Component Description

TM 9-2320-312-24-2

Systems Operation Section

(27) Inlet air heater lamp

(14) Speed/timing sensors

(1) Unit injector hydraulic pump

(28) Fast idle lamp

(15) ECM

(2) Oil flow to engine

(29) Check engine lamp

(16) Boost pressure sensor

(3) Oil filter

(30) Speedometer and tachometer

(17) Accelerator pedal

(4) Engine oil pump

(31) Cruise ON/OFF switch and Cruise

(18) Accelerator pedal position sensor

(5) Oil cooler

SET/RESUME switch

(19) Batteries

(6) IAP sensor

(32) PTO ON/OFF switch and SET/RESUME

(20) Coolant temperature sensor

(7) Injectors

switch

(21) Data link

(8) Fuel supply rail

(33) Service brake switches

(22) Exhaust brake relay

(9) Fuel pressure regulator

(34) Neutral and clutch switches

(23) Inlet air temperature sensor

(10) IAP control valve

(35) Fuel transfer pump

(24) Transmission relay

(11) Fuel filter

(25) Vehicle speed sensor

(12) Fuel tank

(26) Inlet air heater relay

(13) Back of cam gear

The HEUI uses engine lubrication oil that is

The operation of the Hydraulic Electronic Unit

pressurized from 6 MPa (870 psi) to 27.5 MPa

Injector (HEUI) fuel system is completely different

(4000 psi) in order to pump fuel from the injector.

from any other type of fuel system that is actuated

The HEUI operates in the same way as a hydraulic

mechanically. The HEUI fuel system is completely

cylinder in order to multiply the force of the high

free of adjustment. Adjustments to the components

pressure oil. By multiplying the force of the high

that are mechanical can not be made. Changes

pressure oil, the HEUI can produce injection

in performance are made by installing different

pressures that are very high. This multiplication of

software in Engine Control Module (ECM) (15).

pressure is achieved by applying the force of the

high pressure oil to a piston. The piston is larger

This fuel system consists of six basic components:

than the plunger by approximately six times. The

Hydraulic Electronic Unit Injector (HEUI) (7)

piston that is powered by engine lubrication oil

under high pressure pushes on the plunger. This

Engine Control Module (ECM) (15)

engine lubrication oil under high pressure is called

the actuation pressure of the oil. The actuation

Unit injector hydraulic pump (1)

pressure of the oil generates the injection pressure

that is delivered by the unit injector. Injection

Injection Actuation Pressure Control Valve (10)

pressure is greater than actuation pressure of the

oil by approximately six times.

Fuel Transfer Pump (35)

Low actuation pressure of the oil results in low

Injection Actuation Pressure Sensor (6)

injection pressure of the fuel. During conditions

of low speed such as idle and start, low injection

pressure is utilized.

Note: The components of the HEUI fuel system are

not serviceable. These fuel system components

High actuation pressure of the oil results in high

must not be disassembled. Disassembly will

injection pressure of the fuel. During conditions of

damage the components. If the components have

high speed such as high idle and acceleration, high

been disassembled, Caterpillar may not allow

injection pressure is utilized.

a warranty claim or Caterpillar may reduce the

warranty claim.

There are many other operating conditions when the

injection pressure is between the minimum and the

Component Description

maximum. Regardless of the speed of the engine,

the HEUI fuel system provides infinite control of

Hydraulic Electronic Unit Injector

injection pressure.

The HEUI fuel system utilizes a hydraulically

Engine Control Module (ECM)

actuated electronically controlled unit injector (7).

Engine Control Module (ECM) (15) is located on

All fuel systems for diesel engines use a plunger

the left side of the engine. The ECM is a powerful

and barrel in order to pump fuel under high pressure

computer that provides total electronic control of

into the combustion chamber. This fuel is pumped

engine performance. The ECM uses data from

into the combustion chamber in precise amounts in

engine performance that is gathered by several

order to control engine performance. The HEUI uses

sensors. Then, the ECM uses this data in order

engine oil under high pressure in order to power the

to make adjustments to the fuel delivery, injection

plunger. All other fuel systems use a fuel injection

pressure and injection timing. The ECM contains

pump camshaft lobe in order to power the plunger.

programmed performance maps (software) in order

Because the HEUI is much different, a technician

to define horsepower, torque curves and rpm. This

must use different troubleshooting methods.

software is commonly called the personality module.