EGR valve decoding. What is EGR and how to deal with it

Exhaust gas recirculation (EGR) system. Device. Faults.

The Exhaust Gas Recirculation (EGR) system reduces nitrogen oxide (NOx) emissions. The high temperature of the air-fuel mixture burning in the combustion chamber produces a large amount of nitrogen oxides (NOx). The exhaust gas recirculation system directs part of the exhaust gases from the cylinder head outlet through the intake manifold back to the combustion chambers, thereby lowering the combustion temperature of the air-fuel mixture, resulting in a decrease in the concentration of nitrogen oxides.

The idea is to supply some of the exhaust gases from the exhaust manifold to the intake manifold at certain engine operating modes. The increased content of nitrogen oxides in ICE emissions is caused by high temperature in the combustion chamber. Oxygen is the catalyst for the combustion reaction: the more oxygen, the higher the temperature. And if you add exhaust gases to the air, then the oxygen content in it will decrease. As a result, the combustion temperature of the mixture and, accordingly, the toxicity of exhaust gases are reduced.

EGR is installed on both gasoline (except turbocharged) and diesel engines. Due to the excess air in the diesel engine, a greater amount of nitrogen oxides is formed. In addition to improving environmental performance (NOx emissions are reduced by up to 50%), there are also some positive side effects. In gasoline engines, a portion of exhaust gases, reducing the vacuum in the intake manifold, reduces pumping losses, which helps to reduce fuel consumption by 2-3%. Cooler operation in gasoline engines reduces the risk of detonation, while diesel engines run smoother. Emission of soot from diesel engines with EGR system is reduced by 10%.

The EGR algorithm depends on the type of engine. In diesel engines, the valve opens at idle and supplies up to 50% of the intake air volume. As the speed increases, the valve closes proportionately until fully closed at maximum load. When the engine warms up, the valve is also completely closed. In gasoline engines, EGR does not turn on when the engine is cold, at idle and at maximum torque. At low and medium load, the system provides 5-10% of the air supplied to the intake.

It is worth noting that EGR often turns into a headache for our motorists. The system is quite capricious, during its operation (especially on domestic fuel), the EGR valve, the intake manifold and the sensors located in it are covered with soot, which leads to unstable engine operation. The EGR valve is an expensive part, so many car owners, instead of replacing it, resort to jamming the entire system.

Why is EGR not installed on gasoline turbo engines? On atmospheric engines, the system works practically only at medium speeds. And on turbocharged engines, the operating range is even smaller - and it turns out that the end does not justify the means. Therefore, manufacturers use other methods to reduce NOx emissions: liquid cooling of the charge air (which reduces the temperature in the combustion chamber) and continuously variable valve timing (providing internal exhaust gas recirculation). With internal recirculation, part of the exhaust gases enters the cylinder back at the moments of valve overlap, when both the intake and exhaust valves are open at the same time. Technically, overlap can also be arranged by selecting the shape of the camshaft cams, but in this case, recirculation will be carried out in all engine operating modes. In systems of stepless regulation, the overlapping of valves at the command of the control unit occurs only in the necessary modes.

Construction types

Although the principle of operation of all systems is the same, their design is very diverse. In any EGR system, the main part is the valve. The differences are in the way of managing its work and, accordingly, the composition of the elements. EGR first appeared on American cars back in the early 70s of the last century. They were pneumomechanical, that is, they were controlled only by the discharge of the intake manifold.

Like any mechanical system, it did not differ in high accuracy. With the introduction of electronic engine management systems, EGR became electro-pneumatic (Euro-2 and -3), and later fully electronic (Euro-4 and -5) appeared.

The EGR valve can be mounted on the intake manifold, in the intake tract, or directly on the throttle body. Since the EGR system in diesel engines bypasses a larger amount of exhaust gases, the valves in such systems also have a bypass hole of a larger diameter compared to gasoline ones. In some diesel engines, especially turbocharged ones, intake pressure can exceed exhaust pressure, making exhaust gas recirculation impossible. In such cases, control (swirl) flaps are installed in the inlet pipeline to create the necessary reduced pressure.

The main malfunctions of the EGR system

If the EGR system malfunctions, erratic idle speeds can be observed and the engine often stalls. There is also erratic operation at wide open throttle, interruptions when decelerating, detonation, misfiring.

All malfunctions come down to two main reasons:

1. Not enough exhaust gas is passing through the EGR valve.
2. Too much exhaust gas is passing through the EGR valve.

The components of the EGR system in which malfunctions may occur are as follows:

External pipes (or channels in the intake manifold) for supplying exhaust gases.

The actual EGR valve.

Thermal valve that connects a vacuum source to the EGR pan, depending on the temperature of the coolant or air.

Solenoids, electric or digital valves controlled by the ECU.

Integrated or separate exhaust gas pressure transducers.

Malfunctions of channels and EGR valve
When the channels are contaminated, the recirculation flow decreases, and the environmental pollution with nitrogen oxides N0x increases. Since the driving characteristics hardly change at the same time, drivers rarely complain about such a malfunction. Sometimes knocking may occur and engine efficiency may deteriorate (ECU does not go into closed mode).
The EGR valve that does not open also manifests itself. The design of the valve provides for its locking in case of malfunctions in the EGR system.
Particulate matter from the exhaust gases settle unevenly in the EGR valve locking device and gradually the valve does not close tightly. In this case, exhaust gas recirculation begins to occur constantly. This situation will be reflected in the stream of parameters received by the scanner from the ECU, but for final conclusions about the state of the valve, it should be disassembled. After cleaning and before installing the valve, make sure that the channels are free from pieces of deposits that can re-clog the system.

A non-closing valve usually manifests itself as follows:

1. Idle instability, frequent engine shutdowns, misfiring.
2. Jerks of the car when driving.
3. Reducing the vacuum in the intake manifold and, as a result, the operation of the injection engine on a rich TV mixture.

The EGR valve itself is a relatively simple device, but the system that controls it is quite complex. Before dismantling the valve, make sure that the control system is in good condition.
The vehicle owner's manual recommends regular inspection and cleaning of the EGR valve and passages. But drivers usually neglect this, until the system fails completely.

