850938 Volvo.Penta Emblem

Illustration 1 g00990048
HEUI fuel system (typical example)
(1) Unit injector hydraulic pump
(2) Oil flow to the engine
(3) Oil filter
(4) Engine oil pump
(5) Injectors
(6) Oil cooler
(7) IAP control valve
(8) IAP sensor
(9) Fuel transfer pump
(10) Secondary fuel filter
(11) Fluid manifolds
(12) Fuel tank
(13) Fuel pressure regulator
(14) Speed-timing wheel
(15) Engine speed/timing sensors
(16) Primary fuel filter
(17) Water separator
(18) Oil temperature sensor
(19) Engine boost pressure sensor
(20) Coolant temperature sensor
(21) Coolant level sensor
(22) Oil pressure sensor
(23) Fuel pressure sensor
(24) Fuel temperature sensor
(25) Atmospheric pressure sensor
(26) Throttle position sensor
(27) Data link
(28) Alarm warning lamp
(29) Diagnostic lamp
(30) Electronic Control Module (ECM)
(31) BatteriesThe operation of the Hydraulic Electronic Unit Injector (HEUI) fuel system utilizes the concepts of hydraulics and the multiplication of force to deliver fuel to the engine. The HEUI fuel system is completely free of adjustment. Adjustments cannot be made to the mechanical components of the system. Changes in performance are made by installing different software in Electronic Control Module (ECM) (30).This fuel system consists of six basic components:
Hydraulic Electronic Unit Injector (HEUI) (5)
Electronic Control Module (ECM) (30)
Unit injector hydraulic pump (1)
Injection actuation pressure control valve (7)
Fuel transfer pump (9)
Injection actuation pressure sensor (8)Note: The components of the HEUI fuel system are not serviceable components. 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).The precise delivery of the fuel controls the engine's performance. All fuel systems for diesel engines use a plunger and barrel in order to pump high pressure fuel into the combustion chamber. A fuel injection pump camshaft lobe is typically used to provide a mechanical force to the plunger. The plunger then pumps the precise amount of fuel into the combustion chamber. The HEUI fuel system uses engine oil that has been pressurized by the system's hydraulic pump in order to apply force to the plunger. Control for the exact timing of the fuel delivery is provided electronically by the engine's ECM. Due to the differences in the HEUI fuel system, a technician must use different troubleshooting methods in order to diagnose fuel system problems.The HEUI fuel system's hydraulic pump pressurizes the engine lubrication oil from 10 MPa (1450 psi) to 23 MPa (3350 psi) in order to transfer force from the engine's rotational energy to hydraulic energy that is used by the injector. The HEUI fuel system operates in the same manner as a hydraulic cylinder. A piston in the injector is used to receive the hydraulic energy that is supplied by the pump. The piston converts the hydraulic energy to a mechanical force that is applied directly to the injector's plunger assembly. The plunger assembly multiplies the mechanical force that is provided by the piston. The plunger converts the force into a hydraulic pressure that is placed on the fuel that is in the injector barrel. By multiplying the force of the high pressure oil that is supplied by the HEUI fuel system's hydraulic pump, the HEUI can produce the injection pressures that are essential for the complete fuel atomization that provides combustion efficiency.Engine oil is used by the unit injector hydraulic pump in order to supply hydraulic pressure to the injectors. This hydraulic pressure is called injector actuation pressure. The actuation pressure of the oil generates the high injection pressures that are delivered by the unit injector. This injection pressure is greater than actuation pressure by approximately six times. The pressure in the system is multiplied by the intensifier piston that is located in the injector.Low actuation pressure results in low injection pressures. During conditions of low engine speed such as idle and start, the low injection pressure is due to the low actuation pressure that is being produced by the unit injector hydraulic pump.High actuation pressure results in high injection pressures. During conditions of high speed such as high idle and acceleration, high injection pressures can be produced because of the high actuation pressures that are produced by the hydraulic pump.There are many other operating conditions when the injection pressure fluctuates between the minimum and the maximum. Regardless of the speed of the engine, the HEUI fuel system provides infinite control in order to provide the optimum fuel injection pressure.Electronic Control Module (ECM)
The Electronic Control Module (ECM) (30) is mounted directly on the engine. The ECM is a powerful computer that provides total electronic control of engine performance. The ECM gathers performance data from the engine through a series of engine sensors. This data is used by the ECM in order to modify the engine's fuel delivery, injection pressure, and injection timing. The ECM also contains performance maps in the form of software that define engine's horsepower, torque curves, and rpm.Most of today's engines are equipped with an ECM that can be reprogrammed in the field. There are electronic service tools that can be used to program the ECM. These electronic service tools use flash programming in order to load new software into the ECM.The ECM is also used to record engine faults that may occur. These faults are usually triggered when one of the engine sensors detect a parameter that is operating out of the normal range of operation. An electronic service tool can be used in conjunction with the engine ECM to run several diagnostic tests on engine's electrical systems or electronic systems.Unit Injector Hydraulic Pump
The unit injector hydraulic pump (1) is a high pressure hydraulic pump that is located at the front of the engine. The unit injector hydraulic pump is a variable displacement axial piston pump that is driven by the front gear train of the engine. The unit injector hydraulic pump uses a portion of the engine lubrication oil to supply the HEUI fuel system. The unit injector hydraulic pump pressurizes the engine lubrication oil to the correct injection actuation pressure in order to power the HEUI injectors.Injection