Diagnosis for fuel system of internal combustion engine

A diagnostic control system for detecting malfunction in a fuel system for a fuel injection type internal combustion engine, comprising:

• a fuel pressure sensor for sensing an actual fuel pressure for the engine;
• a pressure controlling section for performing a feedback fuel pressure control to reduce a pressure deviation of the actual fuel pressure sensed by the fuel pressure sensor from a desired fuel pressure;
• an abnormality detecting section for detecting abnormality in the fuel system by monitoring the actual fuel pressure;
• a richer combustion mode effecting section for effecting a feedback air fuel ratio control in a predetermined richer combustion mode if the abnormality is detected;
• and
• a diagnosing section of judging whether the abnormality is attributable to the fuel pressure sensor, by monitoring performance of the feedback air fuel control in the richer combustion mode.

An engine system comprising:

• an internal combustion engine;
• a fuel system comprising a fuel injector for supplying fuel to the engine, and a fuel pump for supplying the fuel under pressure to the fuel injector through a fuel delivery circuit;
• a first input device for producing a first input signal representing a sensed actual fuel pressure in the fuel delivery circuit;
• and
• a controller for performing a feedback fuel pressure control to reduce a pressure deviation of the sensed actual fuel pressure from a desired target fuel pressure (tFP), for detecting abnormality in the fuel system by monitoring the pressure deviation, for commanding a changeover of combustion in the engine from a lean combustion mode to a richer combustion mode to effect a feedback air fuel ratio control if the abnormality is detected, and for judging whether the abnormality is attributable to the fuel pressure sensor, by monitoring a feedback correction quantity of the feedback air fuel control in the richer or combustion mode.