Vacuum signal out of range
A weak or no vacuum signal will not open the air valve, but a constant vacuum will keep the valve open all the time. In such cases, the correct connection of the vacuum hoses and the vacuum at the valve should be checked.
In systems using vacuum in the induction diffuser, a vacuum booster is used, a malfunction of which can lead to the vacuum signal from the EGR valve being turned off or vice versa - to its constant supply.
A properly functioning EGR system is disabled when the engine warms up by blocking the vacuum signal with a thermal valve. A thermal valve failure will result in excessive nitrogen oxide pollution (if the thermal valve is permanently closed) or erratic idling and poor throttle response (if the thermal valve is permanently open).
In some systems, the EGR valve is opened by the combined action of vacuum and exhaust pressure signals. In such systems, even with good vacuum, the EGR valve will not open if some components of the exhaust port have been changed to non-standard, with a lower resistance to gas flow (exhaust gas pressure will drop).

In electronic engine management systems, permission is given to the EGR valve diaphragm through the solenoid valve. The solenoid valve can operate on the principle of open - closed or with pulse-width modulation. In such systems, it is necessary to check the electrical signal from the computer to the solenoid valve solenoid, the solenoid itself, the integrity of the vacuum supply channels from the source to the EGR valve.
The set of controlled parameters of the EGR system read by an automotive diagnostic scanner depends on the specific car model, as a rule, these are the following parameters:

1. The value of the recirculation flow in percent.
2. Filling factor of the control signal during operation of the solenoid valve according to the principle of pulse-width modulation.
3. Switching state of the EGR valve (on-off).

Diagnosis of the EGR system.

To figure out whether the EGR valve should work in specific conditions, you should use the technical documentation of the specific car.

Diagnostics of the main components of the pneumomechanical EGR system
For diagnostics, technical documentation from the manufacturer and measuring instruments are required: an automotive multimeter, a pressure gauge, a hand vacuum pump, a logic probe and an oscilloscope. It will not be superfluous to have a diagnostic tool or a scanner to display error information and the necessary current data.

Diagnostics of the thermal valve, sensors and solenoids
1. The voltmeter controls the voltage at the contacts of the solenoids in the current and de-energized modes.
2. An ohmmeter checks the resistance of the windings of the sensors and solenoids and the presence of a short to ground.

3. With the help of a vacuum pump and a pressure gauge, the correct operation of the electro and thermal valves is checked.

4. Using an oscilloscope or a diagnostic scanner, you can check the output signals of all sensors used by the ECU for EGR control: throttle position, crankshaft speed, intake manifold vacuum, etc.

Diagnostics of the main valve of the EGR system
A typical main valve failure is a leaky diaphragm in the vacuum chamber or a loose valve closure due to contamination.
In EGR systems without the use of exhaust gas backpressure, the valve is removed from the engine, a manual vacuum pump is connected to its vacuum inlet, and a vacuum of about 250 mm Hg is applied. Art. The valve stem must retract, and the locking device must open, the applied vacuum must not change, and the stem must change its position, for at least 30 s. Otherwise, the diaphragm is leaking and the valve should be replaced.
In EGR systems using exhaust gas backpressure, it is pointless to remove the main EGR valve, since without exhaust gas pressure it will not work, even if it is in good condition. In this case, it is necessary to follow the manufacturer's recommended inspection procedures, which usually include restricting the passage of exhaust gases through the exhaust pipe.

Diagnostics of EGR systems with electronic control
Electropneumatic systems (EPS)
Vacuum is supplied to the EGR system (EPS) through a normally open solenoid valve, which is controlled by the ECU. When the fuel control system is in open mode, the ECU closes the solenoid solenoid contact to ground with a transistor switch, blocking the supply of vacuum to the EGR valve. If the EGR valve is open in an inappropriate engine operating mode, then this indicates that there is no connection to the solenoid contact of the solenoid valve to ground or there is no supply voltage on the other contact of its winding. If the EGR valve does not open, the connection between the ECU and the solenoid contact is shorted to ground outside the ECU.
Pulse width modulation can be used to control the recirculation flow. The ECU periodically closes the solenoid contact of the solenoid valve to ground. The ratio of the duration of the on state of the solenoid to the period is called the duty cycle, which is measured in percent. Typically, 0% corresponds to blocking the supply of vacuum to the valve, and 100% corresponds to a fully open valve.
Using a multimeter connected with probes to terminal B (fig. below) and "mass", you can control the switching frequency of the solenoid and the duty cycle by the average value of the voltage on the winding. An oscilloscope for such measurements gives a more visual picture than a multimeter.

For diagnostic purposes, a vacuum key is built into the EGR valve (fig. below). The ECU uses the key signal to check for vacuum in EGR valve vacuum line 1. A working key works synchronously with the solenoid valve; its electrical signal can be monitored using a multimeter, oscilloscope or logic probe connected to pin C in connector 6.

1 - vacuum line to the EGR valve;
2 - line to the source of rarefaction;
3 - diagnostic normally open vacuum key;
4 - locking spring;
5 - normally closed by spring 4 and de-energized solenoid valve;
6 - connector;
7 - power bus;
8- ECU

Checking the EGR valve servo

Check that the sound of the EGR valve servo (stepper motor) is clearly audible when the ignition is turned on (without starting the engine). If no sound is heard from the EGR valve servo, check the servo power circuits. If the power supply circuit is working, then the servo itself or the electronic engine control unit may be faulty.

Checking the resistance of the servo winding

Disconnect the EGR valve servo connector. Measure the resistance between pin 2 and pin 1 or 3 of the servo connector. Rated resistance: 20-24 ohms (at 20°C). Measure the resistance between pin 5 and pin 4 or 6 of the servo connector. Rated resistance: 20-24 ohms (at 20°C). Replace the gasket and tighten the valve mounting bolts to rated torque.

Checking the operation of the servo

Connect the test harness to the EGR servo connector. Connect a wire from the positive terminal of the power supply (voltage approximately 12 V) to terminal "2" of the servo connector. Connect the wire from the negative terminal of the 12 V power supply to terminals "1" and "3" of the connector. At the same time, check if you can feel a slight vibration of the running stepper motor.

