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Old 3rd December 2007, 14:04   #1
Jules
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Default More on the EGR Bypass Valve....Modify or Leave alone

Just been reading an article on Honest John an excellent review Website:
http://www.honestjohn.co.uk/carbycar/
See also
http://www.honestjohn.co.uk/carbycar/index.htm?md=121&

This is admittedly about a Ford Galaxy 1.9Tdi, but I wonder if this would apply to 75 ZT owners who have disabled their EGR or fitted a bypass.

The consequences can be dire...............read on

"On TDIs, EGR valve should open to allow carbon dioxide, which acts as a cooling gas) into the combustion chambers when the engine is under load (>30% boost). This allows the combustion chamber temperature to drop and thus the temperature of the exhaust gases. If it sticks in the closed position the exhaust gas temperature will rise causing a) the turbo bearings to fail and b) engine oil into the induction system. This can cause the engine to run on its crankcase oil until it is either stalled or goes bang. Problems with EGR valves in TDI engines are often the cause of rough running when the valve is stuck in the open position as well. In several cases turbos have blown but the EGR valve has not been replaced. Inevitably the new turbo unit will not last long."

Come on technical bods, lets have some more clarification on this subject!

Left:............................................. ..........Right
choked EGR 40k miles.................................EGR Bypass Tube
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Last edited by Jules; 17th January 2008 at 13:26..
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Old 3rd December 2007, 14:24   #2
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oooer! Dunno, but after 10,000 miles I have found no problems...

lets hope my Mobil 1 every 7500 miles keeps dem bearings happy

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Old 3rd December 2007, 15:26   #3
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The whole statement seems to have a lot of flaws:

1. How can exhaust gasses (that the Egr lets in to the manifold) be cooler than the intake air?

2."On TDIs, EGR valve should open to allow carbon dioxide, which acts as a cooling gas) into the combustion chambers when the engine is under load (>30% boost)."
The whole idea of the Egr is to recirculate some of the exhaust gasses that are more likely to have a higher concentration of unburned fuel.(If you've ever tried to open an egr, it takes a lot of vacumn!)
Eg. on the over-run or if you accelerate too harshly.(throttle opening more than engine can draw in)

3."This can cause the engine to run on its crankcase oil until it is either stalled or goes bang." Of course a engine runs on its crankcase oil what other oil would it use!!!!
Unless he means the oil from the failed turbo bearings entering the induction system and being burnt, but that wouldn't cause your engine to go bang.
If it was that bad then the engine wouldn't run as the ECU would find it difficult to cope.
The Police would have stopped you way before then, for the amount of smoke you would be pumping out of the exhaust. I've had major bearing falure on a turbo and believe me you'd know about it!

4. Exhaust gasses reaching a temperature that would lead to failure of the turbo bearings. What's he running his diesels on???


The only part of this statement I agree with is that, an egr that is stuck partially open will cause rough running of the engine.


Does this guy know what he's talking about? I doubt it.

Egr bypasses make the engine more efficiant by increasing the amount of air that is entering the engine. It won't cause any of the problems described above. If I thought it would have any detrimental effect I certainly wouldn't have fitted one!


Russ

Last edited by BigRuss; 3rd December 2007 at 15:31.. Reason: spelling
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Old 3rd December 2007, 16:23   #4
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I must admit other than give it a clean this is a mod that I haven't done on my car. I was hoping to see some dyno evidence that it was worth while first.

What I can say is if you open the egr valve via testbook with the engine running at slow speed it causes very noticeable rough running and does a pretty good impression of a duff maf performance wise, hence why I guess it is only designed to open at high speed where the performance impact is reduced and I believe it is its role to reduce emissions that it is there for rather than any other reason.

One of our members came over a couple of weeks ago and his egr gave all the symptoms of sticking open although testing it via Testbook suggests it was not as it would then close and open on demand without delay

The effect on his car was basically rev it up valve opens let the engine tick over and valve seems to take quite a while to close again so until it did the car ran badly. What was not clear was whether the ECU was keeping it open or if it was faulty, even weirder repeating the exercise on my car once fully warmed up showed my valve was not even being opened in the same way I semi wondered at the time if my ECU does actually open it at all and if so the bypass mod would be pointless!

