0390691 JOHNSON CARBURETOR ASSY.

Illustration 1 g01790693
Typical view of the ECM
(1) J1/P1 ECM connector
(2) J2/P2 ECM connector The ECM has two connectors. The J1/P1 connector (1) is a 70-pin connector, while the J2/P2 connector (2) is a 120-pin connector. Each pin provides a connection point for a signal interface for the ECM.Overview of the Electronic Control System
The electronic control system is designed to fully control engine operation for optimum performance with minimal emissions.The ECM is the engine control computer for the engine's electronic control system. The ECM provides the capacity for the input/output functions, the control functions, the data link communications, and the computational functionallity for the system. This functionality is detailed below:Input/Output Functions
The ECM relies on several different types of input devices in order to gather information that is related to the current state of engine operation. The ECM receives the status information from the input devices and the ECM then uses the information to calculate the correct output action that is needed in order to control engine operation. These output actions are based on calculations that are made on cumulative data from other system components, software parameters, and information that is related to desired operation. The ECM utilizes switch inputs, sensor inputs,and data link communications to provide input information from the engine components.The ECM provides the following output functions:
Power supply control for related components
Controller circuits for engine operation
Communications ports for communication mediumThe ECM utilizes outputs as power supplies, outputs for high side ECM drivers (switch to battery circuits), outputs for low side ECM drivers (switch to ground circuits), and data link communications to output command signals to other engine controllers.Control Functions
Control functions are typically commands that are derived internally to the ECM circuitry. Control functions are used in order to calculate the necessary effect on the signal status for the output circuits that control the engine operation. The ECM utilizes the output drivers and data link communications to implement control over engine operation.Data Link Communications
The ECM uses two different communication protocols for data link communications:
Cat Data Link
CAN data link (SAE J1939)These two types of data links are the main structure for communication between all of the controllers on the engine and on the machine.The CAN data link is mainly used for communications between the engine ECM and controllers and displays that are on the engine and on the machine. The CAN data link may also be used for communications with Caterpillar Electronic Technician (ET).Communications on the Cat Data Link utilize a Caterpillar proprietary language that is used for communications between Caterpillar proprietary controllers and displays. The Cat Data Link is also used for communications with Cat ET.Computational Functionallity
The computational functionality of the ECM is dedicated to all aspects of engine operation and engine monitoring. The ECM is continuously evaluating the engine's current state of operation. The results are compared by the ECM to the engine's desired state of operation. The ECM evaluates the difference between these two states in order to calculate the necessary control command signals. The ECM then modifies output signals in order to bring the current state of operation closer to the desired state of operation. The ECM also compares the current state of operation to an acceptable range of operation. If the status of any parameter is not within the acceptable range of operation, the ECM communicates the adverse condition to the operator.ECM Software
The ECM software is typically called a flash file. The flash file is a data file that is installed into the ECM. This data file provides the ECM with the software and the data that is needed to run the engine. Occasional updates to the flash file are provided by Caterpillar. The new software files can be downloaded from the Service Information System (SIS) web site. Use Cat ET to download the flash file to the ECM.