They adjust the vacuum to suit the respective engine load state so as to maintain a precisely defined recirculation rate. They are controlled either mechanically or electrically. They perform a similar task to pressure transducers, but are temperature-dependent. Pressure transducers and thermovalves could also be combined.
On account of the high loads it has to withstand, the EGR valve is doubtless the biggest source of faults. Oil mist and soot from the exhaust emissions impede the valve, and the cross section of the valve opening reduces over time until it completely closes up. This causes a steady reduction in the recirculated quantity of exhaust emissions, and this is reflected in the exhaust emission performance. The high thermal loads further facilitate this process. In many cases the hose system for the vacuum is also a cause of faults.
The vacuum required for the EGR valve can be lost due to leaks, meaning the valve no longer opens. If the EGR valve is not working due to a lack of vacuum, this may, of course, also be caused by a faulty pressure transducer or a thermovalve that is not working properly.
There are several ways of checking the exhaust gas recirculation system. Which method you choose depends on whether or not the system is capable of running self-diagnostics. Systems which are not capable of running self-diagnostics can be checked using a multimeter, a manual vacuum pump, and a digital thermometer. However, before you start running complex tests, conduct a visual inspection of all system-related components.
This means checking the following:. If no defects are found during the visual inspection, check the system using other tests and measurements. With the engine switched off, pull off the vacuum line and connect the manual vacuum pump.
Generate a vacuum of around mbar. If the valve is OK, the pressure must not fall within 5 minutes. Repeat the test with the engine running and at operating temperature.
With a pressure differential of approx. If the valve is equipped with a temperature sensor, the sensor can also be checked. To do so, remove the temperature sensor and measure the resistance. The following table lists approximate resistance values for individual temperatures:. Use a heat gun or hot water for heating up. Using the digital thermometer, check the temperature in order to compare the measured values with the reference values.
Valves with vacuum connections that are offset to the side are opened by one connection only. These can be arranged above one another or offset to the side on one level. Valves where the vacuum connections are arranged above one another operate in two stages. The top connection partially opens the valve, and the bottom connection fully opens the valve.
Colour coding is used for marking the connections. The leak tests are performed under the same conditions as for valves with a single diaphragm, but need to be performed at both vacuum connections.
To check the vacuum supply to the valve, the manual vacuum pump can be used as a manometer. It is to be connected to the supply line of the EGR valve. With the engine running, the prevailing vacuum is displayed. On valves with connections arranged above one another, the manual vacuum pump must be connected to the line of the bottom connection; if the connections are offset to the side, it must be connected to the line of the red or black connection. EGR valves on diesel engines can be checked in the same way as for gasoline engines: With the engine switched off, generate a vacuum of around mbar using the manual vacuum pump.
This vacuum must be maintained for 5 minutes and must not drop. You can also conduct a visual inspection. To do so, again generate a vacuum via the vacuum connection using the manual vacuum pump.
Monitor the valve rod the connection between the diaphragm and valve through the openings. It must move smoothly when the manual vacuum pump is actuated. Some EGR valves come with a potentiometer to report back the position of the valve. These EGR valves are checked as described above.
When checking the potentiometer, proceed as follows: Remove the 3-pin connector and measure the total resistance at pin 2 and pin 3 of the potentiometer using a multimeter.
The measured value must be between 1, ohms and 2, ohms. To measure the resistance of the slideway, connect the multimeter to pin 1 and pin 2. Using the manual vacuum pump, slowly open the valve. The measured value should begin at around ohms and increase to 2, ohms. During this check, the manual vacuum pump is not used to generate the vacuum, but instead is used as a manometer. Remove the vacuum hose from the pressure transducer to the EGR valve on the pressure transducer and connect the vacuum pump.
Start the engine and slowly move the pressure transducer linkage. The display on the vacuum pump manometer must change accordingly. The manual vacuum pump is used as a manometer in this case as well. Light-Duty Engines.
The introduction of EGR technology to diesel passenger cars in the s went almost unnoticed and was not considered a major breakthrough for several reasons.
Typical passenger car engines operate mostly at part load conditions where temperatures are relatively low. Heavy-Duty Engines. The wide scale launch of cooled EGR on heavy-duty engines that attracted a lot of attention to the technology took place in late in the North American market. High pressure loop cooled EGR was the most expedient in-cylinder NOx reduction technology that could achieve this emission level []. There was a considerable apprehension in the field regarding the performance, fuel economy, and the durability of these new engines.
While initial statements from fleet managers appeared to praise the new technology [] , some users have complained of the increase in fuel consumption. For EPA , the 0. Navistar—the only manufacturer to temporarily use EGR without aftertreatment for EPA —was able to do so only by certifying engines to 0.
However, the use of EGR was often minimized and in some cases, restricted to certain low load conditions with no EGR used at higher load operating conditions such as highway cruise.
Examples of the later approach are the Volvo D11 and D13 engines launched in that utilized uncooled EGR to control NOx and increase the exhaust temperature for the SCR catalyst at low engine loads. Since the release of the initial Euro VI product lines, systems with over The advantages of eliminating EGR include weight, cost and complexity reduction. On the negative side, SCR-only engines have higher urea consumption and require a larger urea tank.
The on-board diagnostic OBD detection threshold requirements could also be a significant challenge in some markets if very high SCR conversion efficiencies are required to meet regulatory limits—a very small decrease in SCR conversion efficiency would need to be detected. Nonroad Engines. EGR technology was also adopted by nonroad engines.
These engines used high pressure loop cooled EGR and a variable geometry turbocharger. It is interesting to note that the EGR engine used in the John Deere series tractor in had the lowest fuel consumption of all time as determined by the University of Nebraska Tractor Test Laboratory , demonstrating that the fuel economy penalty associated with EGR can be overcome by skillful engine design.
Rough idle can be absolutely caused by EGR, though. Oh, and at full load EGR is also omitted, but at partial load it is in use. So, if the same problem happens at partial load as well, it indicates the cause would be something else than EGR or else you have two separate problems resulting in rough running.
Also consider that the egr motors could be on trying to close the egr if it is seized : a common problem on some cars. Have you checked if it is moving? SolarMike Hmm, it does say in the WSM to check for an initialization click sound from the EGR when starting or stopping the engine: EGR valve initialization is closing action of the valve observed before and after the engine is started, and when the engine is stopped.
I'll need another person for that though. But the main question is if it's showing "ON" during idle is that normal? I did ask if you had checked if it is moving Show 2 more comments. Active Oldest Votes. Improve this answer. Well, I needed two attempts to clean the valve in my car. Maybe if it doesn't close all the way and maybe if it doesn't really, completely seal off the path for the exhaust, you might still get some rough idle. Think of it this way: The better the path for the fresh air good, clean filter; good throttle valve , the less it matters if there is still a small amount of exhaust mixed in.
The mixture is made by the ratio of the pressures of the clean air and the exhaust. What is the definition of warm? Barnes Actually, your question is better than I first thought when I read it.
The dumb answer would be: When your coolant temperature meter shows approx. However, I don't know the value in degrees Add a comment. This is the first time I've heard there's a version of EGR valves being moved by a stepper motor. Until today, I only knew about those being activated by vacuum or a solenoid. Troubleshooting a stepper is a bit more on the tricky side.
As a start: How does the controller know the valve is at one of its end positions? And how do we activate the stepper to check if it is moving?
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