I assume the vacuum pump opens it and some from of internal spring closes it, I wonder if the spring failed could the exhaust gas pressure force and keep it open for a while?

Certainly in his case blanking it off or fitting a bypass may be worthwhile

Anyone cut one up to see how the valve operates and check what sort of gas seal they have when closed?
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Old 3rd December 2007, 16:41   #5
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Quote:
Originally Posted by bigruss42 View Post
The whole statement seems to have a lot of flaws:
2."On TDIs, EGR valve should open to allow carbon dioxide, which acts as a cooling gas) into the combustion chambers when the engine is under load (>30% boost)."
Russ
Hi
I understood that the EGR valve opened when engine was only under light load,
ie it would'nt be getting nearly as hot as when engine is having to work hard in everyday running conditions anyway.
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Old 3rd December 2007, 17:46   #6
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Quote:
Originally Posted by baxlin View Post
This was discussed on here in August this year, suffice to say Ron's reply put my mind at rest, ie it seems to be scaremongering, and is not correct.

malcolm
I don't know who wrote the text but I would say there is some very accurate data on the HonestJohn website as it comes from Manufacturers, Main dealers, Garages & Breakdown Recovery companies.
Oh well at least 260's don't have an EGR to worry about:lol:
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Old 3rd December 2007, 19:08   #7
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Quote:
Originally Posted by simpsora View Post
Hi
I understood that the EGR valve opened when engine was only under light load,
ie it would'nt be getting nearly as hot as when engine is having to work hard in everyday running conditions anyway.
That's what I said in the next couple of sentences. I didn't write the bit in the quotation marks.


The Egr valve has a hefty spring in it. When I removed mine I left it to soak overnight in some Gunk and then removed the gunge with a toothbrush.
It cleaned up as new.
I thought I'd check to see if was operating properly and hadn't siezed. so I inserted a piece of copper pipe in the exhaust gas inlet of the Egr and pressed. Didn't move a millimetre!! found that to move it required me to put most of my wieght on to it before it would budge, but wasn't sticking at all.
God knows how much vac. you need to open it?

The Intake mod lets the engine breathe better, but if you dont put in the egr bypass the air is hitting an equal reduction in size later, making the intake mod on its own limited in it's effectiveness, if not pointless IMHO.


Russ
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Old 3rd December 2007, 20:24   #8
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Default So Much Garbage

I have never heard so much garbage talked on this forum about the EGR valve. I am so suprised that droves of R75 lemings are heading for the cliffs, based on half truths and miss-information, to the extent that they are removing a crucial bit of automotive design, in the mistaken belief it is costing them a few HP.

There seems to be this idea that the introduction of a small percentaqe of exhaust gases into the inducted air is going to increase the air temperature and not cool it, as Honest John & others have suggested.

IT HAS NOTHING TO DO WITH AIR INTAKE TEMEPERATURE!

IT HAS ALL TO DO WITH COMBUSTION TEMPERATURES - IN THE CYLINDER!

It is a great pity the majority of forumites do not understand the chemistry of combustion in a diesel engine.

The fuel takes as much oxygen as it needs. At low revs there is a surplus of oxygen, such that the flame temperature starts increasing as the fuel/air mix gets more diluted. Ultimately, this produces Nitrogen Oxides (NOX), which are not only toxic , but are bad for the environment.

The introduction of exhaust gases, which are low in oxgen, dilute the oxygen in the cylinder, thus reducing the combustion temperatures.

The suggestion that turbo bearings etc can be affected by these increased temperatures is perfectly valid. Even exhaust valves could be at risk.

People have suggested that disabling the EGR doesn't affect the MOT emmisions. This is only because they are done at max revs, where most of the oxygen gets used up correctly, so it is low in NOX's

The other misconception is when the EGR valve actually operates. It is supposed to be closed at idle, otherwise there can be erratic idling, which I'm sure a few suffer from.
However under full acceleration (wide open throttle), it should NOT be open also. At cruising where the engine is operating more effeciently then the valve should open, as controlled by the ECU.

