An engine control unit of a multi-fuel is provided. The engine consumes a mixture of a first fuel and a second fuel. The engine control unit includes hardware circuitry that includes one or more processors configured to calculate an autoignition delay of the mixture of the air and the second fuel based on current operating conditions of the multi-fuel engine. The one or more processors also are configured to calculate an upper limit on an amount of the second fuel that is supplied to the multi-fuel engine based on the autoignition delay that is calculated.

Methods and systems are provided for converting an asymmetric sensor response of an exhaust gas sensor to a symmetric response. In one example, a method includes adjusting fuel injection responsive to a modified exhaust oxygen feedback signal from an exhaust gas sensor, where the modified exhaust oxygen feedback signal is modified by transforming an asymmetric response of the exhaust gas sensor to a symmetric response. Further, the method may include adapting parameters of an anticipatory controller of the exhaust gas sensor based on the modified symmetric response.

Methods and systems are provided for converting an asymmetric sensor response of an exhaust gas sensor to a symmetric response. In one example, a method includes adjusting fuel injection responsive to a modified exhaust oxygen feedback signal from an exhaust gas sensor, where the modified exhaust oxygen feedback signal is modified by transforming an asymmetric response of the exhaust gas sensor to a symmetric response. Further, the method may include adapting parameters of an anticipatory controller of the exhaust gas sensor based on the modified symmetric response.

Disclosed herein is a method for diagnosing and controlling a two-step exhaust variable valve lift (VVL) system, including: a controlling device acquiring an operation state signal of a vehicle; when the vehicle is in the over-run state, the controlling device outputting a mode conversion signal of the two-step exhaust VVL system; an air mass sensor measuring an air mass entering an engine, and the controlling device comparing a predetermined prediction value of the air mass with the measured air mass; when a difference of the compared air mass corresponds to a predetermined mode conversion comparing amount, the controlling device determining that a mode conversion of the two-step exhaust VVL system is completed; and when the difference of the compared air mass does not correspond to the mode conversion comparing amount, the controlling device determining that the two-step exhaust VVL system is faulty and outputting a result thereof.

Systems and methods for determining fuel delay in a fuel injected engine with cylinders that may be deactivated are presented. In one example, the fuel injection delay is determined via a cylinder firing schedule array when the cylinder firing schedule array is available. The fuel injection delay is determined via weighted average of a fuel injection delay of a present engine cycle and a fuel injection delay of a past engine cycle when the cylinder firing schedule array is not available.

A system includes a controller that has a processor. The processor is configured to receive a first signal from a first sensor indicative of a first exhaust measurement, wherein the first sensor is disposed at a catalytic converter system inlet of a catalytic converter system. The processor is further configured to derive one or more of an estimated length, estimated volume, or estimated transport delay of an exhaust conduit based on the first signal, wherein a first end of the exhaust conduit is connected to an engine outlet of a engine, and a second end of the exhaust conduit is connected to the catalytic converter system inlet; and to apply the one or more of estimated length, estimated volume, or estimated transport delay of the exhaust conduit during control of the engine.

A method for monitoring an exhaust gas sensor coupled in an engine exhaust is provided. In one embodiment, the method comprises indicating exhaust gas sensor degradation based on a time delay and line length of each sample of a set of exhaust gas sensor responses collected during a commanded change in air-fuel ratio. In this way, the exhaust gas sensor may be monitored utilizing robust parameters in a non-intrusive manner.