Common Rail Pressure Relief Valve Symptoms and Fixes

There are many types of engines that are used to power different types of machines. Heavy equipment and generators can be equipped with a common rail system for fuel distribution across the various fuel injectors. The common rail pressure relief valve, one of the components in these systems, can malfunction, leading to serious problems.

In our article today, we take a keen interest in understanding the common rail pressure relief valve. The valve also carries the CRPRV acronym. We look at why it malfunctions and the symptoms to look out for when it does. We further explore how one can fix the valve and return your equipment to its normal operating state.

Understanding common rail system

In a conventional engine, fuel comes directly from the fuel tank to each injector. In the common rail system, the fuel, diesel, is pumped from the engine and onto a common rail where each injector draws the fuel it requires. The common rail will store the fuel and supply the injectors per the demand. Common rail pressure relief valves are installed in small and heavy-duty vehicles. You will also find this system being used on;

• equipment and heavy engines
• ship engines
• generators
• factory machines.
• Agricultural equipment
• Construction Equipment

The fuel flow is electronically controlled by the ECM (electronic control module) and stored at variable pressure inside the common rail. Once the fuel is drawn from the fuel tank, its flow and pressure are controlled by the fuel pump. However, the fuel pump and the injectors control the timing of fuel injection as well as the amount of fuel injected.

When the high-pressure pump pumps the fuel, it enters the common rail but not before it passes by the fuel filter, where impurities are sieved off. Once fuel enters the common rail, the common rail sensor detects the pressure inside the rail. The pressure common rail valve opens or closes to allow fuel flow out or in depending on the pressure required in the rail. The excess fuel released by the pressure valve returns to the fuel tank via the return system.

Understanding the common rail pressure relief valve

The engines that employ this technology are so designed, bearing in mind the need to satisfy the strict pollution regulations and standards. To make the common rail system work efficiently, the pressure inside it is controlled electronically. This allows the engine to perform optimally, whether in power delivery, fuel consumption or emission of cleaner exhaust gases.

In the common rail pressure system, the fuel is stored in the rail and is available at the right pressure whenever an injector needs it. The pressure valve is mandated to ensure that the pressure in the rail is always in accordance with the varying injector demands.

If the pressure exceeds the required level, the valve will open and dispose of excess fuel back into the fuel system. If the pressure is below the required level, the valve remains closed, and the pressure builds up to the required level. The pressure in the common rail will vary within a given range depending on the engine load the speed. The pressure usually varies between 23,000 and 29,000 PSI.

As mentioned earlier, the pressure valve is regulated electronically depending on the needs of the injectors. Several things and components fail to perform as required if the valve malfunctions. In some instances, the engine might stall, fail to start, or the fuel efficiency deteriorate exponentially.

What are the symptoms of a faulty common rail pressure relief valve?

1. Error codes - The ECM will record the relevant error codes when the common rail pressure relief valve malfunctions. The ECM will send a warning light to the machine's display to warn you of the problem at hand. When you use the error code scanner, you may read several error codes depending on the machine or equipment you are diagnosing. Among the codes you may find include; 523470, 523009, 3104 or 3173.
2. Deteriorating fuel efficiency - This may arise when more than the required fuel is fed to the injectors. The injector in this system does not control the pressure of the fuel to determine the fuel-air mixture. If excess fuel is in the rail, the injector will likely inject excess fuel into the combustion chamber.
3. Excessive smoke - When your machine or equipment loses the benefit of the CRPV, you will likely witness excessive smoke coming from the exhaust. This may be due to the excessive fuel supplied to the injectors, which end up in the combustion chamber.
4. Reduction in power - Unlike conventional fuel systems, the common rail system is very efficient and reliable. Each injector is supplied with just the right amount of fuel every time. A faulty CRPV makes the fuel pressure to be unregulated, which then makes the injectors supply non-optimal fuel to the cylinder. This will then cause the performance of the engine to drop. This will be especially the case when the machine is under load.
5. No starts or hard starts - Hard starts and failure of the engine to start will be common because of the interference with the fuel system caused by a malfunctioning CRPV.

How to check whether the common rail pressure relief valve is faulty

The one thing that you must be aware of is that if the aforementioned valve malfunction is neglected, more severe problems may arise. When the valve relieves pressure from the common rail, it gives a 'count' to the ECM. These counts accumulate until they give a fault code, and it's then it starts derating.

If you suspect the common rail pressure relief valve is malfunctioning, the first thing to check is the ECM to see whether the valve has logged any counts. If there are any counts, you should first establish why this has happened. The leading causes of the CPRV log count on ECM include;

• Faulty metering units
• A fault with the pressure valve
• Blocked fuel return lines
• Fuel pressure sensor
• The high-pressure pump
• Maintenance neglect
• ECM is not getting adequate power
• A mechanical fault in the fuel system or the engine
• A wiring problem

To get to the root cause of a malfunctioning common rail pressure relief valve fault, you should conduct tests to help you come up with the correct diagnosis. A professional should handle this fuel system component. The mechanic has the proper tools and skills to help them carry out the proper tests, after which they will correct the problem.

This does not mean that you cannot do your own physical observation and correctly conclude that the valve is the one with the issue. But because of the specific nature of the work the valve does, it is recommended that you seek the services of a qualified professional.

Solution to a faulty rail pressure relief valve

The solution to a faulty CRPRV is a replacement. There is no recommended trick that one can apply to repair this valve. Moreover, the valve performs a critical function, and once it malfunctions, trying to repair it might be counterproductive.

For the majority of farming machinery, the CRPRV is accessible and working on it or around it is not tedious. Replacing the valve should be quick and relatively cheap. The valve is available in most brick-and-mortar stores and online stores.

The CRPRV specifics change according to the requirements of the particular engine needs. Even though two generators carry the same manufacturer's logo, the horsepower and other specifications vary from one variant to the next. This then means the valve should be calibrated accordingly. The user manual of the machinery will usually indicate the specific PSI range the valve should be set at. It is for this reason that an expert is required to replace the valve.

Failure to service your equipment or machinery can cause fuel system problems. You should replace the fuel filter as recommended and carry out other maintenance functions as the user manual specifies. You are more likely to experience CRPRV issues if you neglect to service the machinery regularly. Moreover, it will be easier to pinpoint and diagnose the issue on an engine that is regularly serviced, unlike one that is neglected, which has a plethora of issues.

Conclusion

The common rail pressure relief valve for heavy machinery, whether in a farming setup or in construction performs a critical role in ensuring the fuel reaches the combustion chamber as intended. In our article, we have taken a closer look at how this valve works and the likely symptoms it might exhibit when it malfunctions.

As pointed out earlier, the symptoms exhibited by a faulty CRPRV can sometimes be generic and confused with those of other components. Therefore, it is important to use a diagnostic machine to help you locate the specific source of the problem. It is further important that the services of an expert in the field be sought to ensure that the valve is torqued as per the machine's requirements.