TDI EGR system FAQ (for all model years of TDI)
Table of contents
Where is the EGR and what does it do?
Checking proper operation of the EGR valve.
Removing or cleaning the EGR system/intake manifold.
How do people modify it and why?
Why I do not recommend removing the EGR system.
The future of the EGR system.
Where is the EGR and what does it do?
EGR stands for Exhaust Gas Recirculation. The system is located on the firewall side (rear) of the engine on almost all TDI engines. It reduces NOx emissions.
The 1997-2003 1.9L TDI systems take in exhaust gas at the exhaust manifold, sends it through the EGR cooler (except North American market 1996 passat), and then puts it into the intake manifold through the EGR valve at the intake manifold. The 2004-2006 EGR system takes in gas at the exhaust manifold, sends it through a diverter valve, then the EGR cooler, then through the EGR/diverter valve into the intake manifold. These later cars used an electronic EGR, earlier cars used a vacuum and solenoid operated EGR. These are standard routings in most cars, both diesel and gasoline, turbo and non turbo.
The purpose of the EGR system is to reduce emissions. By mixing exhaust air back into the engine, it lowers peak combustion temperatures under partial load and reduces NOx emissions anywhere from 50%-75%. The reason why putting exhaust gas (hotter than ambient air) into the intake stream reduces NOx is because the free oxygen would otherwise turn into NOx. Because a diesel runs very lean (efficient), there's also considerably more oxygen in the exhaust vs. a gasoline engine which would otherwise turn into NOx emissions during combustion. The MAF air intake sensor also sees a reduction in air intake and adjusts fueling. Everything else being equal and within limits, in a diesel, more fuel = more power = higher temperatures. In a gasoline car, more fuel at the right ratios = lower temperatures.
The system is regulated by the car's computer to open or close to varying degrees depending on load and other factors. At light load or idle, up to 30% of the intake air flow can be exhaust. At heavier loads, the EGR valve begins to close and at a certain point, the car's computer closes the EGR valve completely. In the newest TDI engines (2009+), the EGR actually opens all the way during a particulate filter regeneration cycle. Since the EGR is opened and closed at various engine loads, the presence or absence of the EGR does not have a significant effect on engine longevity. In theory, it lowers temperatures at lighter loads where there is less fueling and lower cylinder temperatures. In most cars, at heavy loads with more fueling and higher temperatures, the EGR system is closed so it does not reduce peak power at all.
Before going into the engine, exhaust gasses normally pass through a cooler. A side benefit of an EGR cooler is faster engine warm up because the hot exhaust gasses give their heat to the coolant. This is great for a diesel because most engine wear, worst fuel economy, and emissions, occur on a cold engine. Diesels have a lot of piston blowby and once the engine is warmed up, the engine seals tighter and gets better fuel economy.
In the mk3 jetta and passat, the EGR is part of the intake manifold. EGR metering is a calculated value by the car's computer. In the mk4 and pumpe duse mk5 cars, the EGR is a separate unit bolted to the intake manifold and can be replaced as a separate unit if necessary. These cars also note how much fresh air is coming in from the MAF to determine how the EGR is working. This is why blocking off the EGR on these cars can cause a check engine light/malfunction indicator light.
The introduction of the pumpe duse engine in 2004 also saw the addition of an O2 sensor in the exhaust. Unlike O2 sensors in gasoline cars, the TDI sensor is not used to change the amount of fuel injected. Again, it does not directly control fuel metering. The TDI O2 sensor is used to calculate the potential for NOx formation and regulate the EGR valve with more precision, resulting in cleaner emissions.
Here is a picture of a pumpe duse diverter valve and EGR cooler. More
pictures can be found in 1000q:
A5 pumpe
duse EGR removal.
Here is a picture of a non pumpe duse EGR and EGR cooler and the routing (as
viewed from the back of the head) from the exhaust manifold, through the cooler,
and to the intake. More pictures can be found in the 1000q:
a4 egr cleaning and removal writeup. If you have an mk3,
see 1000q: mk3 intake and egr
removal.
