Abstract: An engine diagnostic apparatus includes a first transducer positioned in the oil filler neck of the engine for translating the crankcase pressure waveform into a corresponding electrical waveform having a frequency component proportional to engine speed. A second transducer is positioned to translate an exhaust pressure waveform emitted by the engine to a corresponding electrical waveform having a frequency component representative of an engine fault at a frequency proportional to engine speed. The two frequency components are compared to provide diagnostic information.

Abstract: The cylinder of an internal combustion engine having a fault is identified by using a non-contacting transducer to generate a reference engine-cycle electrical signal having a phase determined by a reference one of the cylinders of the engine, and by using a non-contacting transducer to generate a fault engine-cycle electrical signal having a phase determined by the one of the cylinders having a fault. The phase difference between the fault electrical signal and the reference electrical signal is translated to a number identifying the cylinder having the fault.

Abstract: A conduit arrangement for measuring unburned combustibles in the exhaust eam issuing from an engine. A restriction is provided in the exhaust duct to form a superatmospheric pressure zone upstream from the restriction and a subatmospheric pressure zone downstream from the restriction. A minor fraction of the exhaust gas is bypassed around the restriction through a conduit system communicating with the two above-mentioned zones. A sampling chamber containing a combustibles sensor is located in the conduit system. An auxiliary conduit communicates the interior of the sampling chamber with the ambient atmosphere so that cooling air is drawn into the chamber to dilute the sampled gas. The dilution air lowers the temperature of the gas-air mixture, thereby cooling the sensor against heat degradation by the otherwise undiluted gas. The dilution air also contributes oxygen to the gas stream, thereby enhancing catalytic oxidation processes on which certain sensors depend for response to combustibles (CO and CH).