We report a low-cost fiber-optic combustion pressure sensor integrated with an ignition system of a passenger car. A miniature sensor is attached to a shaft extending from the spark plug boot. Simultaneously with the boot mounting on the spark plug the sensor shaft is pressed into a cylindrical hole of a modified production spark plug. The sensor cable is combined either with the boot, or boot and high voltage cable, depending whether a coil-at-plug or a Distributed Ignition System is used, respectively. The sensor optical and Application Specific Integrated Circuit (ASIC) components are packaged inside a miniature module, embedded either in a coil-at-plug package or a Distribute Ignition System module. Engine test results are reported for a single-cylinder, gasoline fueled stationary gen-set engine. When optimized for high linearity and reduced thermal shock, the spark plug-mounted sensor demonstrates approximately +/-1.5% pressure reading accuracy, comparable to that of a laboratory-grade piezoelectric transducer. With the life-time of 200 Million pressure cycles and targeted price of $7 to $10, the sensor meets the performance, durability, and cost requirements for production car applications.