Symptoms of malfunctioning EGR - Mercedes-Benz Forum
 
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#1 (permalink) Old 03-19-2008, 03:38 PM
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Symptoms of malfunctioning EGR

Hi Folks, can anyone list the symptoms of a malcuntioning EGR valve.

I know that it will fail emissions. Other than that what kind of things does the car do? Let me know.
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#2 (permalink) Old 03-19-2008, 06:04 PM
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I just went through emissions testing for the 2nd time and failed (see my post). I have done a lot of research and from what I have found, the EGR does have an impact on emissions. From what i have read, the egr valve helps to reduce combustion chamber temps and recycle unburned fuel. Both of these in excess can cause excessive NOx readings which is what you will get if the EGR is not working properly. There are postings on this forum dicussing egr. Also, suggest doing a search on the web under emissions and/or egr. You will find a lot of info. My mech is an emissions guy and he says a blocked or malfunctioning egr will cause or contribute to excessive Nox, which is why i failed the 2nd time. Keep in mind, the repairs i made brought the readings down a lot, and although i failed Nox again, i did pass on hydrocarbons which i failed the first time. There are other contributing factors to the various emissions readings you will get, but I have systematically eliminated and made the needed repairs in those areas (hince the reduction in emissions numbers). My mech says a clean egr system, based on the readings i got should pass the next time. One sympton i know is decreased fuel economy, but search the forum on how to check and the symtoms. I will keep you posted

Last edited by Htown; 03-19-2008 at 06:11 PM. Reason: additional info
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#3 (permalink) Old 03-20-2008, 08:34 AM
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There are my symptoms:

1. Car does not accelerate very well. Takes a long time and a lot of effort pressing on the gas pedal to get it to 60 mph. One of my friends said that there is probably no back pressure as the cat is broken. He says it is the cat.

2. Car shakes, whenever I stop at traffic lights. I went to two different mechanics. Both of them said it was vacuum leak and fixed it. But still car is shaking like anything. Next time if they say vacuum leak, I am going to get my car back. There is something else - either the cat or EGR (last year we put new oxygen sensor, and it is only 6000 miles old)

3. Fuel efficiency has gone down to 9 t0 10 mpg.

So wondering Cat or EGR or something else. Dealer wants $200 to do the diagnostics. Just to tell me what is broken! (If I add another $200, I will probably have a new cat at a road side mechanic)
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#4 (permalink) Old 03-20-2008, 09:45 AM
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There are few indicators of inoperative EGR other than a failed emissions test for NOx. But in hot weather the engine may detonate under hard accell a little. As to the slow acceleration I did not experience that with my clogged up EGR pipe but I did hear detonation from time to time. Once I cleared the crossover pipe the detonation went away as did the vast majority of the NOx. The theory of EGR is interesting in that it's only purpose is to introduce a little bit of inert, already burned gas back into the combustion chanber to lower the combustion temperatures thus lowering oxides of nitrogen (NOx). This fact makes it hard to stay on top of the EGR system as drivers rarely notice that it is not working until they fail an emissions test.
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#5 (permalink) Old 03-20-2008, 09:48 AM
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But one more thing. If the valves diaphragm is torn or the pintle is stuck open, then you'll have either a rough idle all the time (if the vale is stuck open) or a rough vacuum leak type condition when vacuum is applied to the valve.
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#6 (permalink) Old 03-20-2008, 10:03 AM
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One thing i remember prior to replacing the CAT, I did have poor acceleration. Seems like it did not want to reach 60. Turns out the CAT was clogged. As soon as they took it down stuff started falling out. Since the replacement, i have noticed improved performance, but i do believe there are other issues. Seems like I also read somewhere that fuel economy will suffer if the EGR is not functioning. Don't know all the specifics surrounding this gadget, but my mech says the EGR will impact the operation of the car. I will take his word since he has been on point with lots of other stuff so far. Have already ordered the intake gasket. Need to remove the intake to get to the egr pipe to remove and clean. Will check performance after all repairs are made.
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#7 (permalink) Old 03-21-2008, 10:37 AM
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Htown, You don't need to remove the intake to clean out the EGR crossover pipe, it can be done in the car. Removing the intake is quite a job and unless you just want to do it, cleaning the EGR pipe can be done in very little time if done correctly.
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#8 (permalink) Old 03-21-2008, 06:01 PM
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Ramesh,

I think your friend is giving you good advice.

A completely clogged EGR will not exhibit many symptoms.

A clogged catalytic convertor will display all of the symptoms you mention.


Quote:
Originally Posted by Ramesh View Post
There are my symptoms:

1. Car does not accelerate very well. Takes a long time and a lot of effort pressing on the gas pedal to get it to 60 mph. One of my friends said that there is probably no back pressure as the cat is broken. He says it is the cat.

2. Car shakes, whenever I stop at traffic lights. I went to two different mechanics. Both of them said it was vacuum leak and fixed it. But still car is shaking like anything. Next time if they say vacuum leak, I am going to get my car back. There is something else - either the cat or EGR (last year we put new oxygen sensor, and it is only 6000 miles old)

3. Fuel efficiency has gone down to 9 t0 10 mpg.

So wondering Cat or EGR or something else. Dealer wants $200 to do the diagnostics. Just to tell me what is broken! (If I add another $200, I will probably have a new cat at a road side mechanic)

Regards,
Axel

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#9 (permalink) Old 03-21-2008, 06:02 PM
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So what are the procedures for cleaning the EGR pipe on the car?
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#10 (permalink) Old 03-21-2008, 09:15 PM
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An EGR valve can fail in two ways: open or closed. The most common failure mode is failing closed when the vacuum diaphragm gets broken. When this happens, there are usually no adverse symptoms, only the engine can ping if it ran on regular gas. With premium fuel this will not happen. To temporarily fix this issue, the base ignition timing may be slightly retarded

Failing open: This is a more rare failure mode and can happen if enough carbon builds up on the valve stem to hold it open against the action of the compressed spring. The effect of permanently open EGR on engine performance may be very severe, showing similar symptoms as a partially plugged catalytic converter. Power goes down and fuel consumption drastically increases. This is because a lot of exhaust get sucked into the intake, diluting the fuel-air mixture.

You need to remove the valve, clean the stem, test the vacuum diaphragm with a vacuum pump and go from there. Cleaning the EGR feed pipe will not accomplish anything.
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