Abstract In this paper, a spark advance self-optimization strategy is presented for lean-burn operation mode of spark-ignition (SI) engine which aims on-board combustion phase tuning to achieve high efficiency under a probability constraint of knocking events. Firstly, the effects of spark advance (SA) on combustion phase under lean-condition are analyzed in a statistical perspective based on experiments. Then, based on conclusion of the analysis, a SA control scheme, which combines extremum seeking loop with likelihood-based knock limit control loop, is proposed to optimize SA for maximal fuel economy with knock probability threshold. Finally, experimental validation results are demonstrated that are conducted on a test bench with a V6 commercial SI engine.