Evaporative Emission Control System Operation - Daewoo CIELO EURO III Manual

the MAP sensor and read by the ECM, which then
decreases the fuel injector on-time due to the low fuel
demand conditions.
The O2S 1 sensor is located in the exhaust manifold.
The O2S 1 sensor indicates to the ECM the
amount of oxygen in the exhaust gas and the ECM
changes the air/fuel ratio to the engine by controlling the
fuel injectors. The best air/fuel ratio to minimize exhaust
emissions is 14.7 to 1, which allows the catalytic con-
verter to operate most efficiently. Because of the
constant measuring and adjusting of the air/fuel ratio,
the fuel injection system is called a "closed loop" sys-
tem.
The ECM uses voltage inputs from several sen-
sors to determine how much fuel to provide to the en-
gine. The fuel is delivered under one of several
conditions, called "modes."
Starting Mode
When the ignition is turned ON, the ECM turns the
fuel pump relay on for two seconds. The fuel pump then
builds fuel pressure. The ECM also checks the En-
gine Coolant Temperature (ECT) sensor and the
Throttle Position (TP) sensor and determines the proper
air/fuel ratio for starting the engine. This ranges from 1.5
to 1 at *36_C (*33_F) coolant temperature to 14.7 to 1
at 94_C (201_F) coolant temperature. The ECM
controls the amount of fuel delivered in the starting
mode by changing how long the fuel injector is turned on
and off. This is done by "pulsing" the fuel injectors for
very short times.
Clear Flood Mode
If the engine floods with excessive fuel, it may be
cleared by pushing the accelerator pedal down all the
way. The ECM will then completely turn off the fuel
by eliminating any fuel injector signal. The ECM
holds this injector rate as long as the throttle stays wide
open and the engine is below approximately 400 rpm. If
the throttle position becomes less than approximately
80%, the ECM returns to the starting mode.
Run Mode
The run mode has two conditions called "open loop" and
"closed loop."
Open Loop
When the engine is first started and it is above 400 rpm,
the system goes into "open loop" operation. In "open
loop," the ECM ignores the signal from the O2S 1
and calculates the air/fuel ratio based on inputs from the
ECT and the MAP sensors. The sensor stays in "open
loop" until the following conditions are met:
D The O2S 1 sensor has a varying voltage output,
showing that it is hot enough to operate properly.
D The ECT sensor is above a specified temperature.
D A specific amount of time has elapsed after starting
the engine.
DAEWOO T-154 BL2,3
ENGINE CONTROLS 1F – 411
Closed Loop
The specific values for the above conditions vary with
different engines and are stored in the electrically eras-
able programmable read-only memory (EEPROM).
When these conditions are met, the system goes into
"closed loop" operation. In "closed loop," the ECM
calculates the air/fuel ratio (fuel injector on-time) based
on the signal from the oxygen sensor. This allows the
air/fuel ratio to stay very close to 14.7 to 1.
Acceleration Mode
The ECM responds to rapid changes in throttle
position and air flow and provides extra fuel.
Deceleration Mode
The ECM responds to changes in throttle position
and air flow and reduces the amount of fuel. When de-
celeration is very fast, the ECM can cut off fuel
completely for short periods of time.
Battery Voltage Correction Mode
When battery voltage is low, the ECM can com-
pensate for a weak spark delivered by the ignition mod-
ule by using the following methods:
D Increasing the fuel injector pulse width.
D Increasing the idle speed rpm.
D Increasing the ignition dwell time.
Fuel Cut-Off Mode
No fuel is delivered by the fuel injectors when the ignition
is OFF. This prevents dieseling or engine run-on. Also,
the fuel is not delivered if there are no reference pulses
received from the CKP sensor. This prevents flooding.
EVAPORATIVE EMISSION CONTROL
SYSTEM OPERATION
The basic evaporative (EVAP) emission control system
is a duty control linear type and uses the EVAP emission
canister storage method. This method transfers fuel va-
por from the fuel tank to an activated carbon (charcoal)
canister to hold the vapors when the vehicle is not oper-
ating. When the engine is running, the fuel vapor is
purged from the carbon element by intake airflow and
consumed in the normal combustion process.
Gasoline vapors from the fuel tank flow into the tube la-
beled TANK. These vapors are absorbed into the car-
bon. The canister is purged by the
engine control module (ECM) when the
engine has been running for a specified amount of time.
Air is drawn into the canister and mixed with the vapor.
This mixture is then drawn into the intake manifold.
The ECM supplies a ground to energize the EVAP
emission canister purge solenoid valve. This valve is
Pulse Width Modulated (PWM) or turned on and off sev-
eral times a second. The EVAP emission canister purge
PWM duty cycle varies according to operating condi-