What is the EGR valve for?
Today, for the workshop, we take a popular and hateful EGR valve, which often causes serious problems with the engine’s operation. Are you sure you need it, what it is for, how it works, why it breaks down and what are the symptoms of its failure? I will try to answer these questions today.
At the beginning, it is worth developing the popular EGR abbreviation, which stands for Exhaust Gas Recirculation, which is a simple translation of the exhaust gas recirculation system. This is important because not only the EGR valve, which is commonly known, is part of it. In some engines, the system of variable valve timing is also part of the EGR system. This is called internal implementation of exhaust gas recirculation, consisting in the earlier opening of the exhaust valve, which in effect results in the return of some of the exhaust gases to the intake system. The external way of implementing Exhaust Gas Recirculation is the use of the EGR valve, which is popular and discussed in this article.
What is the EGR valve for?
The purpose of using the EGR valve is to reduce the amount of oxygen supplied to the combustion chamber and thereby reduce the temperature and slow down the combustion process and reduce the emission of nitrogen oxides (NOx). The effect of reducing the amount of oxygen in the combustion chamber is accomplished by adding to the intake system an appropriate portion of the exhaust gas, which in a simplified way contaminates the air supplied to the chamber.
How does the EGR valve work?
In engines equipped with an EGR valve, the exhaust and intake system connects a relatively narrow conduit that allows a small portion of exhaust to flow into the intake manifold. The EGR valve is an element of this duct, deciding on whether the flue gas will hit the intake and when it will happen. The first EGR valves were pneumatically controlled and did not smoothly regulate the exhaust gas entering the intake – they simply opened or closed. Newer devices with electromagnetic control open smoothly, in any range, precisely adjusting the portion of flue that is to be buried in the combustion chamber at a given moment.
The EGR valve opens only under certain conditions, today the engine control unit decides about it. The EGR remains closed at idle speed and until the engine is loaded and / or reaches the optimum operating temperature. It does not open even at full engine load. Most often, a portion of the exhaust gas returns to the engine at low and medium load, especially in the middle rpm range.
In newer engines that meet the Euro 4 standard, EGR coolers are used, whose task is to cool exhaust gases that later go to the valve. This topic I will deal with in a separate article.
What are the negative effects of using an EGR valve?
The main negative effect of using the EGR valve is to lower the engine power, but it is worth noting that this is not directly related to the maximum power value, because at full load the EGR valve remains closed. However, indirectly it affects the power indirectly, because the action of EGR in the long-term causes contamination of the inlet manifold with a cold, which reduces the cross-section of its channels.
Why the EGR valve breaks down?
The most frequent cause of EGR valve failure is its pollution, although in more recent solutions damage to the control systems is getting worse. Large pollution causes difficult operation of control elements, their overloading and, as a result, failure. The high risk is also related to the aggressive action of exhaust gases on the EGR valve elements, so it is not uncommon to burn the material inside the valve.
Symptoms of problems with the EGR valve
Symptoms of EGR damage may vary depending on the type of failure. As there is usually strong pollution and problems with the flow of exhaust gas to the intake system, usually a message appears in the form of a check engine indicator on the instrument panel. There are also problems with obtaining the full engine power, because the clogging of the EGR valve is certainly associated with strong intake manifold contamination. If the EGR valve locks in the closed position, the exhaust system usually appears to be on track and errors in this area are recorded in the computer. In addition, the driver will not feel anything that can directly affect the operation of the engine.
Most often, however, the valve locks in the open position, and this is associated with strongly perceptible symptoms, such as uneven idle engine operation, difficulties with smooth acceleration and difficult start of the cold engine.
If not an EGR valve is what?
It is not uncommon for other engine control parts to malfunction and the EGR valve is suspected. Sometimes and vice versa, where EGR valves are to blame for problems, and incorrect diagnosis may lead to unnecessary replacement of other elements. A perfect example of the first situation is the failure of the air temperature sensor in the flowmeter, the information provided to the computer controlling the operation of the engine affects the control of the EGR valve as well. A defective flow meter will also cause EGR disruption. On the other hand, it works in such a way that, for example, leakage of the EGR valve or blocking it may indicate a flowmeter failure. Its hasty replacement can be expensive and will certainly not be effective. There is also damage to vacuum pipes (attention to rodents) that control valve operation. There are also disruptions in the operation of the solenoid valve position sensor itself or the vacuum valve. If only these elements can be replaced, it will not be necessary to replace the entire valve.
When diagnosing and attempting to repair, it is absolutely necessary to determine the true cause of the problems and check the efficiency of the EGR valve.
Cleaning or replacing the EGR valve?
Unfortunately, most often failures are noticed and recognized quite late, which in effect means a failure indicating the need to replace the EGR valve. Cleaning itself helps in older, simple constructions. Practice shows that cleaning a modern EGR valve has no effect or is short-lived. What’s more, when deciding to clean the valve it is also worth cleaning the intake manifold. It is good practice to prophylactically clean the valve every 60-80 thousand. km. It will certainly prolong its durability, but it will not give 100% confidence in its trouble-free operation for the next such course.
Much better than cleaning the valve itself is replacing it with a new one. However, it involves considerable costs. Unfortunately, this does not always solve all problems for a simple reason – poor quality replacements. Not everyone can afford the original part, which often costs from a thousand to several thousand zlotys. Substitutes are cheaper, and regenerated valves are even cheaper. It must be remembered that a regenerated valve or any other part has a factory quality and durability only when the worn parts have been replaced with new ones, original ones and when the manufacturer has foreseen a technological possibility of replacing them. Otherwise, the purchase of a regenerated valve may turn out to be a financially bad decision. There are companies on the market that offer valves, which in reality have only been thoroughly cleaned and painted.