<div class="htmlview paragraph">Over the last two decades, advanced engine control systems have been developed that use cylinder pressure as the primary feedback variable. Production application has been limited by cost, reliability, and packaging difficulties associated with intrusive cylinder pressure sensors. Now, a low-cost cylinder-pressure-based engine control system has been developed that utilizes Pressure-Ratio Management (PRM) and non-intrusive cylinder pressure sensors mounted in the spark plug boss of four-valve-per-cylinder engines. The system adaptively optimizes individual-cylinder spark timing and air-fuel ratio, and overall exhaust gas recirculation (EGR) for best fuel economy and lowest emissions over the life of each vehicle.</div> <div class="htmlview paragraph">This paper presents the engine control and cylinder pressure sensor systems. Results are presented showing spark timing and EGR control, knock and misfire detection, cylinder-to-cylinder air/fuel balancing, and cold start control.</div>