The ECM controls the amount of fuel injected by varying signals to the injectors. The injectors will pump fuel only if the injector solenoid is energized. The ECM sends a high voltage signal to energize the solenoid. The energized solenoid lifts the poppet off its seat, closing the oil path to drain and opening the inlet for the high pressure oil. The high pressure oil enters the injector and acts on an intensifier piston, increasing the pressure and injecting fuel. By controlling the timing and duration of the high voltage signal, the ECM can control injection timing and the amount of fuel injected.
The ECM also controls the pressure of the fuel injected into the cylinder by controlling the injection actuation pressure control valve. The injection actuation pressure control valve is a dump valve closely controlling the output pressure of the high pressure oil pump.
The Personality Module inside the ECM sets certain limits on the amount of fuel that can be injected. FRC Fuel Pos is a limit based on boost pressure to control the air/fuel ratio for emissions control. When the ECM senses a higher boost pressure (more air into cylinder), it increases the FRC Fuel Pos limit (allows more fuel into cylinder).
Rated Fuel Pos is a limit based on the power rating of the engine and rpm. It is similar to the rack stops and torque spring on a mechanically governed engine. It provides power and torque curves for a specific engine family and rating. All of these limits are determined at the factory in the Personality Module and cannot be changed in the field. Injection timing depends on engine rpm, load and other operating factors.
Injection Actuation Pressure System
The ECM controls fuel injection by controlling oil. The pressure of the oil in the high pressure oil manifold is controlled by the ECM through control of the injection actuation pressure control valve. The injection actuation pressure control valve (dump valve) controls the high pressure pump outlet pressure by dumping excess flow back to the oil sump.
The ECM monitors the pressure in the high pressure manifold through the injection actuation pressure sensor. The injection actuation pressure sensor is located in the top of the manifold on the left side of the engine. The injection actuation pressure sensor signal (Inj Act Pr) is compared by the ECM to the desired injection actuation pressure (Des Inj Act Pr). The ECM determines the Des Inj Act Pr based on several inputs and changes the position of the injection actuation pressure control valve (Inj Act Output) to adjust the oil pressure in the high pressure manifold.
High pressure oil is routed from the pump to the high pressure manifold through a steel tube. From the manifold the oil is routed to each injector through short jumper tubes. All injectors have a constant supply of oil while the engine is running. Cutting out an injector disables the electrical signal to the injector solenoid, but does not interrupt the oil flow to the injector.