsive to an amount of vehicle chassis vibration during each of the modes. By monitoring chassis vibrations as a function of induced degraded combustion events, and further responsive to the active engine mounts being controlled to the multiple modes, it may be indicated as to whether the active engine mounts are functioning as desired.