- Control module
- Manifold air pressure sensor
- Oxygen sensor
- Oxygen buffer
- Speed sensor (if equipped)
- Temperature sensor
- Fuel valve
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| Illustration 1 | g01386779 |
(1) Control module (2) Manifold air pressure sensor (3) Oxygen sensor (4) Oxygen buffer (5) Speed sensor (magnetic pickup) (6) Temperature sensor (7) Fuel valve | |
Note: Some early applications do not use the speed sensor.
Control Module
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| Illustration 2 | g01417241 |
Control module (8) "POWER" indicator (9) "ALARM" indicator (10) Display (11) Keypad | |
For some applications, four inputs are provided to the control module by sensors on the engine: inlet manifold air pressure, exhaust oxygen level, engine rpm and inlet manifold air temperature. Some applications do not use the engine rpm as an input. The inlet manifold air pressure is a measure of engine load. The exhaust oxygen level is a measure of the exhaust emissions. The engine speed is monitored by a magnetic pickup. The inlet manifold air temperature is an indication of the density of the inlet air. The control uses the inputs to calculate the desired fuel flow.
The system is separate and independent from all of the other engine control systems. When the system is ON, "POWER" indicator (8) is illuminated. The engine can be run with the system in a manual mode or an automatic mode.
If the system detects a diagnostic condition or if the system is in the manual mode, "ALARM" indicator (9) is illuminated.
Display (10) informs the operator of the status of the system. The manifold pressure and oxygen level are continuously updated on the display in both the manual mode and the automatic mode.
The mode is selected with keypad (11). The display and the keypad are the user interface for the air/fuel ratio control. The operator uses the display and the keypad for several functions. The display and the keypad are used for adjustment of the system parameters and for calibration of the oxygen sensor.
When the system is in the automatic mode, the control module moves the fuel valve in order to control the emissions. The automatic control is based on monitoring of the exhaust oxygen level, engine speed, inlet manifold air pressure, and inlet manifold air temperature. The control adjusts the position of the fuel valve in order to maintain a constant exhaust oxygen level.
When the system is in the manual mode, the fuel valve remains in a fixed position. The engine's exhaust emissions can change as the load, the speed, or the ambient conditions change. The manual mode can be useful for adjusting the system and for investigating diagnostics. The manual mode can also be used in case of a problem with a sensor.
Manifold Air Pressure Sensor
The manifold air pressure sensor is mounted in the engine's air inlet manifold. The sensor measures the engine's absolute inlet manifold air pressure. The control uses the information to calculate the engine load. The three-wire sensor has a pulse width modulated signal (PWM) with a width of 500 HZ. The duty cycle is measured by the control and the signal is displayed in absolute kPa.
Oxygen Sensor
The oxygen sensor is mounted above the exhaust elbow. The sensor measures the percent of oxygen in the engine's exhaust. The sensor has a heater. Voltage is input to the sensor and a current signal is output by the sensor to the oxygen buffer.
Oxygen Buffer
An oxygen buffer is mounted on the engine. The buffer provides an interface between the oxygen sensor and the control. The buffer controls the sensor's heater and the supply of voltage to the sensor. The buffer also converts the sensor's output current into a PWM signal with a width of 500 HZ. The control converts the duty cycle into a percent of oxygen.
The signal of the oxygen sensor's duty cycle must be calibrated in order for the control to monitor the actual percent of oxygen in the exhaust. A typical output is a duty cycle of 30 to 65 percent for an oxygen level of 0 to 21 percent.
If there is a problem with the oxygen sensor, the buffer will output a duty cycle of 10 to 20 percent. The control will display a diagnostic message.
Power for the buffer is provided by the control module's output switch. The control only provides power to the buffer when engine operation is detected. The output switch limits the current to five amperes. The switch is protected from excessive current with a shutdown mode that is activated by thermal overload. As the current increases, the switch becomes warmer. If the current becomes excessive, the switch is short circuited. When the switch cools, the short circuit is removed.
Speed Sensor
A magnetic pickup (if equipped) monitors the engine rpm. The signal from the magnetic pickup is a factor that is used by the control to select the targets for the percent of exhaust oxygen.
Temperature Sensor
The temperature sensor is mounted in the engine's air inlet manifold. The sensor monitors the engine's inlet manifold air temperature. The control uses the information as an offset in order to control the exhaust emissions. Cooler inlet manifold air temperatures indicate that more oxygen is present because the air is more dense. More oxygen provides a leaner air/fuel mixture. Warmer inlet manifold air temperatures indicate that less oxygen is present because the air is less dense. Less oxygen provides a richer air/fuel mixture.
Fuel Valve
The fuel valve is located between the gas pressure regulator and the carburetor. The valve improves on the function of the traditional load control valve. The valve is motorized. The motor uses a range of steps that represent the position of the valve. The range of the steps is 0 to 1700. Zero steps represent the fully open position or the richest position. 1700 steps represent the most restricted position or the leanest position.
The control sends a command to the motor in order to move the fuel valve. The control keeps track of the number of steps that are taken. Rather than using a position sensor, the control's tracking provides information on the valve's position.