Fuel Control Basics

FUEL SYSTEM - GENERAL INFORMATION

WARNING: HIGH-PRESSURE FUEL LINES DELIVER DIESEL FUEL UNDER EXTREME PRESSURE FROM THE INJECTION PUMP TO THE FUEL INJECTORS. THIS MAY BE AS HIGH AS 23,200 PSI (1600 BAR). USE EXTREME CAUTION WHEN INSPECTING FOR HIGH-PRESSURE FUEL LEAKS. FUEL UNDER THIS AMOUNT OF PRESSURE CAN PENETRATE SKIN CAUSING PERSONAL INJURY OR DEATH. INSPECT FOR HIGH-PRESSURE FUEL LEAKS WITH A SHEET OF CARDBOARD. WEAR SAFETY GOGGLES AND ADEQUATE PROTECTIVE CLOTHING WHEN SERVICING FUEL SYSTEM.

The fuel system is a Robert Bosch High Pressure Common Rail (HPCR) electronically controlled fuel system. The HPCR system consists of five main components:
* Electronic Fuel Lift Pump
* Fuel Pump Gear Pump
* High Pressure Pump (CP3)
* Fuel Rail
* Injectors

The High Pressure Pump (CP3) supplies high-pressure fuel to the fuel rail independent of engine speed. This high-pressure fuel is then accumulated in the Fuel Rail. High-pressure fuel is constantly supplied to the Injectors by the Fuel Rail. The Electronic Control Module (ECM) controls the fueling and timing of the engine by actuating the Injectors.

Fuel enters the system from the Electronic Fuel Lift Pump, which is attached to the fuel filter assembly. Fuel is forced through the fuel filter element and then enters the Fuel Pump Gear Pump, which is attached to the rear of the High Pressure Pump (CP3). The Fuel Pump Gear Pump is a low-pressure pump and produces pressures ranging from 80 - 180 psi (5.5 - 12.4 bar).

Then the fuel enters the High Pressure Pump (CP3). The low-pressure fuel is then supplied to the Fuel Control Actuator (FCA). The Fuel Control Actuator is an electronically controlled solenoid valve. The ECM controls the amount of fuel that enters the high pressure pumping chambers by opening and closing the Fuel Control Actuator based on a demanded fuel pressure. The Pressure Sensor on the Fuel Rail provides the actual fuel pressure. when the Actuator is opened, the maximum amount of fuel is being supplied to the High Pressure Pump. Any fuel that does not enter the High Pressure Pump is directed to the Cascade Overflow Valve. The Cascade Overflow Valve regulates how much excess fuel is used for lubrication for the pump and how much is returned to the tank.

The fuel that enters the High Pressure Pump is pressurized between 4350 - 23,200 psi (300 - 1600 bar) by three radial pumping chambers. The pressurized fuel is then supplied to the Fuel Rail.