Systems and methods for onboard canister purge valve flow mapping

A system for a hybrid vehicle, comprising:

• a fuel vapor storage canister positioned in an evaporative emissions system;
• a canister purge valve positioned in a purge line fluidically coupling the fuel vapor storage canister to an intake of an engine;
• a pump positioned in a vent line that couples the fuel vapor storage canister to atmosphere, the pump including a changeover valve configurable to a first position and a second position where the vent line is sealed from atmosphere when the changeover valve is configured in the second position, the pump further including a reference orifice and a pressure sensor configured to measure a pressure difference across the reference orifice;
• a vacuum source downstream of the fuel vapor storage canister for applying a predetermined negative pressure on the evaporative emissions system;
• and
• a controller with computer readable instructions stored on non-transitory memory that, when executed, cause the controller to:
• obtain a first baseline rate and a second baseline rate at which pressure in the evaporative emissions system is reduced to a predetermined vacuum level by configuring the changeover valve in the second position to seal the evaporative emissions system and applying the predetermined negative pressure on the evaporative emissions system via the vacuum source while the canister purge valve is duty cycled at a first rate and then a second rate;
• at a later time, obtain a first test rate and a second test rate at which pressure in the evaporative emissions system is reduced to the predetermined vacuum level by configuring the changeover valve in the second position and applying the negative pressure on the evaporative emissions system via the vacuum source while the canister purge valve is duty cycled at the first rate and then the second rate;
• compare the first and second test rates with the first and second baseline rates to obtain a degradation factor that is used to update a flow map stored at the controller that is used to control the canister purge valve for purging fuel vapors from the fuel vapor storage canister;
• and
• in response to a request to purge the fuel vapor storage canister, controller the canister purge valve based on the updated flow map.