The Sensitivities of High-Pressure Common Rail Fuel Systems

By December 17, 2018Older Posts, News

By Keith Kramlich, National Service & Warranty Manager at Takeuchi


It is becoming an all-too-common trend: operators putting contaminated fuel into their machines, which is in turn destroying the fuel system.

High-pressure common rail fuel systems (HPCR) are now standard on nearly every diesel engine today from heavy equipment to over-the-road trucks, light-duty trucks, cargo vans, large generators and more. HPCR fuel systems have many advantages, but the system has also caused confusion amongst operators.

To ensure the engine keeps humming for hours to come, it’s important to understand the fuel system itself, the advantages and disadvantages, the sensitivities of the system, the impact contaminated fuel has, and warning signs to look for.

Understanding HPCR Fuel Systems

For starters, it’s always good for operators to know what they’re working with. In 2004, the EPA implemented the Tier IV Emission standards and mandated the standards be phased in between 2008 to 2015. In 2012, Takeuchi began the implementation of Tier IV engines in select equipment. Tier IV is now standard across all models.

The only exception is that lower-horsepower machines are still able to utilize mechanical injection systems in order to meet emissions standards set for the displacement of the engine utilized.

The newer system consists of a high-pressure fuel rail common to all the injectors. Fuel is supplied to the high-pressure fuel rail by a high-pressure supply pump. Depending on RPM and engine load, the pressure in the rail can exceed 30,000 to 40,000 PSI. The injectors are electronically controlled, and each has its own firing mechanism or solenoid.

Advantages and Disadvantages

Engines equipped with HPCR provide cleaner exhaust, have more horsepower, and are more efficient than previous models. Because of the design, HPCR systems also deliver better atomization of the fuel upon injection, delivering a cleaner, more powerful and more complete combustion.

Some would say the main HPCR system drawback is the complexity behind the electrical components. There are numerous sensors, wiring harnesses and electrical components that need to be added to ensure the engine performs as it should. Another perceived negative is how sensitive these units are.

Vulnerable Systems

Before Tier IV emissions requirements, non-road diesel engines utilized a mechanical injection system. These systems were not as sensitive to contaminated fuel. Because of this, many operators are under the misconception HPCR fuel systems can as well. In reality, this could not be further from the truth.

Diesel engines have progressed, so there are new recommendations to follow. Dirty or incorrect fuel, water in the fuel, and air in the system can all cause damage to newer diesel models.

These systems are highly susceptible to damage if proper care is not followed. This is because common rail fuel systems operate under such high pressure and have precise components with fine tolerances, making them extremely vulnerable. So, while a certain amount of contamination or water will not cause harm to the older design mechanical injector, the same fuel will wreak havoc on a common rail fuel system.

The Impact of Contaminated Fuel

The most common culprit when it comes to damage is water in the fuel, which often comes from unmaintained transfer tanks. These tanks have a few issues:

  • In some cases, they rarely get drained.
  • Water accumulates in the tank from condensation.
  • Due to the location of these tanks and the environment the service trucks are in, they can collect heavy debris. Therefore, it’s important to clean the fuel cap and surrounding area before filling the transfer tank.
  • If the tank is not maintained, the water content will continue to increase and could lead to rust inside the tank and lines.

To help with this issue, Takeuchi machines come equipped with a fuel and water separator, but it’s not a complete solution on its own. It needs to be checked and drained daily. If it isn’t and the water level reaches the top of the separator, water will be forced through the separator and back into the fuel system, reaching vital components.

Water in the fuel can impact several different aspects of the machine:

  • Most often, it will decrease the lubricity of the fuel. This causes damage to the needle valve inside the injector, which will become sticky and result in high return flow or high fuel delivery.
  • The needle valve can also be damaged to the point it no longer seals properly, allowing the injector tip to leak.
  • Metal from the needle valve damage or from other component damage can clog the nozzles, resulting in a distorted spray pattern. This will result in fuel being sprayed directly onto the piston surface or the cylinder wall.
  • Fuel directly injected into the cylinder wall will cause cylinder wash, which is when the fuel washes the lubricant oil away. The result is poor lubrication between the piston and cylinder wall, causing wear. This inevitably leads to low compression, oil dilution and engine failure.
  • In some cases, free water can be pushed into the injector. Excessive heat in the injector will cause this water to turn into steam and expand, triggering a failure in the injector tip.
  • Excessive heat in the injector will cause the water to turn into steam and expand, triggering a failure in the injector tip.
  • Damage to the needle valve can prevent it from sealing properly when shut. This allows non-atomized fuel to leak onto the piston surface, resulting in a melted piston.
  • Other contaminates, such as dust particles and low-quality diesel fuel with low lubricity properties, will damage the fuel system as well.

For all these reasons, it’s critical to maintain a clean fuel system and frequently change fuel filters. Every Takeuchi machine has one to two fuel filters and a water separator. The fuel system on Takeuchi machines is very effective at removing harmful contaminants and water from the fuel system. However, fuel filters cannot filter fuel contaminants if the filters are not serviced regularly.

Ensuring that clean fuel is being used is the simplest and most important thing to do. This includes using a trusted source that has clean and filtered fuel. When filling, it’s also necessary to have the fill neck screen in place to prevent large debris from entering the tank. Large debris can restrict the fuel flow from the tank or, depending on the material, it can break down and become small enough to cause fuel system issues.

Warning Signs

Most commonly, the first sign of engine failure from fuel contamination is multiple failed injectors. Though these are the same components, they operate separately and only have one thing in common: the fuel source.

If an operator starts to notice poor engine performance, excessive smoke, unnecessary regeneration requests or anything else abnormal, it is best to stop the engine before catastrophic damage occurs.

The last thing a machine owner or operator wants is downtime because of failure. Some things are easily fixed, but an engine is not — a failed engine will cost a lot more than just a minor work interruption. Using clean and filtered fuel of the best quality is paramount and will save the owner thousands in repair costs along the way.