The resource of various EGR systems ranges from 70 to 100 thousand kilometers (in domestic conditions, about 50 thousand). After that, its components must be replaced. This is ideal. However, there are few who want to pay a lot of money. Simple and timely maintenance of the system will help extend its life. In the EGR air valve, it is necessary to periodically clean the seat and stem from carbon deposits with a carburetor cleaner. This must be done carefully so that the liquid, which is aggressive to rubber, does not damage it if it gets on the valve diaphragm. In systems with a control solenoid valve, it usually has a filter that protects the vacuum system from contamination. It needs to be cleaned up.

When the EGR starts to fail, many car owners prefer to muffle it. As a rule, this is done using a gasket cut from thin sheet metal, installed under the valve. Among specialists, opinions about jamming the system differ. Some consider it completely harmless, and some even consider it useful. The latter believe that as a result, the temperature in the combustion chamber rises, and this increases the risk of cracks in the cylinder head.

Simply mechanically killing the valve and removing swirl flaps (where present) does not always produce the desired results. On turbodiesels, there may be problems with the regulation of boost pressure and increased wear on the turbine. On modern engines, the EGR valve must be "deleted" and programmatically by flashing the control unit. Otherwise, the controller will constantly generate an error or even put the engine into emergency mode.

The automotive EGR system - Exhaust Gas Recirculation, is a very ambiguous and rather capricious thing, especially with the very low quality of fuel that is found in our area, quite often. The ambiguity of this system lies in the fact that its purpose is purely ecological. The reverse exhaust gas recirculation system, or USR, is designed to reduce the amount of nitrogen oxides in automobile exhaust. What is the USR, why is it needed and how are its malfunctions expressed, we will talk about all this now.

You should start with the fact that the USR system is installed on most diesel engines and gasoline, atmospheric units. The essence of this system is that at certain moments the EGR valve opens and a portion of exhaust gases is thrown into the engine intake manifold.

Schematic representation of the operation of the USR system.

Thus, the amount of oxygen in the fuel mixture decreases, which in turn reduces the temperature of its combustion. And at a lower combustion temperature, the amount of nitrogen oxides in car exhaust decreases quite significantly. If the engine is turbocharged, then the range of application of the USR is significantly narrowed, which makes its installation not rational. In such cases, other solutions are applied that reduce the amount of harmful components of automobile exhaust.

Exhaust Gas Recirculation does not work at idle, it is not used when the engine is cold, and the EGR valve closes when the throttle is at full throttle.

USR system management

The exhaust gas recirculation system is controlled by an electronic engine control unit. And the command to open or close the EGR valve can be given based on:

• coolant temperature sensor;
• crankshaft sensor;
• throttle position sensor;

In various car models, either all of the listed sensors, or some of them, and in some cases, only the coolant temperature sensor are used to control the USR valve.

What does the EGR valve look like on a Chevrolet Lacetti

One way or another, but the operation of the USR valve is always controlled by automotive electronics. And while this system is functioning properly, the driver of its work, almost does not feel. The useful work of the USR system outside of environmental issues is very subtle. This system saves about three percent of fuel on gasoline engines. Also in some cases, the USR system prevents detonation of fuel in the engine. But, this phenomenon in itself is rare and extraordinary. As for diesel units, if there is a properly functioning EGR system, they work more smoothly, softly, and quietly. In addition, in engines running on diesel fuel, by means of the USR, the formation of soot is reduced. That's all the bonuses that the exhaust gas recirculation system provides to the owner.

Video about USR

Why is the EGR blocked?

You can often see a situation where the USR system is simply muffled. What's the matter, not all the motorists who do this do not care about the harm from car exhaust?

In fact, the problem lies in the quality of the fuel our cars run on. The low quality of the fuel, among other things, causes the formation of soot and its deposition on the USR valve, as well as in its line. This leads to the fact that the system either does not work at all, or does not work correctly. In both cases, it is easier to drown it out, because replacing even just the USR valve is by no means a cheap pleasure. So people solve the problem, so to speak, radically. And since turning off the USR does not entail any special losses, they decide to take this step, as a rule, without much hesitation.

Gasket for USR plug (with one hole) and standard (Chevrolet Lacetti).

Silencing the exhaust gas recirculation system on gasoline engines can be done by installing a conventional washer in the valve clearance. If swirl flaps in the intake manifold are used to regulate the EGR valve, they must be removed, too. In diesel engines, in addition to mechanically shutting off the USR valve, it is necessary to disable it programmatically. Otherwise, the wear of the turbine increases and the stability of the power unit is disturbed.

Disputes over jamming the USR continue to this day. Some believe that it is possible and necessary to turn off this system, while others argue that after turning it off, the combustion temperature in the cylinders increases, which leads to faster engine life and wear.

Malfunctions of the EGR system

Diagnosing problems with the described system is not as simple a task as it might seem at first glance. The trouble is that there are no pronounced symptoms that are specific to EGR problems. The engine seems to be troit, it seems to fail, but it seems not. And only a professional can suspect the exhaust gas recirculation system, in such an unstable operation of the engine. But before that, various sensors, components and systems of the car are checked. Actually, what problems can arise here:

• deposition on the parts of the USR valve, soot and other elements, leading to jamming it in any position;
• burnout of the EGR valve;
• clogging of the EGR line itself;
• violation of the electronic control systems of the USR valve;

If the valve or line is simply clogged, it is not difficult to clean them, in general, although in some cases such cleaning is simply impossible. Well, if the valve is burned out, then you will have to change it, and this, as already mentioned, is by no means cheap.

Symptoms that are specific to problems with the USR valve are virtually absent. This is, for example, unstable engine operation, at idle, unmotivated dips in power, lack of pronounced acceleration at full throttle opening, and other signs of engine malfunctions.

One way or another, do not rush to change the EGR valve or turn it off if there is no obvious damage to the valve and its parts. Perhaps the problem here is not entirely in the USR, because this system is closely interconnected with other nodes and systems for regulating the air supply and exhaust gases.

EGR valves in exhaust gas recirculation systems.

