All you need to know about HEUI Injectors

The HEUI Injectors were first introduced in 1994 by Caterpillar. Mainly used in the Power Stroke diesel engines, these injectors enabled them to produce more power and torque with better fuel efficiency and cleaner emission.

Over the years, the HEUI injector has been used in multiple CAT vehicles including the C7 and C9 along with Ford and GM pick-up trucks. So, what makes this injector so important?

In this article, we will discuss HEUI injector, their application, How do HEUI injectors work, and HEUI faults and symptoms.

What is an HEUI Injector?

The term HEUI stands for Hydraulic actuated, electronically controlled Unit Injector. In simple words, it is a unit injector system that works using the principle of hydraulics.

A unit injector is a combination of injector nozzle and injection pump. Developed by Bosch, these are electronically controlled high-pressure direct fuel injection systems used in diesel engines. When hydraulic was added as a way to pressurize fuel with the ability to be controlled by ECM, it became the HEUI system.

Since delivering fuel at a higher pressure improves the vapourization, it results in richer and cleaner combustion. For diesel companies that were haunted by the emission regulations in the 90s, a system like this was a miracle.

With ECM integration the process could now be controlled more precisely resulting in high fuel efficiency. It was all the immediate benefits of the HEUI injector that made it a revolutionary invention of the time.  

How do HEUI Injectors work?

Principal: The HEUI Injector works on a very basic principle of pressure. Since Force/ Area = Pressure, the higher the force is applied in the lower amount of area, the more pressure it will create. The HEUI injector is integrated with the HEUI pump which pumps the pressurized engine oil to put pressure on the fuel.  

Working: The initial job of the HEUI pump is to pressurize the fuel for injection. To do so, the HEUI uses a simple piston referred to as an intensifier. The intensifier is first pushed by pressurized engine oil which then pushes the fuel. The pressure put on the fuel is decided by the cross-section area.

In a 1:1 system, the pressure of the fuel is equal to the pressure applied on the intensifier. To increase the pressure, the area is reduced. So, in the 2:1 system, the pressure on the fuel is double the pressure on the intensifier. Because the exit of the fuel is reduced by half, as in the image below.

In 7.3L power stroke engines, the fuel pressure is 7 times the intensifier pressure, a 7:1 ratio. Again to do so, the cross-section area of the nozzle from which the fuel exits is 7 times smaller than the area on which oil pressure is applied.

Working of HEUI injection in the engine:

The HEUI injector’s job is to inject fuel at high pressure when the PCM/ECM commands it. The PCM does so by sending signals to the IDM (Injector Driving Module) or FICM (Fuel injection control module). The IDM controls the solenoid by controlling the voltage.

Depending on the voltage, the solenoid releases the force on the poppet valve. Since the poppet valve is counter-pushed by springs, as the solenoid releases it, it is pushed up by the springs. This opens a pathway for the pressurized oil to fill in the cavity. This pressure is decided on engine load rather than engine speed.

The pressurized oil then pushed the intensifier piston. The piston in return pushes the fuel in the cavity located at the injector’s nozzle. Again the injector nozzle valve is kept closed using the spring action.

Only when the fuel reaches a preset pressure does it overcome the spring force and exit the nozzle. Since the nozzle exit is incredibly small, the high-pressure fuel going out of an even smaller area gets atomized. The atomized fuel enters the combustion chamber and combustion happens.   

Benefits of HEUI Injection System:

The HEUI Injectors have some very obvious benefits. Since they are electronically controlled injection systems, the injection can be controlled depending on various events. Unlike mechanical injection, HEUI injection is not limited to preset parameters. As they are not in any way dependent on the camshaft.

The HEUI system is also able to put out more pressure. In the 7.3L power stroke engine, it can put out 21,000 psi while the 6.0 power stroke has 26,000 psi of fuel pressure. The higher the pressure, the better atomization can happen. Ultimately resulting in richer combustion.

Thanks to the higher combustion quality, engines with HEUI injection had better fuel efficiency with lower combustion. Along with a significant boost in power production.

What engines use HEUI injectors?

The HEUI injection was introduced in 1994 where it was first used in the 7.3L/444 V8 diesel engine from Navistar. Between 1993-2007, Ford’s 7.3L and 6.0L Power stroke featured the HEUI injectors.

Other manufacturers like International used the HEUI tech for their DT466E, DT570, T-44E, DT-466-570,  with the MaxxForce 5,7,9,10, and DT. The HEUI system was also used in CAT 31116, 3126, 3406e, C7, and C9 ACERT. Later the system was replaced by CRDI tech.

Differences between HEUI injectors and non-HEUI?

The list of non-HEUI injectors includes the modern-day CRDI system along with the old mechanical injection system.

The mechanical injection was a two-phase system that first built pressure using the fuel pump and then fed injectors of each cylinder. It was the pressure of the fuel that opened the injector check valve to spray fuel. While this was a consistent way of delivering fuel, it wasn’t flexible enough to adjust as per engine load.

The HEUI injection was an electronically controlled system that not only provided higher pressure. But also provided better accuracy with injector timing and fuel metering. Since the system was controlled by a computer, adjustments were made quickly depending on engine load. While the HEUI engines were way better than Mechanical Injectors. The Common Rail Direct Injection System proved to be even better.

With a dedicated and regulated high-pressure fuel pump, required pressure is constantly maintained inside a common rail. The Rail feeds the fuel to all the injectors at once, or in stages.

What made the CRDI different is its ability to inject fuel multiple times in one combustion cycle. The improved accuracy boosted everything from efficiency to power production. Which was the real reason the HEUI was phased out by CRDI. 

By the way, if you want to know about HEUI Pump, please visit our another blog post: How Does An HEUI Pump Work?