EVAP System: Description: Notes
While the engine is running, if a predetermined condition (closed loop, etc.) is met, the EVAP 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 EVAP 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.
COMPONENTS OPERATION CHART
| Components | 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. |
| EVAP VSV | Opens or closes line between canister and intake manifold. ECM opens and closes EVAP 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. |
| Service port | Used for connecting vacuum gauge for inspecting EVAP system. |
| Soak timer | Built into ECM. To ensure that EVAP monitor values will be accurate, soak timer counts 5 hours (-15 minutes) from when ignition switch is turned off. This will allow fuel to cool down, which will stabilize Fuel Tank Pressure (FTP). When approximately 5 hours have passed, ECM turns ON (refer to Fig 5). |
| Fuel vapor-containment valve | 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) |
| Pump module | (a) to (e) below are pump module components. 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 EVAP VSV, turning on vent valve (closed) and operating vacuum pump (refer to Fig 3). |
| (b) 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) Vacuum pump | Negative pressure (vacuum) is created in EVAP system for leak check. |
| (e) 0.02 inch orifice | Diameter is 0.02 inch. Negative pressure (vacuum) is created in 0.02 inch orifice to measure "0.02 inch leak pressure" by closing EVAP VSV, turning off vent valve (vent) and operating vacuum pump. "0.02 inch leak pressure" indicates criterion of EVAP small leak. |