The 2009 Jetta TDI diesel has a much more complicated EGR system. It shouldn't require cleaning because it's partially filtered. It uses a high and low pressure side and a backpressure valve in the exhaust. It's too new to know long term reliability but it should be relatively maintenance free compared to the earlier car's soot buildup. Some believe that the EGR tuning is the cause of occasional engine stuttering when at partial loads.
Checking proper operation of the EGR valve
The system is normally controlled by the car computer and a solenoid. The solenoid controls vacuum to the EGR valve. The mk3 and mk4 early ALH engine cars use a spring loaded valve that moves up and down. The mk4 later pumpe and mk5 cars use an electronic rotating diverter valve type EGR. This is less suspect to clogging than a spring type.
To check for the valve proper operation, with the car off, remove the intake piping before the intake manifold to see the EGR valve. Take a look inside. If you see a lot of carbon buildup, the intake manifold will need cleaning. A little buildup of a 2-3 millimeters is normal and does not require cleaning.
For the cars that use a spring loaded valve, remove the vacuum line on the EGR valve and apply suction with a vacuum pump. Don't try sucking with your mouth since there isn't enough force and the hose is dirty. The valve should move towards the vacuum diaphragm when you apply suction. Since it's spring loaded, it should return to closed when you release suction. If it fails to fully close, it means that there's a problem.
EGR valves that are electrically operated have sensors to show their position and should trip an error code in the car's computer.
If the EGR valve works but the system still doesn't work, check the solenoid, electrical connectors, and wiring. A vacuum leak can cause malfunction of the EGR valve. A clogged line can also cause malfunction. If none of these solve your problem, then the computer (ECU or ECM) or other sensor may be faulty.
Removing or cleaning the EGR system and intake manifold
If there is excessive carbon buildup on the intake manifold and EGR, it must be removed and cleaned. There is no set time, mileage, or factory recommendation on when to clean it since accumulation can vary according to type of engine oil used, driving style, quality of fuel used (ultra low sulfur diesel, biodiesel, etc.), and even by car. The reason why VW diesels seem to be more prone to buildup than other cars is probably due to engine oil mist in the intake system meeting the recirculated exhaust gases. The oil mist comes from the CCV (Crank Case Ventilation, similar to a PVC system) system.
The main component of the CCV system is on top of the valve cover and looks like a black plastic hockey puck with a hose. Diesel cars naturally have more piston blowby than gasoline engines which pressurizes the engine crankcase. You must vent out the pressure or else it could blow out an oil seal. The CCV hose is attached to the intake piping before the turbocharger so that crankcase vapors are drawn out of the engine crankcase. There may be a heating element on the hose. (This is also why it's normal for a little bit of oil in the intercooler to be present - however, excess oil could indicate a problem.) The soot from the exhaust and oil mist combine to form the carbon buildup. Again, quality of fuel (biodiesel or ultra low sulfur diesel), engine oil, EGR system operation, and driving style all contribute to carbon buildup which must be cleaned. Since the introduction of ultra low sulfur diesel in the US, the likelihood of severe intake manifold buildup has reduced.
To clean the system, it's best to remove the entire intake manifold and EGR system but you can get away with just cleaning the intake manifold, EGR cooler, and EGR valve. You MUST remove the components from the engine when cleaning them. Do not clean them on the car or use de-carbonizing chemicals to clean the intake manifold. If a large piece of carbon breaks off and gets stuck in a valve or turbo, it will result in severe engine damage! The liquid or solids can also go into a cylinder and cause hydrolock. Dealers used to do "on car cleaning" until they realized that some engines were damaged from this. If you didn't get the message - you must remove the parts from the car to clean them! Remember that the pistons are almost touching the cylinders in a diesel engine due to the high compression, so a stuck valve or small amount of standing liquid may cause engine damage.
