Most industrial and automotive internal combustion engines include a pair of cylinder banks, each including a plurality of cylinders. For example, a V-8 engine includes two banks of four cylinders each. With the advent of electronic controls, the operating conditions of each of the cylinders is controlled by an on-board engine control computer or an electronic controller. The typical electronic controller provides signals to electrically actuated fuel control systems, firing timing systems and air intake systems. In diesel engines, the electronic controller performs the critical task of controlling the timing of operation of the fuel injectors to ensure optimum combustion performance. The electronic controller also acts as a speed governor, accepting input from the accelerator pedal and sensing engine load conditions to establish an engine speed.
Power imbalance between engine cylinders can have obviously deleterious effects on overall engine performance. Moreover, cylinder power imbalance can cause an engine to "run dirty" so that the engine emissions exceed federal and local environmental regulations. The causes of cylinder power imbalance are many, but can be broadly categorized as reductions in combustion quality. This reduction can arise in a diesel engine from a drop in injector nozzle opening pressure, a stuck plunger, clogged injectors, unsealed valves, valve gap discrepancies, and the like. Other causes can arise in the fuel pump or can be attributed to a "dead" cylinder.
Many approaches have been implemented to identify when a cylinder power imbalance exists, or when a particular cylinder performance is below acceptable operating limits. However, these prior approaches only operate as a sort of "go-no go" gauge and are generally only useful to determine that a cylinder is a problem. Thus far, none of these prior systems can diagnose the source of the engine power problem. Moreover, no prior system has the capability to provide a prognosis of future engine performance so that the vehicle operator can avoid break-downs on the road due to deteriorating engine performance.
Consequently, there remains a need in the arena of engine performance evaluation for a system that can not only diagnose, but also predict engine performance problems. This need is best fulfilled by an on-board system that performs its appointed evaluation automatically when the engine is at idle conditions.