The TWV (2) receives signals from the engine control module (ECM) and opens and closes to change the pressure in the pressure adjustment chamber (5) on top of the hydraulic piston (6). This allows the hydraulic piston to work and allows the fuel to be injected from the nozzle (8).

Action of Injector -- Non Injection

When there is no continuity to the two-way valve (TWV) with the outer valve down, outer seat closed, the piston is commanded down, pushing the nozzle downward to close the injection hole. This ensures that the fuel pressure does not escape from the control chamber.

Action of Injector -- Injection Start

When there is continuity to the TWV with the outer valve up, outer seat open, the piston is commanded up moving the nozzle upward to open the injection holes. This allows the fuel pressure to escape from the control chamber. This type of injection is conducted twice. First, only injecting a small amount of fuel, pilot injection, and second injecting fuel when combustion occurs, main injection.

Action of Injector -- Injection Finish

When there is no continuity to the TWV with the outer valve down, outer seat closed, the piston is commanded down, pushing the nozzle further downward to close the injection hole. This eliminates the possibility of fuel pressure escaping from the control chamber.

Important: Do not open the fuel supply pump and injector assembly, as this will void the manufacturers warranty.

The electronically controlled fuel injection system consists of the following:

The fuel supply pump has an identification tag (1) attached to the fuel supply pump body.

The common rail system detects engine conditions such as:

Engine conditions are detected by means of common rail sensors and affects fuel injection amount, timing, and pressure. This is controlled by the engine control module (ECM) which ensures the best running condition for the engine.

The system performs the self-diagnosis lamp lighting function to help diagnose main components. This self diagnosis can serve as a driver warning as well. Built into the system is a backup function which automatically switches over to a control function. This function ensures the vehicle will run continuously.

The system can be divided into two systems, fuel and control.

Fuel System

The high pressure fuel generated by the supply pump is distributed to each cylinder. The solenoid valve in the injector opens and closes the injector needle valve, thereby controlling the start and end of fuel injection.

Control System

The engine control module (ECM) is used to compute electric passing timing and electric supply time by using signals from the sensors which are installed on the engine and vehicle. This controls the optimum fuel injection quantity and timing.

The control system is comprised mainly of sensors, ECM, and actuators.

The common rail system hardware consists of:

The supply pump generates the fuel pressure in the common rail. Fuel pressure is controlled depending on the fuel amount discharged from the supply pump. The fuel discharge amount is controlled by means of a pressure control valve (PCV) provided in the supply pump which is opened/closed in response to electric signals from the ECM.

The common rail receives and distributes the fuel pressure made by the supply pump to each cylinder. Fuel pressure is detected by means of a common rail pressure sensor. This is feedback controlled so that the instructed pressure value is set according to the engine speed and load which should agree with the actual pressure value.

The fuel pressure in the common rail is applied through the injection pipe of each cylinder to the injector side and control chamber of the injector.

The injector controls injection amount and time by switching a two-way valve (TWV) ON and OFF . When the TWV is switched ON high pressure fuel in the control chamber flows out through the outlet orifice. The needle valve is lifted to start fuel injection when the injector valve opening is forced up by the high pressure fuel. When the TWV is switched OFF high pressure fuel flows back through the inlet orifice into the control chamber. The needle valve comes down to stop fuel injection. The fuel injection time and amount can be electronically controlled by the TWV switching ON and OFF.

The engine control module (ECM) computes fuel requirements by signals coming from sensors installed to both the engine and vehicle. The ECM also controls the time point and length for carrying current to the injector so that the optimum injection can be performed at the optimum timing.

Fuel Pilot Injection Control Function

This function controls the fuel pilot injection.

Fuel Injection Amount Control Function

This is a function to control fuel injection based on signals from engine speed and accelerator opening sensors so that the optimum injection amount can be obtained. This can be known as a substitute for the conventional mechanical governor.

Fuel Injection Timing Control Function

This is a function to obtain the optimum injection timing from the engine speed and the fuel injection amount. This is a substitute for the conventional timer.

Fuel Injection Pressure Control Function (Common Rail Pressure Control Function)

This is a function to measure fuel pressure with the common rail sensor and feedback the measurement to the ECM in order to control the discharge amount of the pump. Pressure feedback controls is carried out so that the optimum value, instructed value, is set according to the engine speed and fuel injection amount.