Abstract: Sensor apparatus for a multiple layer steel (MLS) cylinder head gasket measures combustion pressures for detecting engine conditions. A membrane is positioned at one end of an elongated metal tube, and the membrane end of the tube engages a cylinder bore boundary. A fiber optical sensor apparatus is fixed within the tube, and communicates with cyclic combustion events via the membrane. In one disclosed embodiment, optical wires from sensor apparatus situated at each engine bore are bundled into a common groove machined into an extended spacer layer radially outwardly of the conventional boundary of the gasket. The tube protects the sensor apparatus from damage of sealing stress on the gasket, and particularly at the bore perimeter. Each tube lies in a separate groove in the spacer layer that terminates at the bore boundary. A converter changes optical signals received from the apparatus into electrical signals for transmittal to a controller.