Passive evaluation of event delay assignment for individual cylinder fuel/air ratio control

A fuel and emissions control method for an internal combustion engine of a vehicle, the fuel and emissions control method comprising:

• providing an upstream oxygen (O2) sensor arranged upstream or before an exhaust treatment system of the engine, the upstream O2 sensor being configured to generate an O2 signal indicative of a level of O2 in exhaust gas produced by combustion of fuel/air mixtures within each of a plurality of cylinders of the engine;
• providing a controller configured to perform individual cylinder fuel control (ICFC) closed-loop control of the engine including determining an ICFC multiplier for each cylinder of the engine to obtain a plurality of ICFC multipliers, each ICFC multiplier indicating a multiplier for a base fuel/air ratio;
• and
• performing, by the controller, passive evaluation of the plurality of ICFC multipliers including:
• determining, by the controller, that a particular ICFC multiplier of the plurality of ICFC multipliers exceeds an ICFC multiplier threshold indicative of a ICFC multiplier that will be evaluated at a desired frequency;
• in response to determining that the particular ICFC multiplier exceeds the multiplier threshold, determining, by the controller, first and second cylinder fuel-air (FA) imbalances during first and second passive evaluation stages, respectively, separated by a passive evaluation delay period;
• and
• based on a comparison between the first and second cylinder FA imbalances, either (i) passing, by the controller, the passive evaluation and maintaining, by the controller, the plurality of ICFC multipliers or (ii) failing, by the controller, the passive evaluation and (a) resetting, by the controller, the plurality of ICFC multipliers and (b) increasing, by the controller, the passive evaluation delay period and repeating the passive evaluation.