C7 Industrial Engines Systems Operation – Fuel System


Illustration 1 g01447542
Fuel System Diagram

(1) Unit injector hydraulic pump

(2) Oil flow to engine

(3) Oil filter

(4) Engine oil pump

(5) Injectors

(6) Connector for the IAP control valve

(7) Oil cooler

(8) High pressure oil passage

(9) IAP sensor

(10) Fuel supply passage

(11) Fuel transfer pump

(12) Secondary fuel filter

(13) Primary fuel filter/water separator

(14) Fuel tank

(15) Fuel pressure regulator

(16) Back of camshaft gear

(17) Speed/timing sensors

(18) ECM

(19) Boost pressure sensor

(20) Engine coolant temperature sensor

(21) Engine oil pressure sensor

(22) Inlet air temperature sensor

(23) Engine oil level switch

(24) Atmospheric air pressure sensor

(25) Wastegate control valve

The 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 Electronic Control Module (ECM) (18) .

This fuel system consists of six basic components:


  • Hydraulic Electronic Unit Injector (HEUI) (5)
  • Electronic Control Module (ECM) (18)
  • Unit injector hydraulic pump (1)
  • Fuel transfer pump (11)
  • Injection Actuation Pressure sensor (9)

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 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 28 MPa (4050 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.

Electronic Control Module (ECM)

Electronic Control Module (ECM) (18) 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.

The engine does not have a replaceable personality module. The personality module is a permanent part of the ECM. The personality module for the engine can be reprogrammed by Caterpillar Electronic Technician (Cat ET).

ECM (18) 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 or the Electronic Control Analyzer Programmer (ECAP).

Unit Injector Hydraulic Pump

Illustration 2 g01447556
(1) 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 variable delivery piston pump. 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.

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