Relative manifold vacuum of an internal combustion engine

Apparatus for measuring the relative manifold vacuum contribution between cylinders of an internal combustion (IC) engine connected through its crankshaft to the drive shaft of an engine load and running at a selected speed, comprising:

• position sensing means, adapted to be disposed along the drive shaft for providing crankshaft position signals indicative of the instantaneous angular position of the engine crankshaft at successive angle intervals within the engine cycle, each angle interval being less than that associated with a cylinder sub-cycle;
• manifold vacuum sensing means, adapted to be disposed on the engine for providing signals indicative of the actual engine manifold vacuum;
• and
• signal processing means, responsive to said crankshaft position signals and said actual engine manifold vacuum signals and having memory means for storing signals including signals definitive of the engine cycle,
• for sampling and storing in said memory means, successive values of said actual manifold vacuum signals in response to the presense of each of said crankshaft position signals, to provide an indication of the sub-cyclic fluctuations in manifold vacuum over at least one engine cycle, and
• for comparing the magnitudes of each of said sub-cyclic fluctuations occurring in a common engine cycle with each other to provide signal indications of the relative manifold vacuum contribution between cylinders.