Leak Detection Pump

Immediately after a cold start, when engine temperature is between 40°F and 86°F, 3-port solenoid is briefly energized. This initializes pump by drawing air into pump cavity and also closes vent seal. During non-test test conditions, vent seal is held open by pump diaphragm assembly which pushes it open at full travel position. The vent seal will remain closed while pump is cycling. This is due to operation of 3-port solenoid which prevents diaphragm assembly from reaching full travel which would dumps pump pressure to atmosphere. After brief initialization period, solenoid is de-energized, allowing atmospheric pressure to enter pump cavity. This permits spring to drive diaphragm which forces air out of pump cavity and into vent system. When solenoid is energized and de-energized, cycle is repeated creating flow in typical diaphragm pump fashion. The pump is controlled in 2 modes:

PUMP MODE:  The pump is cycled at a fixed rate to achieve a rapid pressure build in order to shorten overall test time.

TEST MODE:  The solenoid is energized with a fixed duration pulse. Subsequent fixed pulses occur when diaphragm reaches switch closure point.

The spring in pump is set so that system will achieve an equalized pressure of about 7.5" of water. When pump starts, cycle rate is quite high. As system becomes pressurized, pump rate drops. If there is no leak, pump will quit. If there is a leak, test is terminated at end of test mode.

If there is no leak, purge monitor is run. If cycle rate increases due to flow through purge system, test is passed and diagnostic is complete. The canister vent valve will unseal system after completion of test sequence as pump diaphragm assembly moves to full travel position.