Detecting malfunction in cylinders of internal combustion engines

The method of detecting malfunctioning in individual cylinders of an internal combustion engine, comprising the steps of:

• measuring the engine power time periods between crankshaft positions representing successive ignition times in successively fired cylinders of the engine,
• subtracting each measured time period from the following measured time period to determine individual deceleration rates between successive time periods,
• computing the average deceleration rate for each cylinder, and
• comparing each individual deceleration rate with the average deceleration rate for the corresponding cylinder, and registering a misfire when the individual deceleration rate exceeds the average by more than a predetermined limit value.

Apparatus to detect malfunctioning in individual cylinders of an internal combustion engine, comprising:

• means for measuring the engine power time periods between crankshaft positions representing successive ignition times in successively fired cylinders of the engine,
• means for subtracting each measured time interval from the following measured time period to detect whether there is a positive difference representing a momentary reduction in engine speed,
• comparator means producing a fault output whenever a time difference exceeds a predetermined limit value, to provide an indication of a significant fault in an individual cylinder,
• means for counting the number of faults occurring during a predetermined period, and
• comparator means for determining whether the number of faults exceeds a predetermined limit value above which engine performance is considered unsatisfactory.