87123-881-A21 Honda SEE PART DETAILS - PRI; LABEL, INDICATION (E) (Honda Code 7536287).

System Operation
Engine Governor
The ECM governs the engine. The ECM determines the timing, the injection pressure, and the amount of fuel that is delivered to each cylinder. These factors are based on the actual conditions and on the desired conditions at any given time during starting and operation.For variable speed engines, the ECM uses the throttle position sensor to determine the desired engine speed. The ECM compares the desired engine speed to the actual engine speed. The actual engine speed is determined through interpretation of the signals that are received by the ECM from the engine speed/timing sensors.Timing Considerations
Once the ECM has determined the amount of fuel that is required, the ECM must determine the timing of the fuel injection.The ECM adjusts timing for optimum engine performance and for the fuel economy. Actual timing and desired timing cannot be viewed with the electronic service tool. The ECM determines the location of top center of the number one cylinder from the signals that are provided by the engine speed/timing sensors. The ECM determines when injection should occur relative to the top dead center position. The ECM then provides the signal to the injector at the correct time.Fuel Injection
The high-pressure fuel system is controlled by the ECM. The ECM gathers data from several sensors on the engine. The ECM then uses this data to adjust the quantity of fuel being delivered as well as the timing of the injection event. The injection event begins when the ECM sends a signal to the injector solenoid to actuate the valve inside the injector. As the valve opens, the fuel flows from the fuel manifold (rail), through the fuel line, and into the injector. As the valve opening pressure is reached, the valve is lifted and the fuel is delivered at high pressure into the combustion chamber.The flash file inside the ECM establishes certain limits on the amount of fuel that can be injected. The "Smoke Limit Fuel" is a limit that is based on the intake manifold pressure. The "Smoke Limit Fuel" is used to control the air/fuel ratio for control of emissions. When the ECM senses a higher intake manifold pressure, the ECM increases the "Smoke Limit Fuel". A higher intake manifold pressure indicates that there is more air in the cylinder. When the ECM increases the "Smoke Limit Fuel", the ECM changes the control signal to the injector. The signal will allow more fuel into the cylinder.The "Torque Limit Fuel" is a limit that is based on the power rating of the engine and on the engine rpm. The "Torque Limit Fuel" is like the rack stops and the torque spring on a mechanically governed engine. The "Torque Limit Fuel" provides the power curves and the torque curves for a specific engine family and a specific engine rating. All these limits are determined at the factory. These limits cannot be changed.Other ECM Functions for Performance
The ECM may also provide enhanced control of the engine for functions such as controlling the cooling fan. Refer to Troubleshooting, "Configuration Parameters" for supplementary information about the systems that can be monitored and controlled by the ECM.Programmable Parameters
Certain parameters that affect engine operation may be changed with the electronic service tool. The parameters are stored in the ECM, and the parameters are protected from unauthorized changes by passwords. These parameters are either system configuration parameters or customer parameters.System configuration parameters are set at the factory. System configuration parameters affect emissions or power ratings. Factory passwords must be obtained and factory passwords must be used to change the system configuration parameters.Some of the parameters may affect engine operation in an unusual way. An operator might not expect this type of effect. Without adequate training, these parameters may lead to power complaints or performance complaints even though the engine performance is within the specification.Customer parameters can be used to affect the characteristics of the engine. Limits are set by the factory and by the monitoring system.Customer passwords may be required to change customer specified parameters.Refer to Troubleshooting, "Configuration Parameters" for additional information on this subject.Passwords
System configuration parameters are protected by factory passwords. Factory passwords are calculated on a computer system that is available only to Caterpillar dealers. Since factory passwords contain alphabetic characters, only the electronic service tool can be used to change system configuration parameters.Customer parameters can be protected by customer passwords. The customer passwords are programmed by the customer. Factory passwords can be used to change customer passwords if customer passwords are lost.Refer to Troubleshooting, "Customer Passwords" and Troubleshooting, "Factory Passwords" for additional information on this subject.