Mixture Control Solenoids
The more advanced feedback systems used electrical solenoids to control the metering rods. These solenoids are generally referred to as duty-cycle solenoids or mixture control (M/C) solenoids. The solenoid is normally wired through the ignition switch and grounded through the PCM. The solenoid is energized when the PCM supplies a ground for it. The PCM cycles the solenoid ten times per second. Each cycle lasts 100 milliseconds. The amount of fuel metered into the main fuel well is determined by how many milliseconds the solenoid is on during each cycle. The solenoid can be on almost 100% of the cycle, or it can be off nearly 100% of the time. The MC solenoid can control a fuel metering rod, an air bleed, or both.
Duty CycleOn some computer-controlled carburetor systems, the computer grounds the o, feedback solenoid winding at a constant rate, called duo cycle. Although the duty cycle remains constant, the computer has the capability to change the length of time that the solenoid winding remains grounded. This is referred to as dwell time or on-time. For example, if a manifold vacuum leak is making the air/fuel ratio lean, the computer receives a continuously low 02 sensor voltage. When this continually lean signal is received, the computer provides a rich command to the 02 feedback solenoid winding. This rich command reduces the 02 feedback dwell time and leaves the solenoid plunger up longer to try to provide a stoichiometric air/fuel ratio. under this condition, the computer may leave the solenoid winding off for 90% of the time and on for 10% of the time on each cycle. The computer operates the 02 feedback solenoid to maintain the air/fuel ratio at stoichiometric under most operating conditions. If the 02 sensor sends a continually rich signal to the computer, the computer provides a lean command to the 02 feedback solenoid. When this action occurs, the computer may keep the solenoid winding on for 90% of the time and off for 10% of the time on each cycle to bring the mixture to the stoichiometric ratio.
Idle System Air/Fuel Ratio ControlThe computer and the 02 feedback solenoid also control he air/fuel ratio when the engine is idling. An air passage extends from the top of the solenoid plunger into the idle system. When the solenoid plunger is moved upward, the top of the plunger blocks the air passage into the idle system, which provides a richer idle air/fuel ratio. If the computer grounds the solenoid winding and moves the plunger downward, the air passage is opened past the top of the plunger into the idle system. Under this condition, he idle air/fuel ratio is leaner. If a defect occurs in the 02 feedback system so that the computer no longer operates the 02 feedback solenoid, the spring moves the plunger upward and the air/fuel mixture is continually rich. Under this condition, fuel economy and performance are reduced and emissionlevels increase, but the vehicle can be driven to a service center.
The more advanced feedback systems used electrical solenoids to control the metering rods. These solenoids are generally referred to as duty-cycle solenoids or mixture control (M/C) solenoids. The solenoid is normally wired through the ignition switch and grounded through the PCM. The solenoid is energized when the PCM supplies a ground for it. The PCM cycles the solenoid ten times per second. Each cycle lasts 100 milliseconds. The amount of fuel metered into the main fuel well is determined by how many milliseconds the solenoid is on during each cycle. The solenoid can be on almost 100% of the cycle, or it can be off nearly 100% of the time. The MC solenoid can control a fuel metering rod, an air bleed, or both.
Duty CycleOn some computer-controlled carburetor systems, the computer grounds the o, feedback solenoid winding at a constant rate, called duo cycle. Although the duty cycle remains constant, the computer has the capability to change the length of time that the solenoid winding remains grounded. This is referred to as dwell time or on-time. For example, if a manifold vacuum leak is making the air/fuel ratio lean, the computer receives a continuously low 02 sensor voltage. When this continually lean signal is received, the computer provides a rich command to the 02 feedback solenoid winding. This rich command reduces the 02 feedback dwell time and leaves the solenoid plunger up longer to try to provide a stoichiometric air/fuel ratio. under this condition, the computer may leave the solenoid winding off for 90% of the time and on for 10% of the time on each cycle. The computer operates the 02 feedback solenoid to maintain the air/fuel ratio at stoichiometric under most operating conditions. If the 02 sensor sends a continually rich signal to the computer, the computer provides a lean command to the 02 feedback solenoid. When this action occurs, the computer may keep the solenoid winding on for 90% of the time and off for 10% of the time on each cycle to bring the mixture to the stoichiometric ratio.
Idle System Air/Fuel Ratio ControlThe computer and the 02 feedback solenoid also control he air/fuel ratio when the engine is idling. An air passage extends from the top of the solenoid plunger into the idle system. When the solenoid plunger is moved upward, the top of the plunger blocks the air passage into the idle system, which provides a richer idle air/fuel ratio. If the computer grounds the solenoid winding and moves the plunger downward, the air passage is opened past the top of the plunger into the idle system. Under this condition, he idle air/fuel ratio is leaner. If a defect occurs in the 02 feedback system so that the computer no longer operates the 02 feedback solenoid, the spring moves the plunger upward and the air/fuel mixture is continually rich. Under this condition, fuel economy and performance are reduced and emissionlevels increase, but the vehicle can be driven to a service center.
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