Abstract: An ionization current sensing circuit providing a way to detect the combustion event in a spark ignited engine cylinder. The presence of an output signal from the proposed circuit indicates that a flame exists and that combustion has occurred in the cylinder. This signal is drastically changed if combustion is absent, the circuit providing viable engine misfire detection. The ionization current sensing circuit comprising a power source for providing voltage directly to the primary winding of the ignition coil, an integrator for integrating a spark plug ionization current and thereby providing a voltage output in proportion to the integral of the ionization current, and an ionization current sensing module for sensing a spark plug ionization current, the ionization means connected between the secondary winding of the ignition coil and the integrator means.