The subject of EGR (Exhaust Gas Recirculation) systems comes up often so I thought it was about time we explained further on how a dirty EGR can effect performance, MPG and exhaust emissions.
With our professional range of cleaners we are confident that we can resolve a large percentage of the minor poor running issues (hesitation, poor idle, reduced performance, MPG, increased exhaust smoke etc) that our customers encounter. So where does that leave the other percentage? From our experience, faulty EGR’s (due to deposit accumulation) and faulty sensors (the Mass Airflow being the most common) contribute to a large proportion of running issues that professional fuel injector cleaners won’t resolve.
What is an EGR valve?
An EGR valve, or exhaust gas recirculation system is a primary component of an engine’s emissions system on both petrol and diesel powered vehicles. Its purpose is to reduce NOx emissions by recycling a proportion of the combustion gases that normally exit through the exhaust. Recirculating some of the spent exhaust gases back into the engine is one way to reduce these harmful emissions, and this is done by way of an Exhaust Recirculation System (EGR). The main component of this system is a valve that essentially returns a proportion of the exhaust gases back into the engine to be mixed with clean air, fuel and then re-combusted.
The gas to be recirculated can be passed through an air or water type EGR Cooler. This in turn reduces the temperature of the gas, which reduces the charge temperature that leads to an improved quality of combustion and engine power. In the case of a diesel engine, the recirculated proportion of gases can sometimes be as high as 50% under certain operating conditions.
Over time the EGR valve and associated pipework accumulate carbon deposits. These inhibit bypassed exhaust gasses back into the intake and play havoc with the fuelling and thus we end up with hesitation, reduced MPG and ironically, excessive emissions, particularly when the EGR is transitioning from open to close and vice versa. Unfortunately modern electronics do not always recognise a faulty EGR except when flow is fully impeded or there is an electronic fault with the control solenoid/actuator. What happens is that carbon builds up on the EGR valve itself creating a resistance to the opening and closing of the valve. Basically, this vacuum operated valve sticks and the solenoid that operates the vacuum has to work overtime to create sufficient vacuum to open the valve. An excess draw of current then trips the ECU warning light.
Carbon build-up cannot be avoided fully as there is a natural and strong affinity between hydrocarbons and metal surfaces. The key is to maintain a manageable level of carbon build-up within the system and in quantities that the engine can naturally consume.
It is important to understand why carbon builds up in the first place and where it comes from. Contrary to popular believe, carbon build-up comes not just from fuel but also from the engine oil. Engine oil can bypass engine rings, inlets valves and crankcase breather systems and then polymerise on intake and emission control system components as its recirculated. This creates a porous surface from which further oil vapour and then also excess hydrocarbons produced from the combustion process can then adhere and create further build-up.
There are numerous solutions now available ranging from aerosol sprays with accompanying fuel cleaner to pressurised detergents that are atomised into the intake and EGR system. The most effective way is a manual clean of the EGR valve and periphery pipework but this is not always possible without significant labour time. It is also important to note that it is not always the valve that blocks up but the pipe leading from the EGR back into the intake. The hole(s) where it leads into the intake are normally very small and can block up very easily. This then backs up to the valve.
Why do fuel cleaners struggle with EGR cleaning?
Fuel cleaning technology has come on a long way and carbon can be removed from most areas of an engine and emissions control system though fuel system cleaners. However, EGR’s are notoriously difficult with this method. Here’s why:
There are 4 types of fuel based EGR cleaners (1st 3 are added to the fuel).
1. Low-cost solvent based cleaners that do very little other than clean the fuel injectors as the chemistry is destroyed during the combustion process.
2. Higher quality fuel system cleaners that use chemistries such as polyether amines to help remove combustion and post combustion deposits, although most of it Is destroyed during the combustion process.
3. Patented molecules that are activated during the combustion process (rather than destroyed) and are then carried in the recirculating gases. These molecules bond with the carbon acting as a catalyst for its removal.
4. Solvent cleaners that are sprayed into the air intake and circulate through the intake system, EGR, combustion area and out into the post combustion areas including the turbo and EGR again.
Product type 1 is useless. Product type 2 may have some effect if the carbons are mainly fuel related, but this process relies on heat. What happens is that such products improve the quality of the combustion to the degree that the cleaner exhaust gases will naturally scavenge and remove carbon from post combustion areas. This is more workable in areas such as the turbo, DPF, CAT etc as heat is maintained. This cleaning mechanism is effective with HOT, clean exhaust gases but an EGR system is designed to cool the gases so the efficacy is reduced considerably. Furthermore, there has to be sufficient flow through the EGR system for this process to work. If it is blocked completely then natural scavenging will not work.
On a side note, fuel additive manufactures have been careful not to reveal the fact that combustion modification and improvement and the resulting cleaner exhaust gases can naturally remove carbon deposits! I remember one of our long term test vehicles (Audi S8 4.2 TDI) having exhaust tips cleaner on the inside than on the outside and I’m not kidding.
Product type 3 is similar to 2 and slightly more effective. Specific molecules in the fuel additive are dormant and become active during the combustion process. Carried through the recirculating exhaust gases they bond to carbonaceous deposits. This acts as a catalyst to dissolve/remove the deposits to the combustion area where they are then burned. However, just like with product type 2, this method requires sufficient heat and airflow through the EGR system.
Product type 4 is the most effective as the solvents do not require heat to work and and hit the target areas more easily. Again, if there is substantial oil build-up then it is much more difficult to remove.
For information on products to clean the EGR system and keep it clean, read our article HERE.