826380 Force SCREW (.250-20 x .625)

Illustration 1 g00457847
Diagram of components for the HEUI fuel system (1) Unit injector hydraulic pump (2) Oil flow to engine (3) Oil filter (4) Engine oil pump (5) Oil cooler (6) IAP sensor (7) Injectors (8) Fuel supply rail (9) Fuel pressure regulator (10) IAP control valve (11) Fuel filter (12) Fuel tank (13) Back of cam gear (14) Speed/timing sensors (15) ECM (16) Boost pressure sensor (17) Accelerator pedal (18) Accelerator pedal position sensor (19) Batteries (20) Coolant temperature sensor (21) Data link (22) Exhaust brake relay (23) Inlet air temperature sensor (24) Transmission relay (25) Vehicle speed sensor (26) Inlet air heater relay (27) Inlet air heater lamp (28) Fast idle lamp (29) Check engine lamp (30) Speedometer and tachometer (31) Cruise ON/OFF switch and Cruise SET/RESUME switch (32) PTO ON/OFF switch and SET/RESUME switch (33) Service brake switches (34) Neutral and clutch switches (35) Fuel transfer pumpThe operation of the Hydraulic Electronic Unit Injector (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 Engine Control Module (ECM) (15) .This fuel system consists of six basic components:
Hydraulic Electronic Unit Injector (HEUI) (7)
Engine Control Module (ECM) (15)
Unit injector hydraulic pump (1)
Injection Actuation Pressure Control Valve (10)
Fuel Transfer Pump (35)
Injection Actuation Pressure Sensor (6) 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 (7) .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 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 is much different, a technician must use different troubleshooting methods.The HEUI uses engine lubrication oil that is pressurized from 6 MPa (870 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.Engine Control Module (ECM)
Engine Control Module (ECM) (15) 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 Engine Control Modules (ECM) (15) with a replaceable computer chip. The software has already been installed in the replaceable computer chip. The 3126B and 3126E diesel truck engines do not have a replaceable personality module. The 3126B and 3126E diesel truck engine's personality module are a permanent part of the ECM. The 3126B and 3126E diesel truck engine's personality module can be reprogrammed. Reprogramming of the personality module requires the use of Caterpillar Electronic Technician (Cat ET). The flash function of Cat ET will be used during the reprogramming. ECM (15) logs faults of engine performance. Also, the ECM is capable of running several diagnostic tests automatically when the ECM is used with an electronic service tool such as the 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 injection actuation pressure that is required in order to power the HEUI injectors.Injection Actuation Pressure Control Valve (IAP Control Valve)
Injection actuation pressure control valve (10) (IAP Control Valve) is located on the side of unit injector hydraulic pump (1). Under most conditions, the pump is producing excess oil flow. The IAP Control Valve discharges excess pump flow to the drain in order to control injection actuation pressure to the desired level. The IAP Control Valve is a valve of high precision that controls the