Abstract: A method of monitoring air flow restriction in an air intake of an internal combustion engine includes recording a predetermined number of pre-throttle pressure samples, recording a predetermined number of mass air flow samples, which respectively correspond to the pre-throttle pressure samples and determining a slope based on the pre-throttle pressure samples and the mass air flow samples. Whether an air filter is inducing an air flow over restriction is determined based on the slope.

Abstract: A method of monitoring air flow restriction in an air intake of an internal combustion engine includes monitoring a plurality of manifold absolute pressure (MAP) samples and determining respective MAP thresholds corresponding to each of the MAP samples. Each of the MAP samples is compared to its respective MAP threshold. A percentage of failed MAP samples is determined based on the comparing and an over-restricted air intake condition is selectively indicated based on the percentage of failed MAP samples.

Abstract: An engine idle fault control system that identifies a source of rough idle in an engine includes a first module that monitors an idle speed of the engine and that generates a rough idle signal, and a second module that monitors a fuel control parameter. A third module determines a source of rough idle based on the fuel control parameter and the rough idle signal.

Abstract: A diagnostic control system for a purge valve that regulates fuel vapor flow from a fuel system into an intake manifold for an engine includes a calculation module and a malfunction module. The calculation module estimates a plurality of areas based on a plurality of pressure signals and calculates an average rate of increase of vacuum pressure in the fuel system during operation of the purge valve. The malfunction module determines whether the average rate of increase of vacuum pressure is within a predetermined range generating a purge valve functioning signal, and generates a purge valve malfunction signal when the average rate of increase of vacuum pressure is not within the predetermined range.

Abstract: A liquid fuel detection system for a fuel vapor system of a vehicle providing fuel vapor to an engine operating in closed loop includes an oxygen sensor that generates an oxygen signal based on an oxygen level in engine exhaust. An engine speed sensor generates a speed signal based on a speed of the engine. And a control module receives the oxygen signal and the speed signal, determines a fuel control factor based on the oxygen signal, determines a long term modifier based on long term changes of the fuel control factor, and detects the presence of liquid fuel in the fuel vapor system based on the fuel control factor, the speed signal, and the long term modifier.

Abstract: A method of diagnosing a malfunction of a tuning valve of an intake manifold coupled to an internal combustion engine is provided. The method includes: commanding the tuning valve to at least one of a closed and an opened position; computing an average deviation of manifold absolute pressure; determining an average deviation threshold using fuzzy logic based on engine speed and airflow per cylinder; comparing the average deviation to the average deviation threshold; and diagnosing a malfunction of the tuning valve based on a comparison of the average deviation and the average deviation threshold.

Abstract: A leak detection system for a vehicle fuel tank includes a sensor that is responsive to a pressure within the fuel tank and that generates a pressure signal based thereon. A control module initiates an engine-off natural vacuum (EONV) test and determines a pressure change based on the pressure signal. The control module pauses the EONV test when the pressure change exceeds a pressure change threshold.

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: 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.