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what is a egr delete

The EGR system (EGR, AGR) in a car serves to reduce the level of nitrogen oxide emissions. The operation of the system is based on replacing part of the oxygen mixture (air) with an oxygen-free mixture (exhaust gases), thereby reducing the likelihood of nitrogen oxidation in the car’s cylinders. Contrary to the persistent stereotype, no “afterburning” of the exhaust gases occurs, only a decrease in the amount of oxygen in the mixture supplied to the cylinders.


Since the exhaust gases have a high temperature, cooling is required before they are supplied to the cylinders, otherwise the intake mixture will be overheated. To cool the exhaust gases, liquid heat exchangers are used, in which the engine cooling circuit fluid removes excess temperature from the exhaust gases passing through the coolers. Coolers can be with a bypass valve (passes gases past the coolers when the car is not warmed up) and without these valves, with thermostats in the cooling circuit (to turn off the flow of liquid when the car is not warmed up) and without them. Both the bypass valve and the thermostat are designed to speed up the warm-up of the car and start the USR system into operation earlier.

To regulate the amount of mixed exhaust gases, a valve is used, usually an electromagnetic one. The engine control unit controls the valve and at the same time monitors its position through a position sensor, correcting its operation.

Operating conditions of the USR system

To reduce the negative impact of the USR system on the dynamic characteristics of the car, the speed of engine warm-up, and the quality of fuel combustion, the conditions and framework for the operation of the USR system have been established:

The engine has an optimal operating temperature. At low or high temperatures, the USR system turns off or reduces the degree of its participation in mixture formation.

The temperature of the intake air must be within certain limits. At low or high temperatures, the USR system turns off or reduces the degree of its participation in mixture formation.

The USR system is switched off above 3000 rpm.

The USR system turns off or reduces its influence under high loads.

Additional functions performed by the USR valve

The EGR system valve is often assigned two more functions that are not related to reducing nitrogen oxide emissions:

The function of relieving excess pressure in the intake tract during a sharp decrease in engine speed from high load mode. At this point the valve opens for a short time while there is a pressure difference from inlet to outlet.

Burning function of the particulate filter (DPF), if the car is equipped with it. When burning the DPF filter, the throttle valve is closed and the EGR valve is opened slightly to enrich the mixture and allow unburned fuel vapors to reach the particulate filter.

Typical malfunctions of the USR system

As a rule, malfunctions relate to the USR valve and its position sensor, due to which the engine control unit cannot provide accurate control of the flow of exhaust gases to the intake. Starting from EURO-4, malfunctions of the USR system require immediate elimination, since this usually limits engine power.

Typically, malfunctions manifest themselves as follows:

The USR valve is working, the valve position sensor is faulty. The system cannot determine the correct position, but engine performance is not affected. With EURO-3, the car continues to operate normally, with EURO-4, power limitation is activated

The USR valve is faulty, stuck in the closed position. The engine does not deteriorate its characteristics, with EURO-3 you can drive, with EURO-4 the power limit is activated.

The EGR valve is faulty, stuck in the open or slightly open position. The engine runs worse, there may be a loss of power, and excess smoke from the exhaust pipe. With EURO-3, the power limitation mode is not activated; with EURO-4, power limitation is activated.

The EGR system cooler is leaking. Often there are no signs other than a drop in coolant level without visible leaks. Generally not dangerous, but theoretically the leak could be large and cause water hammer in the engine.

Disabling the USR system

In addition to replacing faulty USR system components, you can partially or completely disable the operation of the USR valve.

Positive aspects of disabling the USR system:

When the valve is completely turned off, you can forget about problems with the USR system, this is important for long trips and cars where this system does not work reliably (for example, LR Discovery 3).

Improved response to the gas pedal, reduced delay when starting off and acceleration. This is due to the fact that there is always a maximum of oxygen in the cylinders. When the USR operates, the cylinders are filled with a mixture of air and exhaust gases, and for full performance, several engine revolutions are required to “weather” this mixture.

Disabling the USR system reduces smoke, especially the “spitting” of smoke during acceleration.

Negative aspects of disabling the USR system:

a decrease in the environmental friendliness of the car in terms of nitrogen oxide emissions (but an improvement in smoke!).

disabling the USR system requires the removal of the DPF filter, if the car has one.

Here we'll answer some basic frequently asked questions about removing an EGR system to clear up some misconceptions

QUESTION 1 : Does disabling USR lead to increased cylinder temperature and premature engine wear ?.

ANSWER  1 : More precisely, this is a misunderstanding of the processes in the engine with the USR system. As written above, at high loads, when the maximum temperature occurs in the cylinders, the USR valve must be closed in any case. We can only talk about a slight increase in the “minimum” temperature in the cylinders at minimum engine loads.

QUESTION 2 : Does disabling the USR leads to worse engine warm-up ?.

ANSWER 2 : The practice of many years of using a car with a working USR and a disabled one shows that there is no difference in the speed of warming up the car. As was written above, the USR system practically does not work on a car that is not fully warmed up.

QUESTION 3 : Does disabling the USR leads to disruption of mixture formation and worsens engine operating parameters ?.

ANSWER 3 : Engine management systems are adaptive enough to correctly handle the situation with the USR system disabled. In addition, as described above, there are many conditions for the operation of this system, and in fact it does not always work even in normal mode.


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