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An Exhaust Gas Recirculation valve is one of the most important emissions-controls in your car, although it’s seldom mentioned outside of the automotive industry.
Almost every modern gasoline and diesel car will use an EGR valve or something to the same effect. This valve helps the manufacturer meet the environmental laws and demands put on them by the country or state that they’re producing vehicles for.
What is an EGR Valve?
In the USA in 1973, the EGR was first officially produced valve. Through time it grew in popularity throughout America. It began to take off in Europe in the 1990s, as it enabled manufacturers to meet the much stricter new emission laws.
The EGR valve is part of the EGR system – one that connects from the exhaust manifold of your car and opens back up into the intake manifold (this is what brings air into the engine). The valve allows the exhaust gases to be sent into the engine with the fresh air, resulting in it igniting a second time – hence the name, exhaust gas recirculation.
Doing this results in the number of NOx gases (nitrogen oxides) being as low as possible. From an environmental point of view, NOx gases are essentially the most dangerous things that come out of the back of a car.
There are two types of NOx gases: nitrogen oxide and nitrogen dioxide. These both contribute enormously to man-made mess-ups, such as acid rain and smog.
They can also cause negative effects on your health due to ozone being produced too low down in the atmosphere and the formation of fine particles. On top of all that, in high concentrations, NOx gases can affect your breathing. The WHO sees them as a top cause of lung cancers.
In short, they aren’t good. In fact, they’re about 30 times worse than carbon dioxide for the environment.
NOx gases are formed when the engine’s internal temperature is above 1500 degrees Celcius (2732 degrees Fahrenheit).
EGR valves are a good way to combat them. Unfortunately, there is currently no way to stop them from being produced – they’re part of the chemical combustion reaction that occurs in the engine with the mixture of fuel and air. However, using exhaust gases to reduce the cylinder’s temperature results in fewer NOx gases being produced.
Why Do Cars Have EGR Valves?
Currently, for fossil-fuel-powered cars, the EGR valve is one of the most effective ways to reduce emissions (especially NOx gases) while still maintaining performance. It does this by lowering the cylinders’ temperatures, meaning that NOx gases are less likely to be formed.
This benefit is often overlooked, though, even though it’s simple: the internal temperatures within your engine’s cylinders are dramatically lower than otherwise. This is important as it decreases the likelihood of your engine to suffer knock – this is when the fuel ignites at the wrong time, due to the cylinder being too hot.
The decreased likelihood of engine knock, in turn, leads to a smoother and yet more environmentally-friendly motor.
How Does the EGR Valve Work, Then?
We’ve looked at what the EGR valve is, where it came from, and what it does, but you may be wondering, ‘How does it actually work?’
To answer that, we’ll run through the standard procedure of what should happen when you start up your engine and run your car. When you turn the key in the ignition and the engine starts, it will take a set amount of time to warm up. How long this will depend on a variety of factors, most notably your coolant and oil levels, and the temperature outside. When the engine is cold, the EGR valve remains shut.
As soon as the first few cylinders spark, exhaust gases will push out of the engine through the exhaust valves, then the exhaust manifold, and down the tailpipe. However, some will find their way down the EGR pipe.
You’ll find the EGR valve at the end of this pipe, back on the intake manifold.
As the engine begins to warm up, the valve begins to open. In most modern cars, this is done electronically, but some cars (and older models) may use a vacuum-operated valve. Temperature sensors in the engine block help the car know when this is the case. Only about 5% – 10% of the exhaust gases will end up being sent back into the engine – the rest will continue down the pipe as usual.
The valve opening allows exhaust gases back into the intake manifold. From here, they are mixed with fuel and air and then injected into the engine.
These exhaust gases mean that the concentration of oxygen is lower in the combustion chamber, leading to a reaction with less heat. The lower amount of heat results in the benefits mentioned earlier – decreased quantities of NOx gases and increased engine performance.
