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The exhaust gas re-circulation (EGR) valve recirculates exhaust gas back into the air intake. This means that any unburnt fuel vapour is sent back into the ignition chamber to be detonated again. By doing this your car is reducing the amount of fuel needed in the combustion chamber, giving you better fuel economy, but is also reducing your emissions by taking unburnt from the exhaust system.
As you drive your car the EGR valve will collect carbon particles and oil which will eventually build up into a thick layer of grime reducing the EGR valve’s effectiveness. If it gets too bad it can cause engine management lights to come on, your car’s performance to decrease and it will have an effect on your fuel consumption.
As all cars fitted with the M112 V6 are starting to get on years, I don’t think it’s a bad bit of preventative maintenance to take the EGR valve apart and give it a good clean. It’s tucked down right at the back of the engine compartment though so I must warn you this can get a bit fiddly!
To do this you will need a couple of unusual sockets; an E10 and E12 to be precise. It’s also worth having an 8mm combination to hand too. You’ll also need a EGR valve cleaning spray too. For the M112 you’ll obviously want a petrol specific cleaner such as this Wynn’s article from Amazon:Wynns WY29881 Petrol EGR Cleaner, 150 ml – white
First thing you’ll want to do is remove the airbox cover.
You do this by opening the six metal clips surrounding the cover. There are two on either side and then one at the front and rear of the airbox.
Next, remove the airbox cover from the MAF/intake pipe. There are two more clips to unfold; one at the top and one underneath.
Now the can be removed. The rest of the intake pipe will now have to come off. Firstly, remove the E10 sized bolt. It’s just behind the transmission fluid filler neck.
Now take this rectangular piece of plastic trim off that’s sitting by the intake manifold. Pull it towards the right hand wing/fender of the car and it will pop out of it’s locators. Exactly the same as the engine cover.
The last thing holding that intake pipe in place is a plastic tab. If you reach underneath where the pipe meets the block you’ll be able to feel it. If you push up on it it will release. There is also a rubber vacuum pipe attached to the intake pipe. Give that a pull to take it off.
Now you’ll be able to see the EGR valve itself. This picture was taken when partly removed, but it shows you what it looks like.
When it’s in place you’ll be able to see the pipe leading up the valve from the exhaust and then a second pipe leading away from the valve to the intake.
There are four bolts holding it on, two E12s on the exhaust side and two E10s on the intake side.
The E12s can be found either side of the main pipe. The rearward most one is super easy to get to but the forward one can be a bit of a pain as there’s an air-conditioning pipe and an injector wiring harness right on top of it. I managed to fold the harness out the way but you could unplug it if needed.
Just be sure, if you move the EGR valve at all once the two bolts are undone, to keep an eye on the metal gasket that sits between the valve and the exhaust. Put that somewhere safe!
Once they are removed, follow the pipe leading from the valve to the intake manifold and you’ll find two more E10 bolts holding that pipe to the manifold. Again, one is super easy to get at with a socket and the other is a pain. You’ll find it easier to get the second one off with the enclosed end of an 8mm spanner.
There’s a tiny little 5mm(ish) diameter breather hose under that pipe too. Make sure to pay attention to where that goes before removing it.
All that’s left now to remove is the electrical connector. Just squeeze the two metal clips inwards and it’ll pull right off.
We’ll start by cleaning the exhaust side as that’s the easier bit. Simply flip the valve over and spray any black carbon you can see. The jet from the EGR cleaner spray is quite powerful and it will just lift the carbon off. Keep your face away from where you are spraying though. It bounces back and I can assure you it does not taste nice at all!!
Spray some down the exhaust tube itself too just to get rid of any build up.
The intake side is a lot harder. I’ll talk you through how I did it first but I reckon that there may be a way of making it easier.
I did it simply by wiggling it free. The intake pipe goes into the intake and bends down 90 degrees. It is a fiddle to get out but once it’s out you can spray into it until your hearts content.
You may be able to save some of the wiggling though. At the bottom of that pipe is a big 24mm nut that holds the pipe onto the EGR valve. If you undo that and turn the pipe upside down you’ll be able to spray straight down it without having to take the other end out.
This does however mean your intake will get some of the spray in it along with any carbon it collects along the way. The packaging actually suggests taking the air filter off and just spraying straight into the intake rather than stripping and cleaning it properly. I’m not sure how the car will take any mass of liquid in the air intake though. I’d probably get a second opinion before trying that but I just thought of it as I was writing and thought I’d share haha!
Thanks for reading, I hope you found this useful. It’s one of those jobs that’s really easy on paper but is a bit fiddly due to bolts being in weird places and such. The EGR valve isn’t really an item you service that often though so I can’t hold that against MB. It’s worth doing though, just to free up a bit of airflow.
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By Richard Francis