So it is quite possible that by removing the EGR, cruising fuel consumption could be compromised.

So why many people are prepared to pay good money for EGR by-pass tubes , for the sake of an indeterminate increaser in power is beyond me. Although I will accept that at wide open throttle, then the marginal restriction could lose a few HP- big deal.

Leave well alone, but clean reguarly.

Colin
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Old 3rd December 2007, 22:25   #9
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Quote:
Originally Posted by ColinW View Post
I have never heard so much garbage talked on this forum about the EGR valve. I am so suprised that droves of R75 lemings are heading for the cliffs, based on half truths and miss-information, to the extent that they are removing a crucial bit of automotive design, in the mistaken belief it is costing them a few HP.

There seems to be this idea that the introduction of a small percentaqe of exhaust gases into the inducted air is going to increase the air temperature and not cool it, as Honest John & others have suggested.

IT HAS NOTHING TO DO WITH AIR INTAKE TEMEPERATURE!

IT HAS ALL TO DO WITH COMBUSTION TEMPERATURES - IN THE CYLINDER!

It is a great pity the majority of forumites do not understand the chemistry of combustion in a diesel engine.

The fuel takes as much oxygen as it needs. At low revs there is a surplus of oxygen, such that the flame temperature starts increasing as the fuel/air mix gets more diluted. Ultimately, this produces Nitrogen Oxides (NOX), which are not only toxic , but are bad for the environment.

The introduction of exhaust gases, which are low in oxgen, dilute the oxygen in the cylinder, thus reducing the combustion temperatures.

The suggestion that turbo bearings etc can be affected by these increased temperatures is perfectly valid. Even exhaust valves could be at risk.

People have suggested that disabling the EGR doesn't affect the MOT emmisions. This is only because they are done at max revs, where most of the oxygen gets used up correctly, so it is low in NOX's

The other misconception is when the EGR valve actually operates. It is supposed to be closed at idle, otherwise there can be erratic idling, which I'm sure a few suffer from.
However under full acceleration (wide open throttle), it should NOT be open also. At cruising where the engine is operating more effeciently then the valve should open, as controlled by the ECU.

So it is quite possible that by removing the EGR, cruising fuel consumption could be compromised.

So why many people are prepared to pay good money for EGR by-pass tubes , for the sake of an indeterminate increaser in power is beyond me. Although I will accept that at wide open throttle, then the marginal restriction could lose a few HP- big deal.

Leave well alone, but clean reguarly.

Colin
Cheers Colin for such an in depth knowledgable reply. Thank god I have not done this mod. No doubt someone will have a different opinion whos knowledge is greater than B**'s and Rovers technical gurus. BTW I will change my opinion if someone convinces me otherwise.
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Old 3rd December 2007, 22:38   #10
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Nearly 40% of the air intake area is a marginal restriction?

NOX emissions are not part of the MOT test on diesel vehicles it is purely a smoke test.(but by the way my tester stated that mine had the cleanest emissions he'd seen in along time)

Fact: Egr systems reduce NOX emissions at the expense of power and fuel ecomony.
They are there to try and reduce emissions, they are not essential for the running of the engine.
There are probably more harmful emissions caused by a malfuntioning valve (which is probably quite common) and poor servicing and maintenance, than the possible small increase in the use of the bypass. After all only 6-10% of the exhaust gases are recirculated the rest goes out of the tailpipe.

The cleanest engines are those that use fuel and air in the correct mix at the right time to enable complete combustion.
Many people who have fitted the bypass have also fitted one of Ron's tuning boxes, so the engine is not in it's original state of tune.
It would be interesting to know the NOX emissions from cars fitted with both for comparison but these days I don't have access to an anyliser.

One thing I can say for sure is the car revs more freely with it fitted and doesn't struggle to accelerate when required as it did before, and mpg has increased approx 3mpg which is about 8%. Which is also good for the my wallet and the environment.


Russ
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