Abstract: Disclosed is a transducer assembly and diagnostic apparatus for processing an electrical signal which varies with the pressure changes occurring within an engine cylinder. The transducer assembly consists of a U-shaped structure integrally formed in a sandwich arrangement and encompassing a pressure-responsive crystalline element. The assembly is sized such that it substantially encompasses the shank of a spark or glow plug of the engine such that axial forces from within the cylinder excite the transducer through the plug to produce a signal which is processed in an electrical circuit to provide timing or other diagnostic information.

Abstract: A transducer and associated diagnostic system for fuel injected diesel engines of the type having glow plugs to provide supplementary ignition during starting and warm-up periods. A piezoelectric transducer unit is adapted to screw into the receptacle normally provided in each cylinder for a glow plug. The unit includes a piezoelectric element which is held under tension by a conductive rubber plug which coacts with a coaxial connector in transmitting the pressure indicative output signal. The transducer develops an electrical signal which varies in accordance with the pressure-time characteristic of the cylinder combustion chamber, the electrical signal representing performance of each cylinder being processed individually to provide timing and other valuable information or being combined with electrical signals developed for other cylinders of the engine in a comparative diagnostic system.