Abstract: A method of leak detection for an evaporative emission control system during periods of low engine vacuum includes the steps of pulsing a leak detection pump at a predetermined rate and determining whether engine vacuum level is low. The method also includes the steps of maintaining pressurization of the evaporative emission control system if the engine vacuum level is low, maintaining pressurization behind a vapor canister vent valve if the engine vacuum level is low, and detecting for leaks in the evaporative emission control system after a normal engine vacuum level is attained.

Abstract: A system and method of monitoring the purge flow in an evaporative emission control purge system of a motor vehicle. Signals indicative of engine speed, fuel control and automatic idle speed position are measured and used to determine whether the purge flow system is operating properly. With purge flow activated, the amount of purge flow is increased in accordance with a ramping rate and the measured signals are monitored to determine whether or not a change occurs in any one of the engine speed, fuel control and AIS position signals.

Abstract: A method of leak detection for an evaporative emission control system to determine if a leak is present in a portion of the system includes the steps of energizing a leak detection pump to close a canister vent control valve of the system and pressurize the system, and determining whether a possible pinched line of the system has occurred.

Abstract: A method of testing an evaporative emission control system to determine if the evaporative emission control system has reached a predetermined pressure includes the steps of pulsing a leak detection pump at a predetermined rate and determining if a last pump period is greater than or equal to a predetermined test mode period threshold. The method also includes the steps of pressurizing the evaporative emission control system if the last pump period is less than a test mode period threshold and continuing the method if the last pump period is equal to or greater than the test mode period threshold.

Abstract: A flexible fuel compensation system including a method of methanol boil-off compensation. The methanol boil-off compensation method includes an initialization routine, a run mode routine and a shutdown routine. The method will monitor a plurality of flags to determine when the methanol boil-off compensation should be used.

Abstract: A flexible fuel compensation system including a method of start fuel decay. The start fuel decay method interpolates decay rates based on the coolant temperature. The decay rate is then subtracted from the decayed start fuel pulsewidth until it reaches a predetermined value.

Abstract: A flexible fuel vehicle is a vehicle capable of operating on alcohol, gasoline, or any combination of these two fuels. Because of the unique properties of alcohol fuels, modifications to engine operating characteristics are required to compensate for the varying percentage of alcohol in the fuel. A method is provided for determining the percent alcohol content of the fuel in the fuel tank, utilizing the oxygen sensor feedback control loop to sense changes in air/fuel ratio and relay that information to the engine controller so that dependant variables can be adjusted accordingly. The method includes placing the fuel pump in the fuel tank along with a mixed fuel accumulator so that a known and slowly varying percentage of alcohol in the fuel is provided to the engine, especially during open loop operation.