Monitoring apparatus for fuel feed system

A monitoring apparatus for monitoring a fuel feed system of an internal combustion engine, comprising an electronic control unit and an air fuel ratio detector provided in an exhaust system of the engine, said electronic control unit being programmed to:

• perform feedback control of the A/F ratio based on an output of the detector;
• calculate an A/F ratio feedback coefficient according to the output of the detector;
• calculate a malfunction determination parameter based on the A/F ratio feedback coefficient;
• suspend purging when the parameter reaches a first decision value;
• suspend monitoring when the parameter reaches a second decision value in a purge cut state;
• and to estimate, responsive to the malfunction determination parameter reaching the second decision value, a value of the malfunction determination parameter it would take if purge cut was not carried out, an initial value of the estimation being the value when the parameter reached the first decision value.

A Method for monitoring a fuel feed system of an internal combustion engine having an electronic control unit and an air fuel ratio detector provided in an exhaust system of the engine comprising:

• performing feedback control of the A/F ratio based on an output of the detector;
• calculating an A/F ratio feedback coefficient according to the output of the detector;
• calculating a malfunctioning determination parameter based on the A/F ratio feedback coefficient;
• suspending purging when the parameter reaches a first decision value;
• suspending monitoring when the parameter reaches a second decision value in a purge cut state;
• and
• estimating, responsive to the malfunction determination parameter reaching the second decision value, a value of the malfunction determination parameter it would take if the purge cut was not carried out, an initial value of the estimation being the value when the parameter reached the first decision value.