EVAP System Operation
The evaporative emission (EVAP) control system limits fuel vapors from escaping
into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due
to pressure in the tank, through the vapor pipe into the EVAP canister. Carbon in
the canister absorbs and stores the fuel vapors. Excess pressure is vented through
the vent line to the atmosphere. The EVAP canister stores the fuel vapors until the
engine is able to use them. At an appropriate time, the control module will command
the EVAP purge valve ON open, allowing engine vacuum to be applied to the EVAP canister.
Fresh air will be drawn through the vent line to the EVAP canister. Fresh air is drawn
through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture
continues through the EVAP purge pipe and EVAP purge valve into the intake manifold
to be consumed during normal combustion.
EVAP System Components
The EVAP system consists of the following components.
EVAP Canister
The EVAP canister is a sealed unit with 3 ports.
The canister is filled with carbon pellets used to absorb and store fuel vapors.
Fuel vapor is stored in the canister until the control module determines that the
vapor can be consumed in the normal combustion process.
EVAP Purge Solenoid Valve
The EVAP purge valve controls the flow of vapors from the EVAP system to the
intake manifold. This normally closed valve is pulse width modulated by the control
module to precisely control the flow of fuel vapor to the engine. The valve will also
be opened during some portions of the EVAP testing, allowing engine vacuum to enter
the EVAP system.
Evaporative Emission System Tester
TheJ 41413-200
Evaporative Emission
System Tester is used to help locate leaks in the EVAP system. The EEST provides a
clean, dry, regulated supply of nitrogen to pressurize the EVAP system. It also provides
smoke to help in locating the leak source. Refer to the directions on the cart for
proper operation.
TheGE-41415-50
Fuel Tank Cap Adapter
is used to adapt theJ 41413-200
to the
fuel filler neck. Pressurizing, or inducing smoke to the EVAP system at the fuel filler
neck allows testing of the filler neck and the fuel fill cap on vehicles with onboard
refueling vapor recovery (ORVR).
TheJ 41413-SPT
High Intensity White
Light is used to help locate the leak source.
On Board Refueling Vapor Recovery (ORVR) System
This vehicle is equipped with an On Board Refueling Vapor Recovery System (ORVR).
This system has developed and equipped to meet enhanced EVAP control requirements
during vehicle moving, parking, and refueling. The ORVR system operates in the following
manner:
| • | One canister collects evaporative vapors while the vehicle is moving,
parking, and refueling. |
| • | Collected vapor flows into the engine through the intake manifold, where
it is consumed during vehicle operation. |
| • | Fuel flowing through a reduced diameter section in the filler pipe creates
suction in the filter neck. |
The ORVR system operates by the liquid trap, liquid seal, system which ensures
long-term durability. The ORVR system has been designed with the following functional
features:
| • | Collection and routing of refueling vapors to the canister |
| • | Nozzles that are compatible with conventional and Stage II vapor
recovery nozzles |
| • | Prevention of liquid fuel entering the canister during normal driving
and during vehicle rollover |
| • | Fuel tank over-pressure prevention |
| • | Fuel tank venting to canister during vehicle operation |
| • | Fuel vapor dome overfill protection |
This vehicle is also equipped with an On Board Diagnostic II (OBD II)
system. This system identifies failures or malfunctions of the ORVR system and warns
the driver through the malfunction indicator lamp (MIL) on the instrument cluster.
The ORVR system requires no special refueling procedures and maintenance.
