Fault diagnostic for an internal combustion engine having air assisted injectors

A method of diagnosing faults in an air assisted fuel injector system including an air assisted fuel injection for an internal combustion engine having electronic throttle control comprising:

• determining a first expected airflow value indicative of the expected airflow entering an intake of the electronic throttle of the engine to maintain engine idle speed with the air assisted injector system operating at a first rate of airflow;
• determining a second expected airflow value indicative of the expected airflow entering the air assisted injector system of the engine to maintain engine idle speed with the air assisted injector system operating at said first rate of airflow;
• generating a first value indicative of the airflow entering an intake of the electronic throttle of the engine at idle speed with the air assisted injector system operating at said first rate of airflow;
• determining a first error signal equal to the difference between said first value and the first expected airflow value;
• operating the air assisted injector system at a second rate of airflow corresponding to the air assisted fuel injector being off;
• generating a second value indicative of the actual airflow entering the intake of the electronic throttle of the engine at idle speed with the air assisted injector system operating at said second rate of airflow;
• determining a second error signal equal to the difference between said second value and the sum of the first and second expected airflow values;
• and
• generating a fault signal as a function of said first and second error signals.