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Home >> Mazda >> 1994 >> MPV 2WD V6-3.0L SOHC >> Repair and Diagnosis >> Powertrain Management >> Emission Control Systems >> Evaporative Emissions System >> Description and Operation
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Evaporative Emissions System: Description and Operation

Evaporative Emission Control System (EVAP):






PURPOSE
Collect and store fuel vapors that would otherwise be discharged into the atmosphere. Prevents hydrocarbon emissions from evaporated fuel and aids fuel economy by reducing fuel loss through evaporation.

LOCATION
Charcoal canister is in right rear of engine compartment. Purge solenoid is at right front of engine compartment. Separator and check valves are in rear of vehicle.

OPERATION
EVAP system is PCME controlled. The system consists of a vapor separator, purge control solenoid valve, a canister, two-way check valve, check-and-cut valve, vapor separator, PCME, and engine sensors.

PCME monitors operating conditions through various engine sensors and regulates quantity of evaporative gases drawn into the engine with a duty cycle signal to the solenoid valve. System operates when the following conditions are met.

CRUISING (IN FEEDBACK ZONE)
^ Coolant temperature above 140°F (60°C).
^ Driving in gear.
^ Idle switch "OFF."

DECELERATION
^ Idle switch "ON."
^ Coolant temperature above 60°C (140°F).
^ Engine speed above 3500 RPM
^ Transmission in gear


Charcoal Canister
Filled with activated charcoal to condense and store fuel tank gasoline vapors engine is not running.

Separator
Separates fuel vapors from liquid fuel to prevent charcoal canister saturation. Liquid fuel drains back from bottom of separator. Vapors are routed to the canister through the check-and-cut valve and two-way check valve.

Purge Solenoid Valve
Valve is a normally closed solenoid valve. It gets battery power from the main relay when the ignition is turned "ON" and is energized when PCME completes circuit to ground. The solenoid operates on a duty cycle. It is connected in-line between PCV valve and charcoal canister.

Two-Way Check Valve
Prevents charcoal canister fuel vapors from returning to the fuel tank.

Check-And-Cut Valve
Check-and-cut valve has three functions:

^ Vents fuel tank to atmosphere if tank pressure exceeds approx. 0.78 - 1.0 psi (5.37 - 6.87 kPa).
^ Allows air from atmosphere to enter tank if tank pressure is approx. 0.14 - 0.71 psi (0.98 - 4.91 kPa) less than atmospheric.
^ Blocks fuel from leaking through EVAP system if vehicle is overturned.

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