At combustion temperatures above 1371°C (2500°F), nitrogen (which makes up 80% of the atmosphere) mixes with oxygen to form oxides of nitrogen (NOx), a dangerous air pollutant.
In the cylinders of a running engine, under certain conditions, a combustion temperature much higher than the usual level occurs, while NOx emissions increase sharply.
In this regard, the exhaust gas recirculation (EGR) system, a system that reduces NOx emissions, was developed.
The main element of the system is the EGR valve installed on the intake manifold. When the air-fuel ratio is high (lean mixture), the combustion temperature is also high, more NOx is produced. To lower the air-fuel ratio, the EGR valve introduces a metered amount of exhaust gas into the intake manifold, changing the proportion of incoming oxygen in the cylinder air-fuel mixture. This system changes the mode of fuel combustion at high temperatures and reduces the formation of NOx.
NOx emissions during acceleration or high engine speeds apply exclusively to a gasoline engine. Under the same conditions, the need for an EGR system in diesel engines is eliminated or very small.
California has a stricter NOx standard than the rest of the US. Therefore, some engines sold in California had different EGR systems from those sold in other states.
On a cold engine, EGR can cause engine drivability problems. Different car models use different methods to activate the EGR system as the engine warms up.

Rice. 1 Exhaust gas recirculation (EGR) system

Varieties of EGR valves

Engines with different performance characteristics cause the use of two classifications of EGR valves: mechanical and electronic.
There are currently five types of mechanical EGR valves and three types of electronic EGR valves.

Identification of mechanical EGR valves

The mechanical EGR valves listed here are stamped with an identification number on the top of the valve.
• EGR valve (Port EGR Valve) directly mounted on the throttle body
• EGR valve with positive backpressure (Positive Backpressure EGR Valve)
• EGR valve with negative backpressure (Negative Backpressure EGR Valve)

On a note:

Since 1984 EGR valves have a label: "N" (negative) or "P" (positive) imprinted on the valve cover.
Until 1984 valves can be identified by the design of the diaphragm plate.

Identification of electronic EGR valves

EGR VALVES - MECHANICAL

Port EGR Valve

Throttle body mounted EGR valve (Port EGR Valve), the vacuum diaphragm in the Port EGR Valve (Fig. 2) is connected to a vacuum port located in the carburetor, TBI, or MPFI throttle body. Calibrated vacuum ports transmit a vacuum signal, depending on the vacuum of the intake manifold, excluding x/stroke mode, to the EGR valve membrane.

Rice. 2 Port EGR Valve

When the throttle valves are opened, vacuum flows through the hole to the vacuum diaphragm in the EGR valve, through the connecting hose. When the vacuum signal reaches a certain level, the diaphragm moves up against the calibrated spring force, moving the plunger with it. The valve plunger opens the port, allowing exhaust gas to flow from the exhaust manifold to the intake manifold and into the engine cylinders.
During c/stroke when the vacuum port is closed, or in other cases where the intake manifold vacuum is very low, such as in the case of wide open throttle, there is not enough vacuum to control the EGR diaphragm, the plunger remains in place and no exhaust gas enters into the intake manifold.
Gas recirculation occurs during periods of normal intake manifold vacuum when the throttle is not in c/stroke mode.

On later engine designs, the vacuum signals are controlled by the Electronic Vacuum Regulator Valve (EVRV) using a pulse-width modulated solenoid. The ECM controls the EVRV using information from the following sensors:
• Intake manifold vacuum sensor (MAP).
• Engine speed sensor (CKP).

The ECM controls the solenoid using the Pulse Width Modulation (PWM) principle. The ECM activates the solenoid at high frequency, changing the flow of exhaust gases.

Positive Backpressure EGR Valve

The Positive Backpressure EGR Valve, developed in 1977, uses both engine vacuum and exhaust pressure to control the amount of recirculation flow. This provides improved recirculation during heavy engine loads.
A control valve located in the EGR system acts as a vacuum/pressure regulator (Fig. 3).
This valve controls the amount of vacuum in the diaphragm compartment. When the control valve receives a sufficient exhaust pressure signal through the hollow shaft, the pressure force overcomes the light spring, closing the hole under the diaphragm. In this case, the maximum vacuum force is supplied to the diaphragm.
The metal baffle prevents hot exhaust gases from heating up the diaphragm.

Rice. 3 Positive Backpressure EGR Valve

If the vacuum level decreases in the diaphragm chamber, such as during c/stroke or wide open throttle, the EGR valve will not open. If the pressure in the exhaust manifold is low, then the control valve will remain open and the EGR valve will also not open. However, if there is enough vacuum in the diaphragm chamber and high enough pressure in the exhaust to close the control valve, then the diaphragm lifts the cone plunger, recirculating the exhaust gases.
Once the plunger is moved, the exhaust back pressure is reduced in the hollow shaft, allowing the spring to re-open the control valve. The vacuum in the diaphragm compartment disappears and the plunger valve begins to close. The pressure in the hollow shaft increases and the control valve closes again, starting the cycle again.
This cycle occurs approximately thirty times per second during normal engine operation. If the intake manifold vacuum is very low (wide open throttle) or the throttle is almost closed (stroke mode), the Positive Backpressure EGR Valve will adjust the amount of EGR in proportion to engine load.
If the vacuum is sufficient to drive the EGR valve, the recirculation mode cycles slower as exhaust pressure increases, and quicker as exhaust pressure decreases.
On later engines, the EGR system is controlled by the ECM. A control solenoid is used in the vacuum line.
The ECM activates the EGR solenoid when the engine is cold or when other specific engine conditions occur.

Negative Backpressure EGR Valve

The Negative Backpressure EGR Valve, developed in 1979, is similar to the Positive Backpressure EGR Valve except that the regulator valve spring is lower instead of higher than the regulator valve and the regulator valve is normally closed (Figure 4).
The control valve is opened against the spring force by a negative back pressure (small vacuum in the hollow shaft). This design improves the EGR system under low exhaust pressure conditions.

