0388080 JOHNSON LEAD ASSEMBLY, Ground

Illustration 1 g01106937
Diagram of components for the Hydraulic Electronic Unit Injector(HEUI) fuel system
(1) Unit injector hydraulic pump
(2) Oil filter
(3) Oil cooler
(4) Engine oil pump
(5) HEUI Injectors
(6) Injection Actuation Pressure Control Valve (IAPCV)
(7) Injection Actuation Pressure (IAP) sensor
(8) High pressure oil
(9) Fuel supply rail
(10) Fuel transfer pump
(11) Fuel filter
(12) Fuel tank
(13) Fuel pressure regulator
(14) Back of cam gear
(15) Speed/timing sensors
(16) Fuel/water separator
(17) Electronic Control Module (ECM)
(18) Inlet air pressure sensor
(19) Batteries
(20) Coolant temperature sensor
(21) Inlet air temperature sensor
(22) Oil temperature sensor
(23) Atmospheric pressure sensor
(24) Fuel pressure sensor
(25) Data link
(26) Oil pressure sensor The operation of the HEUI fuel system is completely different from any other type of fuel system that is actuated mechanically. The HEUI fuel system is completely free of adjustment. Adjustments to the components that are mechanical can not be made. Changes in performance are made by installing different software in ECM (17).This fuel system consists of six basic components:
Injectors (5)
ECM (17)
Unit injector hydraulic pump (1)
IAPCV (6)
Fuel Transfer Pump (10)
IAP sensor (7)Note: The components of the HEUI fuel system are not serviceable. These fuel system components must not be disassembled. Disassembly will damage the components. If the components have been disassembled, Caterpillar may not allow a warranty claim or Caterpillar may reduce the warranty claim.Component Description
Hydraulic Electronic Unit Injector
The HEUI fuel system utilizes a hydraulically actuated electronically controlled unit injector (5).All fuel systems for diesel engines use a plunger and barrel in order to pump fuel under high pressure into the combustion chamber. This fuel is pumped into the combustion chamber in precise amounts in order to control engine performance. The HEUI fuel system uses engine oil under high pressure in order to power the plunger. All other fuel systems use a fuel injection pump camshaft lobe in order to power the plunger. Because the HEUI fuel system is much different, a technician must use different troubleshooting methods.The HEUI uses engine lubrication oil that is pressurized from 6 MPa (875 psi) to 27.5 MPa (4000 psi) in order to pump fuel from the injector. The HEUI operates in the same way as a hydraulic cylinder in order to multiply the force of the high pressure oil. By multiplying the force of the high pressure oil, the HEUI can produce injection pressures that are very high. This multiplication of pressure is achieved by applying the force of the high pressure oil to a piston. The piston is larger than the plunger by approximately six times. The piston that is powered by engine lubrication oil under high pressure pushes on the plunger. This engine lubrication oil under high pressure is called the actuation pressure of the oil. The actuation pressure of the oil generates the injection pressure that is delivered by the unit injector. Injection pressure is greater than actuation pressure of the oil by approximately six times.Low actuation pressure of the oil results in low injection pressure of the fuel. During conditions of low speed such as idle and start, low injection pressure is utilized. High actuation pressure of the oil results in high injection pressure of the fuel. During conditions of high speed such as high idle and acceleration, high injection pressure is utilized.There are many other operating conditions when the injection pressure is between the minimum and the maximum. Regardless of the speed of the engine, the HEUI fuel system provides infinite control of injection pressure.ECM
ECM (17) is located on the left side of the engine. The ECM is a powerful computer that provides total electronic control of engine performance. The ECM uses data from engine performance that is gathered by several sensors. Then, the ECM uses this data in order to make adjustments to the fuel delivery, injection pressure and injection timing. The ECM contains programmed performance maps (software) in order to define horsepower, torque curves and rpm. This software is commonly called the personality module.Some engines use ECM (17) with a replaceable computer chip. The software has already been installed in the replaceable computer chip. The engine does not have a replaceable personality module. The engine's personality module is a permanent part of the ECM. The personality module can be reprogrammed. Reprogramming of the personality module requires the use of Caterpillar Electronic Technician (ET). The flash function of Cat ET will be used during the reprogramming. ECM (17) logs faults of engine performance. Also, the ECM is capable of running several diagnostic tests automatically when the ECM is used with Cat ET.Unit Injector Hydraulic Pump
Unit injector hydraulic pump (1) (high pressure oil pump) is located at the left front corner of the engine. The unit injector hydraulic pump is a piston pump that has a fixed displacement. The unit injector hydraulic pump uses an axial piston. The unit injector hydraulic pump uses a portion of the engine lubrication oil. The unit injector hydraulic pump pressurizes the engine lubrication oil to the IAP that is required in order to power injectors (5).IAPCV
IAPCV (6) is located on the side of unit injector hydraulic pump (1). Under most conditions, the pump is producing excess oil flow. The IAPCV discharges excess pump flow to the drain in order to control the IAP to the desired level. The IAPCV is a valve of high precision that controls the actual actuation pressure. The performance maps of ECM (17) contain a desired actuation pressure for every engine operating condition. The ECM sends a control current to the IAPCV. The control current should make the actual actuation pressure equal to the desired actuation pressure.IAPCV (6) is an actuator. The IAPCV converts an electrical signal from ECM (17) to the mechanical control of a spool valve in order to control pump outlet pressure.Fuel Transfer Pump
Fuel transfer pump (10) is mounted on the back of unit injector hydraulic pump (1). The fuel transfer pump is used in order to draw fuel from fuel tank (12). Also, the fuel transfer pump is used in order to pressurize the fuel to 450 kPa (66 psi). The pressurized fuel is supplied to injectors (5).Fuel transfer pump (10) is