Gasoline reid vapor pressure (RVP), the vapor pressure of gasoline measured at 100.degree. Fahrenheit under specified measurement procedures, is generally recognized as a measure of fuel volatility. High gasoline RVP improves engine startability and driveability at low ambient temperature, but can have a negative effect on the precision of certain fueling system diagnostics. RVP can vary significantly between available fuels. It would be desirable, for a given fuel, to determine its RVP and to adjust fueling system control and diagnostics in response to the determined RVP for improved performance and for increased diagnostic integrity.
Conventional RVP measurement is conducted through analysis of a sample of fuel under laboratory conditions. The measurement results are not currently applied in control and diagnostics procedures on-board automotive vehicles. On-board re-fueling vapor recovery (ORVR) systems (also referred to herein as fuel vapor recovery systems) have been proposed for application on-board automotive vehicles. ORVR systems include a canister with fuel vapor adsorbing material through which re-fueling vapors are passed and in which such vapors are trapped during re-fueling procedures for controlling evaporative fuel vapor emissions. The trapped ORVR vapors are, from time to time during engine operation, purged from the adsorbing material for consumption in the engine. The rate of purge of the ORVR vapors has been determined to vary with fuel RVP. It would be therefore be desirable to estimate RVP using such purge rate information from ORVR systems.