What is an EGR Valve?

What does the EGR valve on a car do?

An EGR valve is short for Exhaust Gas Recirculation valve. You can find an EGR valve in modern internal combustion engines (ICE) in petrol and diesel cars. An EGR valve is an important part of a vehicle’s engine management system. The EGR valve is the main component of the EGR system. The valve is usually located between the exhaust manifold and the intake manifold.

For a car engine to start and for the combustion process to occur, the vehicle must allow for a certain level of air intake. As a car is driven, air from the atmosphere is taken into the intake manifold. The intake manifold takes air and distributes it to the intake ports of the cylinder head(s) in the vehicle’s engine. Our atmosphere’s air is around 20 per cent oxygen and 80 per cent nitrogen. When the air from our atmosphere combines with fuel and ignites within the combustion chamber, temperatures reach around 1,370°C.

When temperatures get this hot in the combustion chamber, nitrogen oxide (NOx) emissions are produced. This is a by-product of the chemical reaction. 'By-product' refers to the gases which are created as a consequence of the combustion process - but not created deliberately. This is where the EGR valve comes in. The valve uses exhaust gas recirculation as a method to regulate and control the nitrogen oxide (NOx) emissions.

How does an EGR valve work?

An EGR valve has two primary settings: open and closed. The valve will be closed when the engine is starting up. The Engine Control Unit (ECU) determines the amount of gas recircled back into the engine from the exhaust. The ECU monitors various engine parameters, such as engine load, speed, and temperature, to determine the amount.

The ECU sends a signal to the EGR valve to open when it detects the EGR temperature increasing on the sensor. The EGR temperature sensor increases as more power builds from the engine and the EGR valve opens progressively wider the higher the temperature of the engine gets. The opposite happens as the engine cools, or the car starts to reduce speed. As this happens, the EGR sensor detects a temperature drop and the valve will then start to close.

This process of opening and closing the valve recycles some of the exhaust and by-product gases produced during the combustion process. The exhaust gases are then recircled back into the combustion chamber via the vehicle's intake manifold system. This is beneficial, as this process:

• Enhances engine efficiency.
• Improves fuel economy.
• Reduces harmful NOx emissions

NOx and EGR valves

NOx is produced as a by-product of the combustion process and emitted by a vehicle’s exhaust. This happens when fuel combusts in the presence of air. These harmful gasses are then passed through the vehicle’s exhaust system and into the atmosphere. An EGR valve will regulate a car's exhaust system to produce less NOx. The vehicle will then be able to meet stringent exhaust emission regulations.

Nitrogen itself makes up around 78 per cent of our atmosphere^[1]. When in isolation and airborne, it is not harmful to humans. However, a car’s combustion process relies on the engine heating rapidly. As this happens, nitrogen (N) and oxygen (O) combine, producing nitric oxide (NO) and nitrogen Ddoxide (NO2) as by-products. These are also commonly referred to as nitrogen oxides (NOx).

Over the last few decades, NOx emissions have significantly reduced. Gov.uk reports that, since 1970, NOx emissions have reduced by 78 per cent. Despite this, NOx pollution continues to be a problem in the UK. There are urban areas in the UK where levels of nitrogen dioxide pollution exceed the World Health Organization’s Global Air Quality guidelines^[2].

Manipulation of EGR valves

Some drivers opt to have their EGR removed illegally, this is known as an ‘EGR delete’. As well as being illegal in the UK, an EGR delete also has many risks. Risks include:

• Reduced horsepower
• Engine knocking noises
• Increased exhaust gas tempreture
• Engine damage

EGR tampering and manipulation have become more common with both passenger cars and heavy diesel vehicles. Research suggests that EGR manipulation could and may have already led to a rise in nitrogen oxide gases.

Types of EGR valves

In the UK, there are two main types of EGR valves. There are vacuum-operated EGR valves and electronically controlled EGR valves.

Vacuum-operated EGR valve

These types of EGR valves are typically found in older vehicles. A vacuum operated EGR valve uses a diaphragm to regulate the flow of exhaust gas. Vacuum is generated in the intake manifold by the downward movement of the piston during the combustion process. When a vacuum is applied, the diaphragm mechanism will allow the valve to open.

If the ECU detects the engine has stopped or reduced in speed, the EGR will recirculate less or no exhaust gas. When the vacuum is reduced, the spring will start to close off the valve. The spring keeps the valve closed when there is no vacuum applied.

Electronically controlled EGR valve

An electronically controlled EGR valve utilises signals from the ECU. It measures and regulates the levels of exhaust gas flow to the intake manifold. This type of valve functions with electronic actuators which control the position and movement of the valve.

It is the ECU which determines the optimal exhaust gas recirculation amount. It optimises the performance and efficiency and meeting of emission regulations. The ECU determines this based on engine parameters, including:

• Speed
• Engine temperature
• Engine torque output
• Emission levels
• Throttle position

If the ECU determines exhaust gas recirculation is necessary, it emits an electronic signal to the actuator of the EGR valve. This then opens and closes the valve as and when necessary.

