795 posts in this topic

EGRs rarely ever actually fail to destruction. They just get dirty and need to be cleaned. Of course these days, the service protocol is to throw them out (though they are perfectly good) and install a new one. Like trading in the car when the ashtray is full. :lol: So much for an environmentally friendly emissions control system. FAIL.:senile:

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Might be worth giving the EGR the benefit of the doubt until it acts up. Mine has been fine for 117,000 km. They replaced it once at 50K km but that was a shot in the dark on another problem, the EGR they removed was pretty much OK.

I still have my Appendix, but many others don't. I wish I didn't! Same goes for EGR after experience with another MB diesel :) If the dealer will replace that abraded EGR hose under warranty, I will ask them to at least inspect the EGR. It's making me think I should change the hose myself.In the end though, I will probably block the egr pipe, but it would be nice to have the electronic fix, at least in the car for emergency use.And Bill - You are right about lifecycle thinking - Save a few $$ on fuel, but throw away egrs and engines?

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EGR has benefits for the engine as well. The recycled exhaust gases lower combustion temperature and help keep EGTs under control.

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EGR has benefits for the engine as well. The recycled exhaust gases lower combustion temperature and help keep EGTs under control.

I've wondered how adding HOT exhaust gas to the intake reduces combustion temp. Wouldn't hotter gases that are starved for O2 require the ECU to add more fuel to maintain the correct mixture, and so actually increase the combustion temperature? :scratch:Somebody help me understand...Bil :sun:

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I've wondered how adding HOT exhaust gas to the intake reduces combustion temp. Wouldn't hotter gases that are starved for O2 require the ECU to add more fuel to maintain the correct mixture, and so actually increase the combustion temperature? :scratch:Somebody help me understand...Bil :sun:

Bill,I am no expert, but as I understand it, on a diesel, the amount of fuel injected is dependent on how hard you push the pedal. As opposed to gas engine where the pedal controls the air.The engine acts like a pump that sucks in air as it rotates. Under many conditions, there is more oxygen in the air than is needed (lean mixture) and this causes fuel to burn hot. By recycling exhaust gas (mostly nitrogen) the % oxygen in the combustion chambers is reduced and the combustion temperature is lowered. This reduces the formation of NOx which is favoured by high temperatures.If anyone can explain this better, please do! Edited by Graham

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OK... I kind of following that, Graham. But if Oxygen is reduced and fuel is the same, doesn't that result in incomplete combustion, which produces smoke - unburnt particulates - and less power produced, requiring you to press harder on the pedal to add more fuel, to suck in more Oxygen, to make more smoke, to... ACKK!!! :brain explodes:

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OK... I kind of following that, Graham. But if Oxygen is reduced and fuel is the same, doesn't that result in incomplete combustion, which produces smoke - unburnt particulates - and less power produced, requiring you to press harder on the pedal to add more fuel, to suck in more Oxygen, to make more smoke, to... ACKK!!! :brain explodes:

My simple minded understanding: Without the EGR, each time the piston goes up and down, it sucks in the same volume of air (mass is different depeding on turbo boost and temperature). Depending on how hard you have pushed the pedal, different amounts of fuel are injected (no throttle plate on a diesel). It is unlikley that you would have insufficient oxygen - the mixtures are always very lean. But you can have too much and that is where the EGR come in. This link may help. If you or others come up with concise answer, please post!

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My simple minded understanding: Without the EGR, each time the piston goes up and down, it sucks in the same volume of air (mass is different depeding on turbo boost and temperature). Depending on how hard you have pushed the pedal, different amounts of fuel are injected (no throttle plate on a diesel). It is unlikley that you would have insufficient oxygen - the mixtures are always very lean. But you can have too much and that is where the EGR come in. This link may help. If you or others come up with concise answer, please post!

Thank you for the link. Reading to do!Bil :sun:

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For the people who have build this circuit, where are you getting the connector to mimic the EGR?

M-B, C0019185V001000000?. Edited by Huronlad

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For the people who have build this circuit, where are you getting the connector to mimic the EGR?

