Abstract: An on-board diagnostic system for performing a diagnostic test on a fuel delivery system. The diagnostic system is controlled by a controller such as a powertrain control module or an electronic engine controller. With the engine off and key on, fuel is delivered to the engine's fuel rail. A standard, production pressure sensor in fluid communication with the fuel rail records the pressure in the fuel delivery system. The recorded pressure is then compared to a stored acceptable pressure range to determine whether the fuel delivery control means is delivering fuel to the fuel rail and whether the fuel delivery system is holding pressure. Each fuel injector is then actuated for a specified time. When the injector is actuated, the fuel pressure drop sensed by the pressure sensor is compared to a stored pressure drop range to determine whether the injector is faulty.

Abstract: An engine controller compensates for changes in air pressure and intake of the engine during engine crank which are caused by injection of fuel into the intake. The engine controller compares rotational speed of the engine to a threshold value and determines a cylinder air charge value in a first manner if the engine speed is greater than or equal to the threshold value. If the engine speed is less than the threshold value then the reliability of an air meter positioned in the intake is tested and if the air meter is determined to be of sufficient reliability then the cylinder air charge is determined in a second manner. If the air meter is determined to be unreliable then the operability of a throttle position sensor is determined and if the throttle position sensor is determined to be operable then the cylinder air charge is determined in a third manner.