Methods and systems are provided for diagnosing a vehicle fuel system for a presence or absence of undesired evaporative emissions. In one example, a method comprises evacuating the fuel system of a vehicle to a variable vacuum target as a function of a volatility of fuel in a fuel tank positioned in the fuel system and a loading state of a fuel vapor storage canister configured for capturing and storing fuel vapors from the fuel tank. In this way, analysis of a pressure-bleedup portion of the diagnostic may be more reliable and completion rates of the diagnostic may be improved, while conducting the test in an environmentally fashion.

A method of determining fuel leak of fuel injectors of an injection system of a combustion engine, said method including determining a baseline pressure based on a predetermined integral response threshold and for each fuel injector determining a primary reference integral response by obtaining the associated primary reference integral response by obtaining the current integral response while running the engine at the baseline pressure with the respective fuel injector fluidly isolated.

A first pressure sensor is disposed in a first fuel system between a first shutoff valve and a second shutoff valve. A second pressure sensor is disposed in a second fuel system between the second shutoff valve and a fuel injection valve. A determination process determines a leakage anomaly in the first fuel system or the second fuel system based on a first magnitude relationship or a second magnitude relationship. The first magnitude relationship is a relationship between a detection value of the first pressure sensor in a state in which the first fuel system is filled with gaseous fuel and a first threshold value. The second magnitude relationship is a relationship between a detection value of the second pressure sensor in a state in which the second fuel system is filled with gaseous fuel and a second threshold value.

Systems and methods utilize a controller configured to perform a diagnostic routine for a combustion seal provided between a gasoline direct injection (GDI) fuel injector and a combustion chamber of a cylinder of a GDI engine. The diagnostic routine comprises determining one of (i) a period for the injector coil current to reach a peak current and (ii) a resistance of the injector coil while the injector coil current is saturated, determining whether the determined period or the determined injector coil resistance is greater than a respective threshold indicative of a predetermined temperature of the injector coil, and when the determined period or the determined injector coil resistance is greater than its respective threshold, detecting a combustion seal leak fault. Based on the combustion seal leak fault, the controller may modify operation of the engine to prevent potential heat damage to the engine.

After an engine is started, pump monitoring is performed as follows: a canister is opened to the atmosphere; a negative pressure pump is activated; and abnormality of the negative pressure pump is evaluated on the basis of canister pressure Pc detected with a pressure sensor in an evaporative leakage check module, and after the pump monitoring is completed, a switching valve is closed so that the negative pressure pump communicates with the canister for purge any fuel evaporative gas into an intake passage of the engine, and whether or not leakage has occurred in a fuel evaporative gas emission suppressor is evaluated based on the canister pressure Pc.

A method of determining fuel leak of fuel injectors of an injection system of a combustion engine, said method including determining a baseline pressure based on a predetermined integral response threshold and for each fuel injector determining a primary reference integral response by obtaining the associated primary reference integral response by obtaining the current integral response while running the engine at the baseline pressure with the respective fuel injector fluidly isolated.

A method for detecting defective injection nozzles that deliver fuel into the combustion chambers of an internal combustion engine includes determining the standard deviation values for the respective injection nozzles and of the total leakage flow via a computation. The computation involves solving an equation for a respective test step that describes the standard deviation values and the total leakage flow as a function of the mixture factors set in a respective test step, a lambda value that is valid for a respective test step and that is derived from the measurements of the lambda value, and an air mass flow that is valid for the respective test step and that is derived from the measurements of the air mass flow.

Various systems are provided for delivering fuel to an engine. In one example, a system includes a controller and a fluid system configured to maintain a fluid at a pressure downstream of a check valve. The controller may be configured to determine if a leak is present in the fluid system based on a first pressure decay rate of the fluid system, and responsive to identifying that a leak is present in the fluid system, differentiate between an internal leak and an external leak based on a leak flow rate as fluid system pressure decreases.

A failure detection apparatus for fuel systems of an engine includes a first failure determiner executing, while the engine is in each of a first injection form and a second injection form, a failure determination process on the corresponding fuel system, a second failure determiner executing, when the first failure determiner determines occurrence of a failure in one of the injection forms, a failure determination process on the fuel system corresponding to the other injection form, a failure locator determining whether or not the failure has occurred, for each of the fuel systems responsible for the first and second injection forms, based on a result by the second failure determiner, and a purge process prohibiter prohibiting execution of a purge process for the engine. The second failure determiner causes the purge process prohibiter to prohibit execution of the purge process, when executing the failure determination process on the fuel system.

A method of diagnosing a high pressure fuel delivery system includes sensing an after shutdown fuel pressure in the fuel rail. An after shutdown leak rate is calculated from the after shutdown fuel pressure, and compared to a shutdown leak threshold. The high pressure fuel delivery system is analyzed to detect a leak in one of the fuel rail or the fuel injector when the after shutdown leak rate is greater than the shutdown leak threshold. A cranking fuel pressure in the fuel rail is also sensed. A cranking leak rate is calculated from the cranking fuel pressure, and compared to a cranking leak threshold. The high pressure fuel delivery system is analyzed to detect a leak in the high pressure fuel pump when the cranking leak rate is greater than the cranking leak threshold.