Evaporative Emissions
Emissions Management
Evaporative Emissions
The control of the evaporative fuel vapors (Hydrocarbons) from the fuel tank is important for the over-all reduction in vehicle emissions.
The evaporative system has been combined with the ventilation of the fuel tank, which allows the tank to breath (equalization). The overall operation provides:
- An inlet vent, to an otherwise "sealed" fuel tank, for the entry of air to replace the fuel consumed during engine operation.
- An outlet vent with a storage canister to "trap and hold" fuel vapors that are produced by the expansion/evaporation of fuel in the tank, when the vehicle is stationary.
The canister is then "purged" using the engine vacuum to draw the fuel vapors into the combustion chamber. This "cleans" the canister allowing for additional storage. Like any other form of combustible fuel, the introduction of these vapors on a running engine must be controlled. The ECM controls the Evaporative Emission Valve which regulates purging of evaporative vapors.
ON-BOARD REFUELING VAPOR RECOVERY (ORVR)
The ORVR system recovers and stores hydrocarbon fuel vapor that was previously released during refueling. Non ORVR vehicles vent fuel vapors from the tank venting line back to the filler neck and in many states reclaimed by a vacuum receiver on the filling station's fuel pump nozzle.
When refueling, the pressure of the fuel entering the tank forces the hydrocarbon vapors through the tank vent line to the liquid/ vapor separator, through the rollover valve and into the charcoal canister.
The HC is stored in the charcoal canister, and the system can then "breath" through the DMTL and the air filter.
Liquid/Vapor Separator
Fuel vapors are routed from the fuel tank filler neck through a hose to the Liquid/Vapor Separator (located in the right rear wheel well behind the trim).
The vapors cool when exiting the fuel tank, the condensates separate and drain back to the fuel tank through a return hose (1).The remaining vapors exit the Liquid/Vapor Separator to the Active Carbon Canister.
Active Carbon Canister
As the fuel vapors enter the canister, they will be absorbed by the active carbon. The remaining air will be vented to the atmosphere through the end of the canister (passing through the DMTL and filter) allowing the fuel tank to "breath".
When the engine is running, the canister is then "purged" using intake manifold vacuum to draw fresh air through the canister which extracts the hydrocarbon vapors into the combustion chamber. This cleans the canister for additional storage. The Active Carbon Canister is located under the luggage compartment floor with the DM TL Pump.
Evaporative Emission Valve
This ECM controlled solenoid valve (located under the intake manifold) regulates the purge flow from the Active Carbon Canister through the idle air distribution pipe into the intake manifold .
The ECM Relay provides operating voltage, and the ECM controls the valve by regulating the ground circuit. The valve is powered open and closed by an internal spring.
If the Evaporative Emission Valve circuit is defective, a fault code will be set and the "Malfunction Indicator Light" will be illuminated. If the valve is "mechanically" defective, a driveability complaint could be encountered and a mixture related fault code will be set.
DM TL (Diagnosis Module - Evaporative Leakage Detection): This component ensures accurate fuel system leak detection for leaks as small as 1.0 mm (.040°)by slightly pressurizing the fuel tank and evaporative components. The DM TL pump contains an integral DC motor which is activated directly by the ECM. The ECM monitors the pump motor operating current as the measurement for detecting leaks.
The pump also contains an ECM controlled change over valve that is energized closed during a Leak Diagnosis test. The change over valve is open during all other periods of operation allowing the fuel system to "breath" through the inlet filter. The DM TL is located under the luggage compartment floor with the Active Carbon Canister.
1. In its inactive state, filtered fresh air enters the evaporative system through the sprung open DM TL valve.
2. When the DME activates the DM TL for leak testing, it first activates only the pump motor. This pumps air through a restricted orifice (1.0 mm) which causes the electric motor to draw a specific amperage value. This value is equivalent to the size of the restriction.
3. The solenoid valve is then energized which seals the evaporative system and directs the pump output to pressurize the evaporative system.
- A large leak is detected in the evaporative system if the amperage value is not achieved.
- A small leak is detected if the same reference amperage is achieved.
- The system is sealed if the amperage value is higher than the reference amperage.
Starting with 2002 MY, a heating element was added to the DMTL pump to eliminate condensation. The heater is provided battery voltage when KL15 is switched "on" and the ECM provides the ground path.