One clever reader (borderlord) used heavy gauge copper wire and inserted the 5 pins directly into the cable going to the EGR Valve connector.This means that the Mercedes cable is not absolutely necessary. Edited by smartdriver

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I recently joined the P0401 club. Figures... my last 400 km or so has been all short city trips and I recently started trying to hit better fuel economy by driving at lower rpm and coasting more. Guess I need to start using fuel additive before trying that again. I've got about 41000 km. Cleared the code but have no reason to believe it won't return. Maybe I'll get lucky and the MB noise-filtering cable is all I'll need.

IF I end up deciding to disable the EGR, I might be inclined to pursue the micro-controller route that was proposed earlier. The main reason would be because my programming skills are better than my circuit-fu skills (and my mechanical skills are almost non-existent!), but also because I like the idea of the preciseness and flexibility of it. And it doesn't hurt that I have a couple Arduino boards lying around looking for a purpose.

I think it might be neat to build an output stage to drive the solenoid with a newly-generated PWM signal so that the micro-controller could operate the valve independently of however the ECU happens to want to operate it. It could then be attached to a known-good valve and precisely calibrated by sweeping the valve through its range of motion and recording its response. A side benefit of having the micro-controller able to connect to the EGR valve would be that for those who want to disable a failed valve, it could automatically test to make sure the valve hasn't failed open and cause the ECU to trigger a code if it has.

It would also open up the possibility of partially disabling EGR. For example, those who have a working valve, but have an opinion on the merits of EGR that is half-way between the opinions of bilgladstone and Mike T, could set a multiplier of 50% so that when the ECU tries to open the valve a certain amount, the micro-controller will open it only 50% of that amount but will report the expected amount openness back to the ECU. The multiplier could be adjustable, or even self-adjusting based on temperature or run-time or other inputs.

From the measurements that I made, it appears that the potentiometer in the EGR valve is not actually a potentiometer (3 terminal device), but a rheostat (variable resistor - 2 terminal device) between pin 2 and +5V (Pin 4).

This implies that the computer may not be measuring the voltage at Pin 2, but might be measuring the current drawn from Pin 2.

What was the verdict of that? I don't know how I'd make a micro-controller draw current from Pin 2 without finding my old electronics textbooks and subsequently bashing my head on them. Edited by Some Guy

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(For some reason, my post above did not trigger the orange "unread posts" thingy on this thread, and the "last action" column in the thread index still shows "Sep 27 2010 - 12:37 PM, Last post by: smartdriver" so I'm making this post as a bump. Please see my post above. Maybe this thread got too long for IPB to handle? :lol:)

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The forum is glitchy today! We will be looking into that.Meanwhile, that is an interesting idea you have.My older smart has been driven gently all its life and the second EGR is good at 115,000 km. Now watch it, I've probbly created a jinx.

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What was the verdict of that? I don't know how I'd make a micro-controller draw current from Pin 2 without finding my old electronics textbooks and subsequently bashing my head on them.

I now think it unlikely that the ECU monitors solenoid current.In the present EGR replacement circuit, a 100 Ohm 2W resistor going to +12V is used as a load to simulate the solenoid.One experiment worth trying would be to use a much larger resistive load (1,000 Ohms?) going to +5V.This would make interfacing your microcontroller circuit much easier.My hands are somewhat tied on all this because my car has been remapped and the EGR valve does not receive a signal to open, although the ECU still requires the 0.8V value indicating that the EGR is closed.

It could then be attached to a known-good valve and precisely calibrated by sweeping the valve through its range of motion and recording its response.

From the information in PropFrog's video it appears that 0.8V represents zero % duty cycle (closed) and 3.0V represents 70% duty cycle (max open).The plot below is from an EGR valve for a Camry.

post-3908-1286376931_thumb.jpg

Edited by smartdriver

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From the information in PropFrog's video it appears that 0.8V represents zero % duty cycle (closed) and 3.0V represents 70% duty cycle (max open).

Yeah, but is voltage what the ECU actually cares about, or does the ECU expect to measure the resistance of a rheostat? That's what my question was (I think you misunderstood, or maybe I misunderstood your piece that I quoted).

