Methods and systems are provided for coordinating cylinder deactivation adjustments with changes to individual cylinder piston displacement. In doing do, the benefits of variable displacement and variable compression ratio may be synergized. An engine can be operated with some cylinders deactivated while active cylinders operate with knock addressed while spark timing is at MBT for a longer duration.

Methods and systems are provided for addressing spark plug soot fouling. In one example, a method may include alternating one or more combustion events with spark timing advanced with one or more combustion events with nominal spark timing. The approach allows spark plug over-heating, and related issues such as knock, to be reduced.

A spark control module, for an engine speed and an engine load: for a first predetermined period, supplies spark to each cylinder of the engine at a predetermined spark timing set for the engine speed and the engine load. For a second period following the first predetermined period, the spark control module: provides spark to a first one of the cylinders at a first spark timing that is retarded relative to the predetermined spark timing; and supplies spark to all of the other cylinders of the engine at the predetermined spark timing. The storage module selectively stores in memory: a first torque output of the engine measured during the first predetermined period; and a second torque output of the engine measured during the second period.

In one instance, disclosed herein is an engine system, comprising: an engine comprising a plurality of engine cylinders; and a controller operative to: control a respective ignition timing for each engine cylinder of the plurality of engine cylinders; detect an increase of a knock intensity of the engine; after detecting the increase of the knock intensity of the engine, compare the knock intensity of the engine to a threshold knock intensity; if the knock intensity of the engine is greater than the threshold knock intensity, retard the respective ignition timing for each engine cylinder of the plurality of engine cylinders by the same amount; and if the knock intensity of the engine is less than the threshold knock intensity, retard a first ignition timing of a first engine cylinder by a first amount independently of a second ignition timing of a second engine cylinder.