Rice. 4 Negative Backpressure EGR Valve

If there is not enough vacuum in the diaphragm chamber, such as in c/stroke or wide open throttle, the EGR valve will not open. However, if there is enough vacuum in the compartment, the plunger rises, opening the EGR valve.
Since the vacuum in the plunger chamber decreases as the intake manifold vacuum decreases, a small level of vacuum (negative back pressure) is generated. This vacuum opens the control valve, filling the diaphragm chamber with air, causing the plunger to fall. Then the vacuum in the plunger decreases (exhaust pressure increases), a large spring closes the regulator valve and the cycle repeats again. This process occurs approximately thirty times per second during normal engine operation.

With enough vacuum in the intake manifold to drive the EGR valve, the EGR valve's opening frequency increases when exhaust manifold pressure is high and decreases when exhaust manifold pressure drops. On later engines, EGR flow is controlled by a vacuum solenoid that is activated by the ECM using pulse width modulation (PWM).

The ECM uses information from the following sensors to control the EGR solenoid:
• Engine temperature sensor (CTS).
• Intake manifold vacuum sensor (MAP) or air flow sensor (MAF).
• Throttle position sensor (TPS).

USE OF EGR IN ELECTRONIC FUEL INJECTION (EFI)

On vehicles with an EFI fuel system, the EGR is controlled by the engine computer (ECU).
When the engine reaches a certain temperature, the ECU sends a signal to an electric valve that provides vacuum to the EGR valve.

ELECTRONIC EGR VALVES

Integrated Electronic EGR Valve (IEEGR)

In 1987, a fundamentally new EGR valve was introduced, which was controlled electronically.
The Integrated Electronic EGR Valve (IEEGR) works like a valve with a remote vacuum regulator, except that the regulator and pintle position sensor are assembled in a non-separable assembly (Fig. 5). The regulator and the position sensor are not serviced or repaired.
The ECM controls the vacuum regulator with pulsating current. This pulsating current determines the gas recirculation flow. Of the input signals, the signal from the intake manifold discharge sensor (MAP) or the intake air flow sensor (MAF), the coolant temperature sensor (CTS), and the engine speed sensor (CKP) are used.
The IEEGR valve receives a Pulse Width Modulated (PWM) pulsating current signal from the ECM, converts it via an internal voltage regulator to a specific voltage level, which controls the vacuum solenoid.
When the vacuum solenoid valve is open, the vacuum line is connected to the atmosphere. When the valve is closed, vacuum creates a vacuum in the diaphragm chamber, causing the diaphragm to rise and open the valve on the plunger, creating an exhaust gas recirculation flow.

Rice. 5 Integrated Electronic EGR Valve (IEEGR))

The pintle position sensor, located above the diaphragm assembly, is used to determine the position of the diaphragm and valve on the plunger during EGR operation.
If the plunger position sensor does not detect movement of the diaphragm assembly, the ECM will set a DTC.
The IEEGR is easily identified by its non-separable black plastic top cover. The IEEGR filter can be serviced or replaced separately from the IEEGR valve.

Discrete 3-solenoid valve EGR (Tri-Solenoid Digital EGR Valve)

The 3 solenoid EGR valve was introduced in 1988. The discrete EGR valve (Fig. 6) works by combining orifices (various sizes) to control the amount of EGR flow in the engine.
This is achieved by two or three individually actuated solenoids with an armature consisting of a core and a plunger with a valve that shuts off or allows the flow of exhaust gases through a hole of a certain section. This principle of operation of the EGR valve ensures greater accuracy of the recirculation flow, as the flow depends only on the set of cross-sections of the passage holes and does not depend on the accuracy of the position of the plunger with the valve relative to the valve seat.
The improved sealing of the port in the closed state completely eliminates the leakage of exhaust gases into the intake manifold.

Rice. 6 Discrete 3-valve EGR

The discrete EGR valve is exclusively controlled by the engine computer (ECM). The ECM monitors various engine parameters:
• Throttle position sensor (TPS),
• Intake manifold vacuum sensor (MAP) or air mass sensor (MAF),

Output signals from the ECM to the EGR system indicate the proper amount of exhaust gas flow needed to lower the combustion temperature.
This electronic exhaust flow control device is ten times faster than vacuum controlled models.
The solenoids are activated by a 12-volt voltage connected to the valve through an electrical connector. Electric current, passing through the windings of the selected solenoids, creates an electromagnetic field. This causes the armature to pull upward, pulling the valve plungers off the base.
Exhaust gas flows from the exhaust manifold to the intake manifold. If too much exhaust gas enters the combustion chamber, combustion will not occur. Therefore, the flow of exhaust gas is interrupted when the engine is in idle mode.

The EGR is normally activated under the following conditions:
• The engine is warm.
• Engine rpm is higher than idle.

Discrete EGR valve assembly is replaceable only (maintenance free).

Discrete 2-solenoid valve EGR (Dual-Solenoid Digital EGR Valve)

A discrete 2 solenoid EGR valve (Fig. 7) was installed on 1990 engines. 2.3L RPO LD2 Quad 4 ("W" vehicles by GM).
This device controls EGR flow to the intake manifold through one larger and one smaller port, giving three possible flow combinations. When any solenoid is activated, its shaft and valve armature opens the orifice. The flow depends on the orifice size of the throttle, which is precisely controlled by the ECM.

Rice. 7 Discrete 2-solenoid valve EGR (Dual-Solenoid Digital EGR Valve)

Exhaust gas leakage in idle mode is minimal, because valves are completely independent of intake manifold vacuum. The design is very reliable, special seals of the dosing holes are used.
The plungers are isolated from the exhaust compartment by a floating seal. The solenoids are fixed together to increase reliability and isolate the windings from the environment.
The discrete EGR valve is controlled by ECM (ECM Quad Driver) electronic keys that ground each respective solenoid coil circuit. This activates the solenoid, raises the valve plunger and allows exhaust gas to flow into the intake manifold.

Linear EGR valve

The linear EGR system was developed and put into production in 1992. The combustion temperature is lowered when a metered amount of the exhaust gas/intake air mixture is redirected (recirculated) to the engine intake manifold. The proportions of the mixture depend on the height of the lift of the valve plug relative to the hole in the valve base (Fig. 8).