EGR valve symptoms - what are the symptoms of a faulty EGR valve?

Bad EGR valve symptoms and blocked EGR valve symptoms

Increased fuel consumption

As with many engine faults, if you have a faulty or damaged EGR valve, you may find that your car is burning more fuel when you are driving it. For example, if the EGR valve gets stuck open, a vacuum leak could be created which has an adverse impact on fuel economy.

Poor performance

You may experience inferior performance when driving if the EGR is faulty. An EGR valve is a vital component to the EGR system. This system relies on the valve functioning adequately to ensure its proper flow and operation. Performance issues can include reduced power, acceleration and fuel efficiency.

Limp mode

You may experience your car going into ‘limp mode’ if you have a faulty or damaged EGR valve. Limp mode is a security feature in vehicles which activates when the ECU or transmission control unit senses a fault or problem. Limp mode will see a vehicle’s speed dramatically reduced and capped at between 30-50mph. If the ECU senses a problem with the EGR system, your car may activate limp mode.

Failing an emissions test

As part of every MOT, your vehicle undergoes an authorised exhaust emissions test. Failing this test could be because of a bad EGR. EGR valves reduce the amount of NOx pollution which is emitted from your vehicle’s exhaust. If your EGR valve is not working correctly, it would mean that your car emits higher levels of these harmful gases and therefore you would fail the test.

Knocking noises coming from your engine

Another symptom of a bad EGR is knocking noises coming from your engine. These noises can happen as a result of temperatures being too high in the combustion chamber. Without a functional EGR valve to regulate the temperature and ignite the fuel at the appropriate times, you may hear knocking noises coming from the engine and cylinder.

A rough idle

You may experience a rough idle if your EGR valve is stuck open. This is because, when open, the EGR valve provides a steady and continuous flow of exhaust gases into the intake manifold. If the valve gets stuck open, this can result in your car feeling shaky or rough when starting it up, driving or stopping the car.

Frequently stalling while idle

Like with a rough idle, you may also find that your car is stalling more frequently if your EGR valve gets stuck open. This is directly related to the steady and continuous flow of exhaust gases to your engine. If the valve cannot close when signalled by the ECU, this can lead to more frequent starting, slowing or stopping the vehicle.

Smell of fuel

When an EGR valve is not working correctly, it can lead to a strong smell of fuel in the vehicle’s cabin. This is because the valve may not be regulating and recirculating the exhaust gases correctly within the intake manifold. This leads to an excess of emissions; less fuel being burned at low revs and a strong smell of fuel as a result.

What are the causes of a faulty EGR valve?

Because of where the EGR valve operates and how it works, the valve will experience wear and tear over time. However, there are certain things to watch out for, as they can exponentiate the rate at which the valve degrades.

Build-up of carbon particles

An excessive build-up of carbon particles within the EGR valve and system can lead to the valve either becoming stuck open or closed. The tubes and exhaust gas channels becoming clogged can result in damage to the plunger mechanism of the valve.

Low-quality or contaminated fuel

Low-quality and/or contaminated fuel can also cause EGR valve faults. If low-quality or contaminated fuel enters the fuelling system, impurities also enter the system. This leads to deposits which build up within the EGR valve and prevent it from being able to open and close correctly.

Poor maintenance

As with all parts of the vehicle, the EGR system and valve requires regular maintenance. Neglecting vehicle maintenance can lead to an accumulation of carbon deposits within the EGR valve and system. This can also impact the valve’s ability to open and close appropriately. As a result, the flow of exhaust gases can become restricted and your engine has to work harder with hotter temperatures.

Faulty components

Faulty components surrounding the EGR valve or within the EGR system can cause an EGR valve to fail. For example, if the valve diaphragm is faulty, the valve can become stuck open or closed which will hinder the valve’s ability to function adequately.

Excessive or extreme engine operating conditions

The deterioration of an EGR valve can be accelerated by excessive or extreme operating conditions. Examples of extreme operating conditions could include:

• Driving for prolonged periods with a heavy load.
• Excessive levels of dust in the exhaust system.
• EGR cooler failure/engine overheating.

EGR valve replacement cost

Newer vehicles have more complex EGR systems which are facilitated by more advanced equipment and technology. This typically means that an EGR valve for a newer vehicle will be more expensive. The cost will also be dictated by the problem with your EGR valve. It may be that other components in the system also need to be fixed or replaced and this will often result in additional costs being incurred.

If you think you have a faulty EGR system or valve, Arnold Clark is always here to help. Contact your nearest local branch or book a service online today.

References

1. https://climate.nasa.gov/news/2491/10-interesting-things-about-air/
2. https://researchbriefings.files.parliament.uk/documents/POST-PN-0691/POST-PN-0691.pdf