ENGINE MONITORING SYSTEM

A system for monitoring the performance of an internal combustion engine includes a pressure sensor that has a mounting configuration external to cylinders such that it is capable of monitoring the pressures within two adjacent cylinders. The signal output of the sensor is filtered to remove undesired engine noise and blank out those signals which are unrelated to compression and firing, thereby reducing errors in the signal output. After filtering the signals to reduce noise,a successive number of samples related to compression and firing are obtained to provide an adequate number of signals which will average out mechnical and electrical noise. From the successive samples, a straight line approximation of the slope of the cylinder pressure curve, relative to crank angle, is obtained. The derived slope values are compared with upper and lower limits to determine whether or not the pressure within the engine cylinder of interest is acceptable. If the upper limit is exceeded or if the value obtained is less than the lower limit a fault in the cylinder operation is assumed to have occurred. This fault measurement and analysis procedure is repeated a prescribed number of times and if the problem continues to occur over a predetermined consecutive number of measurements, then a fault indication is generated.