BUSHING-REDUCER 3B7257 - Caterpillar

The engine electronic control group for the air/fuel ratio is a digital control for use with low emission engines that use natural gas with one gas pressure regulator and a carburetor. This system can be configured in the field with the keypad that is on the control module. The settings of the control module and the system diagnostics are designed to control the fuel system in order to maintain operation at reduced emission levels. The system consists of seven basic components:
Control module
Manifold air pressure sensor
Oxygen sensor
Oxygen buffer
Speed sensor (if equipped)
Temperature sensor
Fuel valve
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 valveNote: Some early applications do not use the speed sensor.Control Module
Illustration 2 g01417241
Control module (8) "POWER" indicator (9) "ALARM" indicator (10) Display (11) KeypadFor 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