You can also just replace them with new parts instead of cleaning them. It is recommended for the mk3 cars to replace the intake manifold because the EGR valve can malfunction and leak oil and is not removable from the intake manifold. On the mk4 and mk5 cars, you can reuse the manifold since it's just a cast piece of metal and the EGR can be replaced as a separate unit as needed. Ccleaning them is a very dirty process so wear clothes that you don't mind getting dirty.
See 1000q: mk3 intake/egr removal and cleaning (1996-1999 TDI)
1000q: mk4 intake
manifold/EGR removal and cleaning (1998-2005 TDI)
1000q: mk5 pumpe duse intake
manifold/EGR removal and cleaning (2005.5-2006 TDI)
1000q: mk4 B5 Passat intake
manifold cleaning (2004-2005 TDI)
Another problem for the mk3 and mk4 TDI is leaking oil out of the EGR weep hole. The EGR has a diaphragm inside that moves on a shaft. The other side is vented to the atmosphere. As the shaft wears, it can leak oil that comes out the weep hole. You don't want to plug the hole or else the EGR will not function correctly. The mk4 EGR is removable from the intake manifold. If it weeps oil, replacement is suggested. The mk3 EGR is not removable from the intake manifold. If it weeps oil, you could replace the entire intake manifold or reroute the weep hole by running a small hose from the hole to into the intake tubing upstream of the turbo or onto the ground or a catchcan.
How do people modify it and why?
People remove the EGR system for two main reasons. Removing intake restrictions will reduce pumping losses and create more available power. Removing the EGR will also greatly reduce the amount of buildup that you will see on the intake manifold. It's important to not seal off the crankcase ventilation hoses because the crankcase builds pressure that must be vented! Some people vent the hoses into a catchcan. Do not vent the hose onto the ground because you'll have an oil slick under the car and on the road. This is like dumping used oil onto the road which contaminates the ground/groundwater.
There are a few ways to modify the operation of the EGR system. The first is to use the adaptation function of a vag-com cable to adjust the degree of EGR system operation. The computer may react to the change in EGR flow and adjust timing. People report a mileage loss with this method of adaptation. It is possible to shut it off completely with a Ross tech VCDS but this may set a check engine light.
The other way is to physically remove the EGR valve and/or entire system from the car and replace one end with a block off plate and the other end with a straight pipe (race pipe). The issues surrounding total removal are slightly different in the mk4 and mk4 pumpe duse and mk5 cars. The problem is that it will set off a check engine light unless you cover it up in the mk4 non pumpe duse cars and it also removes the anti shudder valve. The anti shudder valve is the first thing that might stop a diesel engine runaway (a type of malfunction) and could save your engine from being damaged. See 1000q: turbocharging - diesel engine runaway for more details on an engine runaway. If it's a bad runaway then it won't stop it since it's closure is too short but it's still better than nothing.
With the mk4 pumpe duse and mk5 cars, will definitely set a check engine light that is much harder to get rid of. These cars use an electronic throttle plate and will cut off air flow to the engine, stalling it, if the computer doesn't see enough EGR flow. There are chips out there that can disable the check engine light, contact chip tuners for more details.
Here is an example of block off plates for mk4 and mk5 TDI. One plate
has been tapped for an exhaust gas temperature probe, pic by burpod. You
could also make an EGR restrictor. It's the same as a block off plate but
it has a hole drilled in it to just restrict flow instead of completely blocking
it off. This will reduce how often the check engine light will come off
but you'll probably still get it.
Why I do not recommend removing the EGR system
First, it is an emission device. It cost the manufacturer money to design and put it on your car. They did it for a reason, and that reason was to meet emissions standards. Emissions controls are in place because even if you don't believe that vehicle emissions contribute at least somewhat to global warming, they make the air cleaner to breathe for you, your neighbors, and the people who are on the street such as commuters, police, and road crews. In countries that have poor emissions controls and poor air quality, greater emissions strongly contribute to shorter lives and develop more diseases to people who are regularly exposed to vehicle exhaust. Since most TDIs are daily drivers, making changes to emissions devices has a much greater effect vs. special use (like off road race cars) or weekend cars. Here are some more facts to consider.