There are many sensors located around a car, including oxygen and temperature sensors (and many more). These sensors all provide feedback to the ECU, which is essentially the brain of the car. It uses these sensors and analyses the data to decide how open the EGR valve should be. This must be carefully regulated because if too many exhaust gases are put back into the engine, there can be a dramatic power reduction. Conversely, too little exhaust gases will lead to increased production of nitrous oxides, which are both damaging and illegal.
The valve is only open when the engine is under load and hot. This is most likely to occur during heavy acceleration or continuous, fast driving, such as on a highway. When the engine is idling, or when you’re driving smoothly, it will be shut.
Each manufacturer will have decided specific times and conditions that the valve will be open and shut.
Do Cars Need an EGR Valve by Law?
Technically – no. But they do have to meet stringent emission laws, in this particular context concerning nitrous oxides. EGR valves are likely to be by far the easiest way of doing this, especially if (like most cars today) the manufacturer has designed the car to have one.
If your car has an EGR valve (and it probably does), don’t ignore it. As well as being vital for environmental pollutant reductions, it also increases engine performance. We will go into more detail as to why you should look after your EGR valve in a moment.
Not all cars have EGR valves, though. The most advanced gasoline engines, such as those with variable valve timing (VVT), often don’t require an EGR valve.
Why You Should Look After Your EGR Valve
So you’ve come to an auto shop. The mechanic has run a diagnostic that tells you that the EGR valve is on the blink, but it doesn’t sound that important.
Well, the truth is that your car will still run without this valve – for a while. But, as we’ve said, it’s not just about pollutants. If you disconnect the valve, the engine will be under greater strain all the time. It’s more likely to knock, the exhaust valves will be under more pressure, the catalytic converter will be doing a double shift, and you’ll fail any emissions test.
In short, not fixing your EGR valve will lead to many more problems in the future. It’ll save you money, in the long run, to get it fixed.
How Do I Know My EGR Valve is Faulty?
We now come onto the main point of this article – the signs that could indicate that your EGR valve is on the blink. It could be stuck open, stuck closed, or clogged up.
- The “check engine” light is on – sensors in your car will be able to tell when the temperatures in the engine or the exhaust pipe’s oxygen content are too high, for example. Modern vehicles will also have a sensor directly linked to the EGR valve, which will let it know if it’s stuck open. If these sensors produce abnormal readings, the check engine light will come on. There could also be a problem with the sensor in this situation, so that may need replacing too.
- Decreased engine performance – if the temperatures within the cylinders are too hot and the air or fuel ratio is all wrong, you’ll notice a decrease in power. A loss of power could also be a sign of many other things, though, including a misfire, a blocked air filter, a compression leak, or a faulty fuel pump.
- When the engine is idling, it won’t feel right. You know your car better than anyone else, so if you think something’s wrong, you’re probably right. If the EGR valve is stuck open, too many exhaust gases will be entering the cylinder, resulting in less power and, therefore, a “weaker” idle.
- You’ll smell fuel in the cabin and around the car much more easily.
- The car will fail an emissions test – specifically, it will fail on nitrous oxides, or they might be of a high concentration compared to the norm.
The most foolproof way of diagnosing your EGR valve is to take it to a trained mechanic. They will attach a code reader, which will specifically state whether or not there is a problem with the valve. You can buy code readers for yourself, but this is sometimes a risky business. Code readers from unrecognized producers have been known to fry a car’s electrical system completely.
Keeping Your EGR Maintained
Your EGR valve should be cleaned or replaced about every 50,000 miles, depending on the manufacturer.
A good way to look after your EGR valve is to have it carbon cleaned. This is done by a professional, who will often be able to call out to your house to see you.
You can also purchase some engine additive cleaners to put through the intake or the fuel. Both of these will help to keep your engine clean and fresh. It also helps to use high-quality fuel (the bigger numbers on the pumps).
An EGR valve is a vital part of your car and how it functions. If you think there may be a problem, we recommend getting it looked at by a professional as soon as possible.