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Yeah, but is voltage what the ECU actually cares about, or does the ECU expect to measure the resistance of a rheostat? That's what my question was (I think you misunderstood, or maybe I misunderstood your piece that I quoted).

Sorry, I misunderstood your question.The ECU is looking for a Voltage on Pin 2.As long as the voltage at Pin 2 is between 0.8V and 3.0V the ECU will think that the EGR is properly connected if this voltage tracks the duty cycle.Inside the ECU on Pin 2 is likely a resistor going to ground (1K Ohms?).Inside the EGR valve is a variable resistor (about 5K Ohms) connected between Pin 2 and 5V, the value of which changes with EGR valve position .Varying the resistor in the EGR valve is the same as varying the voltage on Pin 2.The Voltage on Pin 2 will never go below 0.8V because when the EGR valve is closed, the variable resistor inside the EGR valve is at max or about 5K Ohms, which means that Pin 2 has about 0.8V on it.Voltage on Pin 2 (EGR closed) = 1K/(1K + 5K) X 5V = 0.8VAs the EGR valve opens, the variable resistor inside decreases from its maximum 5K Ohms value to a lower value and the Voltage on Pin 2 rises to a max of about 3V at 70% duty cycle.

post-3908-1286548276_thumb.jpg

Edited by smartdriver

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Thanks to MikeT for advising the warranty should cover the EGR Valve for 8years and 130000kms. I will find-out on the 13th at Weber Motors here in Edmonton if they will in fact honor it. The service advisor on phone said that they would. I have had the code P0401 since September 3rd. Scanned it today with scan-gauge for code.

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Just an update. Car is at Weber Motors awaiting to see if Mercedes Canada will cover it under the 130,000km 8year emissions warranty. Fingers crossed

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Sorry for not updating sooner, I thought I had?The car was at Weber Motors for 4 days total while we went back and forth on who would pay the repair. It was determined that I was eligible for only half as a good will gesture. I repeatedly questioned the 130,000km emission warranty. They kept coming back to the 4 year 80,000km warranty being over as the car is 5 years old. I gave up and paid the $440 and picked up my car. I am glad that it is fixed, but to be honest, am tired of Mercedes service for Smart Cars. I was not treated rude or unjust. They were very professionally with me from start to finish. What this has done though is question the long term reliability of my car. With 53000kms on this car and the, in my opinion, high service costs I am starting to question if I would not be better off with a honda or toyota. Hurts me to say that as I love my car. I wish I could wake up someone at Mercedes so they get it. Oh well thanks for reading. :DAlso, thanks to MikeT for suggesting the 130,000km emissions warranty to get it fixed free. Had that not been brought up I am positive I would have paid full price.

Edited by tyrant

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Does anyone make these up, I would be interested in buying one already made up.

Gadget

Is the valve always open or always closed, now? (ie, which way is spring return?)

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This is just for testing. I am going to buy some very large diameter heat shrink tube that will go around the entire thing (and of course remove the foam - it is just on there for the moment so I can zip-tie the board from rattling around).

-Iain

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I was at the dealer today for a new thermostat and we were talking and the parts guy was telling me that they relace a lot of EGR valves. Over $400 just for the part. Later tonight, I cleaned mine up. I don't see how some people are saying that you can clean it up without removing it. I know that I could not have done it in place. BTW the moving shaft on the EGR valve opens two ports internally.

post-6582-1328678077_thumb.jpg

post-6582-1328678157_thumb.jpg

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I cleaned mine also. It was out due to engine blow-up (another thread). Car threw EGR code. Both of the pictures above could have been mine, exactly.Picked unit up from dealer, and a can of carburetor cleaner, a tooth brush, a little paint brush, small screwdrivers as picks and a little swearing and it was clean.An automotive parts cleaner would have been handy, but you improvise when you have to.Dealer jokingly offered me a part-time job cleaning up old parts.Unit works fine, and might be good for another 90,000 Km (hope, hope, hope).BTW... EGR had nothing to do with engine blow-up.

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