User Manual

Introduction
The operation of the Hydraulic Electronic Unit Injector fuel system is completely different from any other 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 the ECM.
This fuel system consists of four basic components:
• Hydraulic Electronic Unit Injector (HEUI)
• ECM
• Unit injector hydraulic pump
• Fuel transfer pump
Note: The fuel transfer pump is a serviceable part. The internal 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 fuel system utilizes a hydraulically
actuated electronically controlled unit
injector.
All fuel systems for diesel engines use a
plunger and barrel in order to pump fuel
under high pressure into the combustion
chamber. The HEUI uses engine oil under
high pressure in order to power the plunger.
The HEUI uses engine lubrication oil that is
pressurized from 6 MPa (870 psi) to 28
MPa (4061 psi) in order to pump fuel from
the injector. The high pressure oil is called
the injection actuation pressure. The HEUI
operates in the same way as a hydraulic
cylinder in order to multiply the force of the
high pressure oil. 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. 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. High actuation pressure of the oil
results in high injection pressure of the fuel.