Rice. 8 Inline EGR Valve

Features of the EGR linear system

The linear EGR system provides the most accurate control of exhaust gas flow, maximum response and diagnostic capability. The accuracy of flow control in a linear EGR system depends only on the relative position of the valve plug.
The EGR inline valve is exclusively controlled by the engine computer (ECM). The ECM monitors various engine parameters:
• Throttle position sensor (TPS).
• Intake manifold vacuum sensor (MAP).
• Coolant temperature sensor (CTS).
• Plunger position sensor (PPS).

The sensor readings are analyzed by the ECM and a signal is sent to the EGR system proportional to the amount of exhaust gases needed to lower combustion temperatures. This electronic exhaust metering is ten times faster than vacuum controlled models, and has improved diagnostic and damage detection capabilities.

The electrical connector located at the top of the housing has 5 pins:
• A - PWM signal from ECM
• E - positive voltage from the ignition system
• B, C, and D are pins from the plunger position sensor to the ECM (B is sensor ground, C is sensor signal, and D is +5 volt power)

The solenoid coil is powered by 12 volts, which is applied to the valve through the electrical connector (terminal E), then flows through the solenoid coil to the ECM, creating an electromagnetic field. This causes the armature to pull upward, lifting the plunger in a pulsating motion away from the base. Exhaust gas flows from the exhaust manifold (through the port) to the intake manifold.
The lift is measured by the plunger position sensor and the ECM corrects the actual plunger position from the calculated position by varying the pulse width to the solenoid until the actual plunger position equals the calculated position. This ensures the accuracy of the flow of exhaust gases into the intake manifold.
In most non-linear EGR designs, the flow is not corrected, since in these systems there is no feedback mechanism to control the actual flow and correct it.
The linear EGR valve is unique in that the ECM continuously monitors the plunger lift and continually adjusts it to get accurate flow, which is why the linear EGR system is referred to as a "feedback" system.
When the solenoid is de-energized, the plunger closes the port, blocking the flow of exhaust gases to the intake manifold.

Description of Linear EGR System Control

To control the flow of exhaust gases to the engine, the ECM controls the coil of the linear EGR solenoid to directly change the position of the plunger relative to the closed state.
The linear EGR valve contains a position sensor (potentiometer) that changes voltage in proportion to the position of the plunger. This signal is used by the ECM as feedback for exhaust flow control, engine management system diagnostics, air/fuel mixture correction, and ignition timing correction.
The ECM analyzes the plug position sensor voltages in the valve closed position and uses the exact voltage/sensor travel relationship to control the plug travel to the wide open position corresponding to 6.25 mm (fully open valve).
Similar to the Throttle Position Sensor (TPS), the plunger position is 0% when the valve is closed, and 100% when the valve is wide open, corresponding to a distance of 6.25mm.
The ECM controls EGR flow to the engine through two feedback loops:

1. The ECM sets the desired plunger position (0-100%) based on the following conditions:
• Engine speed.
• Intake manifold collapse.
• Atmosphere pressure.
• Coolant temperature.

The ECM disables the EGR system by setting the plunger position to 0% under the following conditions:
• Low vehicle speed
• X / move mode.
• Re-enrichment of the air-fuel mixture.
• Wide open throttle.
• Low engine speed.
• Cold state of the engine.

2 . The ECM controls, via PWM (Pulse Width Modulation), the duty cycle of the EGR solenoid to set the desired plunger position corresponding to the calculated one.
Opening the valve increases the duty cycle pulse width, closing the valve decreases the duty cycle pulse width.
Changing conditions such as intake manifold pressure, vehicle voltage, and valve temperature require the ECM to use a feedback loop to minimize plunger position error.
Based on the actual position of the EGR plunger, the fuel delivery amount and sparking are corrected.
The inline EGR valve part number is laser engraved and located on the top surface of the valve, near the plunger position sensor (PPS) and electrical connector.
When replacing an inline EGR valve, always check the part number, which must match the parts catalog for the vehicle model.

The EGR (Exhaust Gas Recirculation) system is a solution that reduces the level of nitrogen oxides in the exhaust gases of a gasoline or diesel engine. This system in relation to modern internal combustion engines is absent only on gasoline ones.

The main task of the EGR system is to effectively reduce the level of nitrogen oxides in the exhaust. The formation of nitrogen oxides during engine operation is caused by high temperatures. The increase in temperature in the combustion chamber leads to an active increase in the content of nitrogen oxides in the fuel-air mixture. The high temperature in the combustion chamber of the internal combustion engine leads to the fact that oxygen and nitrogen, which are contained in the supplied air, begin to interact with each other.

Air enters the heated combustion chamber of the engine, where nitrogen oxides are further actively formed. This means that oxygen, which is necessary for the full combustion of gasoline in units of this type, begins to be replaced by the indicated nitrogen oxides. The working mixture, under the condition of a lack of oxygen, does not burn out completely, as a result of which engine power is lost, fuel consumption increases markedly, and the toxicity of ICE exhaust gases also increases.

By returning part of the exhaust gases to the intake manifold, this slightly lowers the combustion temperature of the air-fuel mixture. Lowering the temperature automatically reduces the rate of formation of nitrogen oxides.

The ingress of part of the exhaust gases back into the intake practically does not change the required ratio of basic components to obtain a high-quality fuel-air mixture, the engine itself does not lose power in various modes, and fuel economy is also observed.

Disabling the EGR valve

In Europe and other developed countries, environmental issues are approached quite strictly. There are many disputes on the territory of the CIS on the issue of the USR. The topics of discussion among motorists are topics regarding how to “mute” the EGR of a diesel or gasoline engine, neutralize the exhaust gas recirculation system, turn off the EGR valve of a diesel engine, etc.

Many are sure that the recirculation system “strangles” the engine and the USR takes power, preventing the engine cylinders from being filled with clean air to the fullest. These include amateurs. An equally common reason for refusal to recirculate is the severe contamination of the intake manifold and the rapid failure of the system sensors, as well as the EGR valve.

