A modified pressure sensor mounted in the engine exhaust manifold to measure pressure fluctuations has been developed by Kavlico Corp. The misfire detection system is capable of sensing a spark ignition misfire at all load conditions from idle speed to 6000 rpm on engine configurations up to eight cylinders and on V12 engines by monitoring each exhaust manifold separately. When installed on spark ignition engine exhaust systems between the engine and catalytic converter, the system has the capability of detecting increasing resistance to flow through the catalytic converter, to initiate warning to the engine operator. The sensor is used in conjunction with Kavlico's decision logic circuit which is based on the use of a Motorola MC68HC11 microcontroller.