28 Successful Farming at Agriculture.com |August 2019 Photography: Bosch
m a c h i n e r y INSIDER™ Continued
HEUI HANGOVERS
IDENTIFYING THE WEAKNESSES OF HYDRAULIC
ELECTRONIC UNIT INJECTOR SYSTEMS.
T
he first GMO crop
introduced into the
American market
was the Flavr Savr
self-ripening tomato
in 1994, the same year that
the hydraulic (activated)
electronic (controlled) unit
injector, or HEUI for short
(pronounced Huey), was
first seen on a diesel engine.
The controversy about and
misunderstanding over both
technologies rage on today.
The HEUI system was
more than just a new
injector theory; it was the
offspring of a joint effort
between Caterpillar and
By Ray Bohacz
International Trucks that
began in 1987. A new
method to fuel a diesel
engine was required with
the upcoming emissions
control standards.
The HEUI system was
common in International
466E and 530E engines,
mainly found in medium-
duty trucks and school
buses, and the Cat 3126,
among other applications.
HEUI gained its notori-
ety under the hood of the
first Ford Power Stroke en-
gines. The HEUI family of
fuel delivery was employed
on many agricultural
engines produced by Cat,
as the company temporarily
moved into farm machin-
ery production.
The Cat C-7 and C-9
engines, often fitted to
Challenger tractors and
other farm uses with the
ACERT system, enjoyed
the application of the
HEUI design.
Whereas an electronic
unit injector (EUI) em-
ployed a camshaft profile
to operate it, the HEUI
uses engine oil at very high
pressure (4,000 psi) instead.
This was the first time
the fuel pressure and injec-
tor opening timing could
be varied independently.
It allowed for the fuel
delivery curve to be infi-
nitely shaped. In addition,
it meant less wear on the
camshaft and no cam pro-
file limit to fuel delivery.
In simple terms, the
HEUI employed a swash
plate oil pump design that
replaced camshaft actua-
tion. Due to the combina-
tion of the high engine oil
pressure on one side of the
injector, the HEUI system
can enjoy nozzle open pres-
sures of as high as 5,000
psi with a potential peak
pressure of 28,000 psi.
The oil pressure acting
on the HEUI amplifier
piston is multiplied seven
times in the fuel pump
chamber.
The blending of the
hydraulic and electronic
controls along with precise
electronic discharge ma-
chining, raised fuel atomi-
zation to a new standard.
HEUI weaknesses
I
n engineering, we use the
acronym KISS: Keep it
simple, stupid! The only
problem is that advanced
control of the fuel events
cannot be achieved with
the simplicity of a mechani-
cal injector.
Complexity is a necessary
evil of the HEUI system,
but it is a very reliable injec-
tor once its Achilles’ heels
are identified. For starters,
HEUI engines are noisier
since there is no pilot injec-
tion pulse and, instead, uses
one injection event.
Due to the high pres-
sure (500 to 3,600 psi), the
oil is exposed to and then
sent back into the oil pan to
lubricate the rest of the en-
gine. The result is that it has
a reduced service life and
is prone to chemical and
viscosity breakdown. In ad-
dition, a very high-quality
oil of the proper grade and
specifications must be used,
Complexity is
a necessary
evil of the
HEUI system,
but it is a
very reliable
injector once
its Achilles’
heels are
identified.