All elements of the recirculation system suffer from carbon deposits when the engine is operated on low-quality fuel. Repair of the system requires certain financial costs. Some drivers, for this reason, immediately “suppress” the exhaust gas recirculation and do not care about the advisability of such a solution.

Exhaust gas recirculation: EGR valve

The main element of the exhaust gas recirculation system is the EGR valve. The entire system is based on this valve. It is the USR valve that is the solution that allows a certain part of the exhaust gases to enter the intake manifold, where they are then mixed again with the next portion of the air entering the intake.

The more oxygen is in the combustion chamber, the higher the combustion temperature of the fuel-air mixture. Adding part of the exhaust gases to the mixture means a forced reduction in the amount of oxygen. Thus, a decrease in the combustion temperature of the working mixture in the chamber is achieved. Less oxygen means less interaction with nitrogen, which ultimately reduces the amount of nitrogen oxides in the exhaust.

The EGR valve of a diesel or gasoline engine does not work the same, which depends on the characteristics of a particular type of internal combustion engine. The diesel engine has an EGR valve that opens at idle, halving the intake of fresh air. As the load on the engine increases, the EGR passes less exhaust gases into the intake, and at times of peak loads, the valve is completely closed. This valve also closes when the diesel engine is warming up. As for gasoline ICEs, the EGR valve is closed at idle, as well as during the engine reaching maximum torque. If the load on the motor is low or medium, then the valve provides only up to 10% of the air intake.

Recirculation systems operate on the principle of a closed circuit, and the EGR valve itself can be controlled:

• electrical controller;
• electropneumatically;

For the first solution, the system relies on data that comes from the position sensor to the internal combustion engine controller. It is the controller that sends the control signal to the valve. In the second case, the EGR valve is adjusted based on the readings from the intake manifold pressure sensor, the mass air flow sensor and the intake air temperature sensor.

There are engine designs that imply improved exhaust gas cooling during the operation of the recirculation system. The EGR valve in such designs is integrated into the engine cooling system. The system becomes more complex, but nitrogen oxide levels are reduced even more effectively.

According to manufacturers, the exhaust gas recirculation system has a certain number of advantages during the operation of internal combustion engines. For gasoline engines, the advantage of the USR is a lower pressure drop in the throttle area. The lower combustion temperature reduces knocking, allowing for earlier ignition for better engine torque. A diesel engine with an EGR runs softer and quieter at idle, as a lower oxygen content leads to a decrease in pressure at the time of combustion of the fuel-air mixture.

Types of diesel exhaust gas recirculation systems

High pressure EGR is installed on diesel engines that meet the requirements of Euro 4. The permissible content of nitrogen oxide in the exhaust gases according to these requirements should not exceed 0.25 g / km. The high pressure recirculation system partially removes exhaust gases from the exhaust manifold of the turbodiesel, taking them before the turbine. Next, the system redirects these gases to the channel, from where they enter the intake manifold.

The system has the following elements in its device:

• recirculation valve with electric or pneumatic actuator;
• branch pipes for removal of the fulfilled gases;

The recirculation valve (EGR valve) bypasses exhaust gases from the exhaust system to the intake. The pneumatic valve works due to the vacuum that is created in the intake manifold of gasoline ICEs. In diesel units, this vacuum is created by a vacuum pump. The vacuum that acts on the recirculation valve is in turn controlled by a control solenoid valve.

The exhaust gas recirculation process becomes more or less intense depending on the different operating modes of the power unit. The degree of intensity directly depends on the difference in pressure at the inlet and outlet. The pressure in the intake system is controlled by a throttle valve. A closed throttle means the intake pressure drops. At this point, exhaust gas recirculation proceeds more intensively. Large recirculation leads to a decrease in the flow of exhaust gases, which is directed to the turbocharger. It turns out that at the time of active exhaust gas recirculation, the turbocharging pressure of a diesel engine, which is equipped with a similar type of USR, drops slightly.

The USR system is not active in idle mode, at the moment of full throttle opening, as well as during engine warm-up and until the engine reaches operating temperature. Control over the operation of the recirculation system is carried out. The recirculation valve comes into operation at the signal of the internal combustion engine electronic control unit, which controls the position of the throttle valve using a potentiometric sensor.

Diesel internal combustion engines that comply with the Euro 5 standard imply a level of nitrogen oxide in the exhaust gases that should not exceed 0.18 g / km. These engines have a low pressure EGR system. A feature of this system is that the exhaust gases are removed behind the diesel particulate filter. Further, the gases enter the radiator of the recirculation system for additional cooling. The next step is the passage of gases through the recirculation valve and penetration into the intake in front of the turbine.

The low pressure EGR system provides the following benefits:

• reducing the amount of soot particles;
• exhaust gas temperature is effectively lowered;
• a significant reduction in the level of nitrogen oxides in exhaust gases;

An additional plus is that the exhaust gases pass through the turbocharger. This allows this recirculation system to work efficiently without reducing the boost pressure. It turns out that the engine runs without loss of power.

The recirculation rate is implemented by the engine ECU. Control is carried out using the following elements:

• throttle valve;
• recirculation damper;
• exhaust flap;

All dampers function due to the presence of an electric drive. The opening of the dampers by one or another value is measured by potentiometric sensors. The degree of damper opening level is based on a special program. This digital circuit is hardwired into the ECU, takes into account the filling of the engine cylinders, the turbocharging pressure indicator and the degree of intensity of the USR system in relation to various operating modes of the internal combustion engine.

Euro 6 diesel engines, according to which the nitrogen oxide content in the exhaust should not exceed 0.08 g / km, receive a combined recirculation system. A feature of such a system is two separate lines through which exhaust gases are recirculated. One of the lines of the combined EGR system is a high pressure line, and the other is a low pressure line.

The combined system works similarly to the recirculation system on Euro 5 engines. Additionally, exhaust gases can be supplied from the high pressure line, which is activated in certain operating modes of the power unit. The main task is to reduce the level of nitrogen oxides in the exhaust as much as possible. It should be noted that the exhaust gas cooling radiator in the combined system is absent in relation to the high pressure line.

