Evaporative Emission Control System Description (K07 UFM)

Evaporative Emission Control System Description (LC8\ K07\ UFM)

This description deals with the 3 tank (UFM) liquid propane gas (LPG) - (K07) system.

EVAP System Operation

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. During engine Off mode a vacuum pump pulls fuel vapor from the engine and stores them in the EVAP canister. At an appropriate time, the engine control module (ECM) will command the EVAP purge solenoid valve ON, allowing engine vacuum to be applied to the EVAP canister.

Fresh air is drawn through a hose spliced into the PCV system then 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 tube and EVAP purge solenoid valve into the intake manifold to be consumed during normal combustion.

The purge solenoid valve, controlled by the ECM, will purge fuel vapors during engine run mode. This is separate from and not to be confused with the purge mode described under Fuel System Description (LC8,K07,UFM), Fuel System Overview.

EVAP System Components

Note: The conventional EVAP control system on this LPG fueled vehicle has been disabled. Many of the components are removed with the exception of the EVAP purge solenoid valve. All the associated EVAP DTC's have also been turned off and therefore there is no scan tool support for this LPG system.

Note: The liquid propane injection system utilizes a unique EVAP sub-system to maintain compliant levels of evaporative emissions. The system consists of the addition of vapor lines and a vacuum pump controlled by the LPG Control Module.

The EVAP system consists of the following components:

EVAP Purge Solenoid Valve

The EVAP purge solenoid valve controls the flow of vapors from the EVAP sub-system to the intake manifold. The purge solenoid valve opens when commanded ON by the ECM. This normally closed valve is pulse width modulated (PWM) by the ECM to precisely control the flow of fuel vapor to the engine.

EVAP Canister

The canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapor is stored in the canister until the ECM determines that the vapor can be consumed in the normal combustion process.

Vacuum Pump

The vacuum pump is housed in a protective box and mounted on a bracket next to the EVAP canister. Additional vapor lines are spliced into the purge and PCV lines to complete this sub-system. When the engine is off, the vacuum pump moves fuel rich vapor from the engine to the EVAP canister for storage. The system operates during this engine off mode when the following criteria is met.

1. Ignition Off for 20 min

2. Battery voltage greater than 10.8 V

3. Pump On for 2 min

4. Pump Off for up to 20 min

5. Steps 3 and 4 repeat for up to 110 h or battery voltage less than 10.8 V

This will reset when the ignition key is cycled on.