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1F2 -- 40 M161 ENGINE CONTROLS DAEWOO MY_2000 FUEL SYSTEM The function of the fuel metering system is to deliver the correct amount of fuel to the engine under all operating condi- tions. The fuel is delivered to the engine by the individual fuel injectors mounted into the intake manifold near each cylinder. mounted in the intake air stream, where it is cooled by the flow of incoming air. Engine Control Module (ECM) modu- lates the flow of heating current to maintain the temperature differential between the heated film and the intake air at a constant level. The amount of heating current required to maintain the temperature thus provides an index for the mass air flow. This concept automatically compensates for variations in air density, as this is one of the factors that determines the amount of warmth that the surrounding air absorbs from the heated element. MAF sensor is located between the air filter and the throttle valve. uses this information to enrich the mixture, thus increasing the fuel injector on--time, to provide the correct amount of fuel. When decelerating, the mass flow decreases. This mass flow change is sensed by the MAF sensor and read by the ECM, which then decreases the fuel injector on--time due to the low fuel demand conditions. 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 converter 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” system. 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 1 second. The fuel pump then builds fuel pressure. The ECM also checks the Engine 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. 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 690 rpm, the system goes into “open loop” operation. In “open loop”, the ECM ignores the signal from the HO2S and calculates the air/fuel ratio based on inputs from the ECT sensor and the MAF sensor. The ECM stays in “open loop” until the following conditions are met: The O2 has a varying voltage output, showing that it is hot enough to operate properly. D The ECT sensor is above a specified temperature (22.5 °C). D A specific amount of time has elapsed after starting the engine. Closed Loop The specific values for the above conditions vary with different engines and are stored in the Electronically Erasable 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 signals from the O2 sensors. 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 airflow and provides extra fuel. Deceleration Mode The ECM responds to changes in throttle position and airflow and reduces the amount of fuel. When deceleration is very fast, the ECM can cut off fuel completely for short periods of time. |