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Full Version Will cleaning the EGR Valve improve low end torque

Club XM Forum > C5
I've got an 02 C5 2.0hdi. I bought with low mileage. I presume the previous owner did a lot of pootling in it. I've heard that stop start driving can clog up the valve. Will flushing it improve the low end lorque of the engine?

It seems pretty gutless.
Hi mcmoonter,

Long time no speak. I trust you are well?

The EGR valve simply opens a pipe connecting the exhaust manifold to the inlet manifold thus allowing gases that would otherwise be ejected to the atmosphere by the exhaust to be sent back into the engine to be reburnt. The valve should only be opened by the ECU under particular conditions. Those conditions are really only met when cruising with the engine above, say, 2000rpm (I don't know the C5's programmed rpm). At all other times the valve should be closed.

Clearly, by short circuiting the exhaust to the intake there is a degradation in engine performance since the recycled gases contain much less oxygen for combustion than would fresh air. However, the valve should only be open within a limited rpm window and if you put the foot to the floor and the rpm comes up then the valve should again close. Technically it should therefore only be open when the full engine performance is not required and hence you'd not notice its opening.

That sounds good in principle but of course the devil is in the detail. That's all fine with a new engine which, by definition, has a low quantity of blowpass gases. When the engine gets a bit older more oil and soot is entrained in the exhaust gases and they eventually find their way intot he intake manifold. If you've ever stripped an intake manifold on a car with EGR then you will find it coated in black tar. The presence of the tar reduces the internal diameter of the intake manifold and also increases the surface roughness thereby increasing the friction. The end result is a reduction in the quantity of air which can be drawn into the engine. This in turn will affect its performance.

My father owned an Audi A6 which ran very sluggishly for most of the earlier years he owned it. It also had tremendous difficulty starting. Having checked out all the obvious factors he was at his wits end when he decided to remove the RGR valve from the car. When he inspected it he found that the disc in the valve which blocks off the flow of exhaust gases was mostly worn away leaving most of the port open even when the valve should be closed. He cut a piece of tin out of a fizzy drink can and placed it between the mating flanges of the EGR and manifold to blank off the gases all together. The result was an astounding improvement in performance, strating and fuel economy. this lasted a couple of years until the symptoms returned. Knowing the EGR was blanked off he did not look there first for the fault believing the blank still to be in place. Having exhausted all other avenues without success he removed the EGR valve again. He found that the original tin blank had worn through and again was allowing exhaust gases to pass even when the valve was closed. This time he blanked it with a bit more substantial material and the problem did not return.

If there's no other reason for the engine to be sluggish it might be worth taking the EGR off the car and inspecting it. At the same time it might also be useful to establish the condition of the intake manifold. It may indeed be internally coated with tar affecting the engine's ability to breathe.

The concept of the Exhaust Gas Recycling appears sound when dealing with a new engine. It probably will indeed reduce the emissions by reburning exhaust gases. However, that theory breaks down as the car gets older. The tarring up of the intake manifold and the prospect of EGR valve failure has the opposite effect and increases overall emissions. Thus, in the long term, the planet is worse off for the presence of the EGR ideology. Now where have we heard that before? Unleaded petrol anyone?

If you want, I can plug your C5 into the laptop to make sure there's nothing else amiss with the engine management system. Let me know if that's any use to you.


noz cool.gif
Cheers Noz

Yep all is well. I say well...... Yesterday I tripped carrying a non running chainsaw and took a chunck out of my shin. Spent the evening in A&E. Paper stitches and a big bandage. Feeling better after the mother of all whiteys.

I'll give the valve a clean out. If there is no noticeable performance improvement, I may take you up re a laptop diagnosis. May be air mass meter or some other thing.

The air mass meter gave up on my old Passat. The difference when fitting a new one was like a new car.

Ouch, as you say.

I have to admit a similar faux pas of my own. Around easter time I tried to cut my hand off with an axe. Just about managed it too. Strange to see what it looks like from inside when its your own. I don't think I'll be doing that again in a hurry.

You're right about the Mass Air Flow meter. They are notorious. Let me know if you need the laptop.


noz cool.gif
They both sound nasty accidents. I could join in but think it best not to.

If you need a replacement MAF be careful where it's purchased from, I'm told by several reliable sources there's alot of fake ones out there that don't work properly.

Other possibilities are faulty vacuum solenoid valves or leaking vacuum pipe.

Hi Steve,

Sorry, I had not intended to create a thread of self-harming anecdotes. The real thing was bad enough. A 'whitey' as mcmoonter calls it biggrin.gif (very accurate description)

I've heard that before about MAFs. I just wonder if my own current, mild, woes have any bearing on the MAF condition.....another thread I think.

The EGR valve itself is 'normally-closed'. i.e. with any failure of any kind upstream of the valve will cause the valve to adopt its default condition of closed. The exception to this would be if the solenoid valve controlling the vacuum had jammed in the 'open' position even with the power off. That would allow the vacuum through from the pump to the EGR valve even when it was supposed to be off. The engine performance is degraded when the EGR valve is open rather than closed. Any fault causing it not to open will not be experienced by the driver. Any fault causing it to be open when it shouldn't be open will manifest itself in poor engine performance.


noz cool.gif
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