EVAP System: Description: Notes
While the engine is running, if a predetermined condition (closed loop, etc.) is met, the purge VSV is opened by the ECM and stored fuel vapors in the canister are purged to the intake manifold. The ECM will change the duty cycle ratio of the purge VSV to control purge flow volume.
Purge flow volume is also determined by the intake manifold pressure. Atmospheric pressure is allowed into the canister through the vent valve to ensure that purge flow is maintained when negative pressure (vacuum) is applied to the canister.
The ECM monitors the condition of both the key-off monitor and purge flow monitor to ensure proper operation of the EVAP system.
EVAP SYSTEM COMPONENTS OPERATION CHART
| Component | Operation |
|---|---|
| Canister | Contains activated charcoal to absorb EVAP that is created in fuel tank. |
| Cut-off valve | Located in the fuel tank. Valve closes by its own weight when vehicle is overturned to prevent fuel from spilling out. |
| Purge VSV | Opens or closes line between canister and intake manifold. ECM opens and closes purge VSV to control EVAP purge flow. ECM opens purge valve to purge vapor gas that was absorbed by canister to intake manifold. ECM controls EVAP volume purged to intake manifold by duty cycle (current-carrying time) to purge valve. (ON: Open, OFF: Closed) |
| Roll-over valve | Located in fuel tank. Valve floats and closes when fuel tank is filled to 100%. Also, valve close by its own weight when vehicle is over turned to prevent fuel from spilling out. |
| Soak timer | Built into ECM. Soak timer counts power switch OFF time. |
| Fuel vapor-containment valve (FVCV) | Opens and closes line between fuel tank and canister. When vehicle is stopped, this valve closes to keep vapor in the tank and prevent it from being absorbed in canister. During refueling, valve opens and vapor is absorbed in canister. When driving, valve acts to change pressure in the tank slightly positive. |
| Fuel tank pressure sensor | Converts fuel tank pressure into voltage and outputs that voltage. ECM supplies a constant voltage of 5 V to pressure sensor and uses feedback from sensor to monitor fuel tank pressure, (Fig 5) |
| Canister pump module | (a) to (e) below are canister pump module components. Canister pump module cannot be disassembled. |
| (a) Vent valve | Vents and closes EVAP system. When ECM turns valve ON, EVAP system is closed. When, ECM turns valve OFF, EVAP system is vented. Negative pressure (vacuum) created in EVAP system to check EVAP leaks by closing purge VSV, turning on vent valve (closed) and operating vacuum pump (refer to Fig 3). |
| (b) Canister pressure sensor | Indicates EVAP pressure as voltage 5 V is applied by ECM. ECM detects EVAP system pressure using this voltage (refer to Fig 4). |
| (c) Check valve | Composed of nylon ball and spring. Valve blocks off atmosphere from the vacuum pump. |
| (d) Leak detection pump | Negative pressure (vacuum) is created in EVAP system for leak check. |
| (e) Reference orifice | Diameter is 0.02 inch. Negative pressure (vacuum) is created in reference orifice to measure reference pressure by closing purge VSV, turning off vent valve (vent) and operating leak detection pump. Reference pressure indicates criterion of EVAP small leak. |