How Does An HEUI Pump Work?

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In 1994 Caterpillar partnered with International to build a fuel injection system for all power stroke engines. The HEUI injection system was the result of that collaboration.

A type of unit injection system that uses hydraulics to pressurize the fuel. This enabled the HEUI to create higher fuel pressure (21,000 -26,000 psi), which results in richer combustion. To build the fuel pressure, the system uses something known as the HEUI pump.

heui high pressure oil pump 10r8899 for caterpillar c7 2

What is an HEUI pump? Why do we need it?

The HEUI stands for Hydraulic actuated electronically controlled unit injection. As the name sounds, the HEUI is a unit injection system that uses hydraulics for building fuel pressure. But while the hydraulics is electronically operated, it is powered by high oil pressure.

This pressurized oil is transferred by a High-Pressure Oil Pump (HPOP) connected to the HEUI system, hence the name HEUI pump. The HEUI pump pressurizes the engine oil which is fed to the HEUI injector. The high-pressure oil then pushes the plunger which then pushes the fuel and pressure is created.

To generate the required pressure, the PCM controls the IPR (injection pressure regulator). The IPR then regulates the pressure as per engine requirements. In general, a 7.3L power stroke engine needs around 450 – 3000 psi while the 6.0 needs 450 – 3600 psi of oil pressure.

How does an HEUI pump work?

The working of the HEUI pump is pretty simple and direct. First, the oil from the engine is delivered to the high-pressure oil pump through the engine oil pump. The HPOP then pressurizes the oil. The pressure of the oil is dependent on the engine load that is calculated by the PCM.

The range of oil pressure as mentioned is between 450-3600 psi. Again the IPR which is in control of the oil pump outlet’s pressure limits the oil pressure to the required amount.  The HPOP then transfers the pressurized oil to the cylinder heads where barrels (oil passage) are located.

From the passage, the oil now reaches the HEUI injectors. The injectors have oil chambers that are closed by solenoids. At the same time, the fuel is also transferred to the injectors via the fuel pump. A cam sensor located above harmonic dampers senses when the injector is ready and notifies the PCM.
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The PCM then sends the signal to the injectors driving module to “fire”. As the signal is received by the IDM, the solenoid then releases the poppet valve which then opens to let the high-pressure oil in.  The oil is then filled in the cavity on the intensifier (piston) inside the injector.

The intensifier is pushed down due to oil pressure, which then pressurizes the fuel. The amount of pressure put on the fuel is dependent on oil pressure and the cross-section area of the intensifier pushing the fuel down.

Since a 7.3 L engine has a 7:1 ratio of the cross-section area of the top of the plunger and the bottom. The force applied by the oil is multiplied by 7 times. Meaning on max output, the fuel can be pressurized to 21,000 psi by the HEUI pump in the 7.3 L power stroke engines.

Once the fuel is pressurized, the injector nozzle is then opened to let the fuel in the combustion chamber for combustion. The high fuel pressure helps the fuel atomize which makes combustion incredibly easier and efficient.

How do I know if my Heui pump is bad?

The HEUI is a fuel pump. A failure of such a pump immediately means no/reduced engine output. So, if you drive a machine with an HEUI pump, here are a few things you can watch out for.

No ignition: In an event of failed HEUI, the engine would seize to start. This can be because of low fuel pressure. It can be caused if the injector is left open or due to an oil leak. If there is not enough pressure, the injection nozzle would not open and no fuel would get atomized.

Lack of power:  There can be a significant lack of performance if the HEUI injector fails. It can happen if the HPOP(high-pressure oil pump) fails to deliver the required pressure. Or if the solenoid gets faulty. In both conditions the lack of fuel pressure would result in bad combustion, restricting the engine output.

You can have low oil pressure due to missed out oil changes or by using a different kind of oil than suggested. 

Wear: Over time, the HEUI pump also gets worn due to ultra-low sulfur diesel. It can cause small leaks of high-pressure oil affecting the whole system.

In any case, a faulty HEUI pump needs immediate repair and replacement. Not doing so would put unwanted stress on your engine. Which in no way is healthy for your machine. 

By the way, if you want to know about HEUI Injectors, please visit our another blog post: All you need to know about HEUI Injectors

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