Abstract: A fuel control system that regulates a purge flow from a fueling system to an engine includes a sensor that monitors an engine speed and a first module that determines a PWM frequency of a purge valve based on the engine speed. The PWM frequency includes a first period that is based on a second period that corresponds to two engine cycles. A second module regulates the purge valve based on the PWM frequency during engine operation.

Abstract: A fuel control system that regulates a purge flow from a fueling system to an engine includes a sensor that monitors an engine speed and a first module that determines a PWM frequency of a purge valve based on the engine speed. The PWM frequency includes a first period that is based on a second period that corresponds to two engine cycles. A second module regulates the purge valve based on the PWM frequency during engine operation.

Abstract: A leak detection system for a vehicle includes a fuel system and a controller. The controller communicates with the fuel system to detect a fuel filling event. The controller initiates a vapor leak test of the fuel system and terminates the vapor leak test if a fuel filling event is detected.

Abstract: A fuel system with a pressure-sensitive monitor accumulates multiple pressure-related sample points and estimates the general trend of pressure change in a fuel system over time, thereby detecting the presence or absence of a fuel vapor leak in the fuel system.

Abstract: An idle air control system diagnostic for an internal combustion engine which utilizes RPM, engine timing and intake airflow measurements to detect the presence of idle RPM faults and eliminate or verify the idle air control system as the fault source. Engine idle RPM is measured and compared with a commanded idle RPM, and if within a predetermined range, an idle RPM fault exists and one of two additional tests (non-intrusive and intrusive) is conducted to determine whether the idle air control system is the source of the fault. In the non-intrusive test, intake airflow is measured and compared to a predetermined intake airflow value, and if not within a predetermined range, the idle air control system is determined to be the fault source. In the intrusive test, variations in intake airflow (or intake manifold pressure) are measured in response to variations in the movement of the engine throttle-bypass airway pintle.

Abstract: A comprehensive air injection system diagnostic uses hardware already available on many vehicle exhaust systems to monitor the oxygen content of the exhaust, so as to indicate steady state oxygen levels therein that are not in accord with the present state of the air injection system, and accordingly are assumed to be the result of a failure in the air injection system.