The main causes of EGR malfunctions

The most common cause of EGR system malfunctions is carbon deposits. Intensive carbon deposits affect the EGR valve seat or plate. Carbon deposits are formed as a result of the operation of internal combustion engines on low-quality fuel. The recirculation system also fails due to malfunctions and malfunctions in the diesel engine power system, incomplete combustion of the fuel-air mixture, deviations in the functioning of the crankcase ventilation system, etc. The EGR system suffers from carbon deposits as a result of mechanical wear of the turbocharger, pistons and cylinders, coking of injector nozzles, as well as various malfunctions in the sensors that transmit signals to the ECU to control the EGR valve.

If the EGR valve is clogged, then it may not work correctly or jam. In the first case, untimely valve operation is noted, which is noticeable in idle mode and does not have obvious symptoms and consequences for the internal combustion engine. In the second case, the EGR valve may stick at the moment of opening or closing. Gasoline units with a stuck valve in the recirculation system are extremely unstable at idle, fuel consumption increases. Diesel engines with an inoperative EGR valve lose power, run rougher and noisier.

To identify faults in the exhaust gas recirculation system, it is necessary to conduct a visual inspection of the condition of pipelines, electrical connectors of sensors and other systems. Advanced diagnostics involves electronic scanning and a series of procedures to check the functionality of the actuators and the EGR valve itself.

It is necessary to check the resistance, as well as the presence of control signals. For this, an oscilloscope and a multimeter are used. If the scan showed that the intake pressure is different from the norm, and there is also an increased air flow, then the valve may be stuck. Replacing the EGR valve in parallel requires a thorough cleaning of the associated lines and connectors, since carbon deposits in the system can lead to the recurrence of faults in the exhaust gas recirculation system after a short period of time.

What is urea used for in a diesel engine exhaust treatment system. The use of AdBlue reagent in the system of liquid cleaning of exhaust gases.

Among the systems of a modern car, there are those that can be safely called environmental. This is, for example, a particulate filter, a catalyst, as well as an EGR system. What is EGR in a diesel engine, what is its use and whether it can be harmful, we will now figure it out.

Schematic representation of the operation of the USR system.

The EGR system, or in other words, the exhaust gas recirculation system (Exhaust Gas Recirculation), is designed to reduce the combustion temperature of the fuel mixture in the cylinders of an automobile engine. In this simple way, the percentage of harmful nitrogen oxides contained in emissions of both gasoline and diesel engines is reduced.

This system is implemented quite simply. A special tube is removed from the exhaust manifold, which is inserted through the valve into the intake manifold. The EGR valve is controlled by the engine's electronic control unit and at the right time delivers a strictly metered portion of exhaust gases to the intake manifold. Thanks to these gases, the combustion temperature of the fuel mixture decreases, which leads to a decrease in the amount of nitrogen oxides in automobile exhaust. It would seem that everything is simple and clear. But this is only at first glance.

Arguments against EGR

Gasket for USR plug (with one hole) and standard (Chevrolet Lacetti).

Despite all the simplicity and apparent usefulness of the EGR system, it is often jammed on gasoline cars and somewhat less often on cars equipped with diesel engines. This practice is especially widespread in our country and other states of the former Soviet Union. And the point here is not only that we treat the environment with a degree of disdain. The problem is that along with the exhaust gases, soot, other solid particles and dirt get into the cylinders of your engine, and all this certainly does not belong there. This problem is especially relevant for our places, where the quality of fuel, especially diesel, leaves much to be desired. To put it simply, the EGR system quietly kills the engine and the diesel engine in the first place. This is due to the peculiarities of our diesel fuel and with a much higher compression in diesel engines and other features of their design.

In addition, the exhaust gas recirculation valve itself often fails. It clogs with the very soot and dirt, it can simply burn out, and replacing this small knot on modern foreign cars is a very, very expensive pleasure.

Well, the last argument against the EGR system, which is typical mainly for diesel engines, is a decrease in average fuel consumption.

Underwater rocks

All of the above can prompt you to immediately look for a familiar craftsman or go to the workshop in order to drown out the EGR system completely and irrevocably. But there is no need to rush here either. Firstly, the EGR valve on different cars is muffled in different ways, and trusting this work to a craftsman from a nearby garage, you must be sure that he will do everything right. Otherwise, you will get errors that you absolutely do not need. In addition, the EGR system in diesel units in winter has its own useful function. It maintains the temperature of the engine in the optimal mode. You are standing at a traffic light or in a traffic jam, and your engine does not cool down. If the EGR valve is muffled, sometimes neither the heater nor some other tricks help. The engine temperature drops, fuel consumption increases, performance decreases. Therefore, it is up to you, of course, to turn off the USR system on diesel engines, but you need to weigh everything very, very well.

Symptoms of EGR problems

On diesel engines, as well as on gasoline ones, there are two main types of EGR system problems. In the first case, the valve does not close, or it burns out and cannot shut off the gas flow, and in the second case, on the contrary, it does not open. It also happens that the tube itself is clogged, and although the valve opens and closes properly, gases do not enter the engine. The control element of the EGR system fails less often, but here it is much more difficult to determine the breakdown.

Problems with the exhaust gas recirculation system are expressed with the following symptoms:

• clicks and knocks;
• engine failures;
• power drop;
• the appearance of errors for no apparent reason;

In the event that you have been diagnosed with some kind of breakdown in the EGR system, you can either repair or change this system completely or some of its components, or shut off the EGR.

There is information that diesel engines with the exhaust gas recirculation system turned off run much longer, precisely due to the fact that less soot, dirt and other indecencies get into them. And some craftsmen have learned to turn off this system for the warm season, and for the winter, when EGR is of serious benefit, they turn it on. And this, albeit in some way, half-hearted decision also has the right to life.

Outcome

The EGR system on diesel engines is slightly less useless than on gasoline engines. It does not provide any real benefit to the car or its owner other than keeping the engine warm during the cold season. At the same time, the operation of this system can be detrimental to the engine, especially if poor quality fuel is used. Silencing the EGR is a decision that should be made after weighing the pros and cons, and this work should be done by a knowledgeable specialist.

Nothing serious with disabling the USR, you will not lose the world ecology either. And the problems may decrease.