If you are thinking of removing the EGR cooler only so that the intake charge is hotter and in theory, less prone to carbon buildup, this defeats a large portion of EGR effectiveness since emissions and temperatures will be higher without the cooler. The EGR cooler also helps warm up the engine by giving heat from the exhaust to the engine. This results in a faster warm up, less engine wear, and better fuel economy due to the faster warm up.
Removal of the EGR can also set off a check engine light which will result in an automatic failure during emissions testing and will prevent you from registering the vehicle in many states. Disabling the light or taping over it won't work since they plug in an obd2 scanner which reads your car's computer. There are ways to trick the computer into not showing a check engine light like through your chip tuner, but tampering with emissions devices may be illegal where you live.
The biggest gain is reduced cleaning of the intake manifold. This is not much of a gain anymore because the new ultra low sulfur fuel used in all US and Canadian diesel fuel has reduced clogging. Biodiesel users report no excess intake buildup although there'll always be a small film. There are only small mileage or power gains from disabling the EGR system since it only operates at partial throttle. At full throttle, the EGR system is closed by the computer so it makes no noticeable difference in peak power. If you are removing the EGR for reduced pumping losses and the small power or economy gains, bigger and better gains can be made elsewhere. See 1000q: basic performance upgrades for a list of starting performance mods. Also, the pumpe duse cars use an O2 sensor to regulate the EGR system much more efficiently than non pumpe duse cars. Even newer technologies on the common rail system cars allow more precise fuel delivery and burn, resulting in less intake clogging.
I have seen comments that suggest the ingestion of the sooty EGR exhaust gasses combined with diesel piston blowby can cause oil contamination. This is false since the soot gets burned in the combustion chamber. Diesel engine oil is also formulated to hold soot from any blow by and you would have sooty oil whether you have an EGR system or not. Engine oil quality and engine maintenance is a much greater factor in proper lubrication than the presence of an EGR system.
One final thing to consider when modifying the EGR system: if you modify or delete the EGR system, you will almost certainly have problems getting warranty coverage on the engine. Even though it should not damage the engine, VW will probably claim that you caused the damage. If you wanted to pursue it, you would have to hire attorneys to take any further action and it's not economical to do so. It would be hard to deny a claim on the suspension if you modified the engine, but be prepared to encounter resistance if you make any claim on a modified engine. If your car is under warranty, I do not suggest making an EGR change unless you are prepared to change it back when you go to the dealer. Modifications like an ecu chip or larger nozzles are not easily detected and most dealership mechanics would never find them but a missing or blocked EGR can easily seen.
The EGR system is an emissions device and because it makes such a drastic difference in emissions, it is unlikely that it will go away soon in diesel cars. While some gasoline cars have eliminated the EGR, they can also run tighter air/fuel ratios, something that would never be possible with a diesel engine. This is partly because a diesel isn't throttled the same way a gasoline engine is, and because it runs very lean/efficient (much more air than fuel). The clogging problem that older cars have doesn't seem occur on newer cars as much for a number of reasons: ultra low sulfur fuel, more precise fuel delivery and burn, and new EGR systems all reduce the likelihood of clogging. Some diesel trucks use a mini catalyst before the EGR to catch and burn up any soot, preventing most of it from entering the intake. Some gasoline cars no longer use EGR systems but because of stricter emissions standards and because of diesel engine needs, this does not appear to be possible for diesel cars anytime soon.
Some people criticized catalytic converters for killing the 1970's muscle car, but the truth is that poor engineering and changing times killed the muscle car. And today, cars are far more powerful, efficient, and cleaner then ever.
Do you know something that should be added or corrected in this article? Post your comments in the myturbodiesel.com forums