Choked inlet manifold on ML270

[oigle]

At 100,000km, my inlet manifold, EGR and adjacent hoses are full of viscous black muck. It doesn't appear to have affected the performance to any noticeable degree but would no doubt have done so soon. This is a disgusting result after only a relatively low mileage, most of which has been done under hot running conditions. Ir seems that the fumes from the PCV mix with the carbon particles from the exhaust at the EGR entry and form this glutinous mess. Looks like an awful job to clean it out. Any suggestions as to how?
Secondly, is there anything I can do to reduce or prevent such a buildup occuring again? Should I consider shutting off the EGR? What can I do? I have never seen such a disgusting mess.
Does this occur with petrol engines? I've never seen it before on Japanese engines. Makes me very inclined to go petrol/gas next time.
Any thoughts from experienced people in this area would be appreciated.
Thanks
Ian.

 

[oigle]

No answers guys??

As a follow on, what other areas should I be cleaning out whilst I have this manifold area being done? Are there other problems waiting to raise their heads??

Could I be seeing the first downside of chipping my motor???

 

[meanie]

Common problem on modern diesels. See my thread re Peugeot Hdi's........
http://forums.mercedesclub.org.uk/showthread.php?t=60485
Haven't heard of it creating similar issues with the Mercs though. I've tried blanking the EGR off on 2 Pugs now but the ECU has picked up on it (things not as it should be according to the ECU's outputs I'd guess) & bought the MIL on. Works on the Renault Espace though.

 

[oigle]

Common problem on modern diesels. See my thread re Peugeot Hdi's........
http://forums.mercedesclub.org.uk/showthread.php?t=60485
Haven't heard of it creating similar issues with the Mercs though. I've tried blanking the EGR off on 2 Pugs now but the ECU has picked up on it (things not as it should be according to the ECU's outputs I'd guess) & bought the MIL on. Works on the Renault Espace though.

Thanks for that. The issues shown on the Pug are very much the same as on my ML. I have pulled the manifold off and am getting it acid bathed to remove the gunk. I intend to make the EGR inop and see what happens. Worth a try. As the motor runs on constant boost except at idle or very low revs/throttle backoff, I would guess that the EGR only works then and not on cruise where boost is at least 3 or so pounds. Am I wrong? I intend to remove the front cat too to try to reduce back pressure. Going by the manifold, the cat must be pretty well blocked too. Might see if there is any oil buildup in the bottom of the intercooler too - not that it should make for any noticeable problem. Problem only seems to occur when exhaust gas mixes with the oil.
There was another thread just recently from iphot which finalised with him pulling off his manifold and cleaning it out - that is what started me on the quest. He also had a huge buildup of carbon gunk in there after 250000km. Would have to jam the swirl flaps eventually too. Terrible design really. OK without a turbo where the pcv inlet can be placed strategically in the inlet manifold but to have it pre-turbo is just asking for trouble - of course, there isn't much option as I see it. Pity they can't do away with Egr's and find another way of reducing the NO2's.
As an aside, if I block off the EGR, do you think the fuel/air mix will alter enough to be a problem? As I said, it should only be at idle and backoff and on initial throttle application. Maybe an outside source of filtered air could be supplied through the EGR inlet if necessary. Thoughts??

 

[panason1c]

Back along, as an 'experiment' i tried 'plugging' the egr pipe on my 270CDI ML but as a result the engine would go into limp mode whenever i accelerated hard.

 

[oigle]

Back along, as an 'experiment' i tried 'plugging' the egr pipe on my 270CDI ML but as a result the engine would go into limp mode whenever i accelerated hard.

Wondered about that. As I mentioned above, how do you reckon it would go if I allowed the EGR to work but, rather than allowing it to suck exhaust, let it suck fresh air. Haven't looked at how I would do it, but thought the idea might work. Your thoughts?
When you "plugged" yours, did you block the exhaust entry or did you plug the activating vacuum hose?

 

[meanie]

The pug MIL light came on because the ECU was having to adjust the fuelling outside of what were the recognized parameters to achieve the emission target (at least, that's my theory).

 

[Alex Crow]

hello oigle, nice to see you have a good grasp of the issues here.

the question 'how does the ecu know i have disabled my egr valve?' is answered thus; the ecu watches air mass at idle, and expects it to ba almost halved when the egr valve is open. if, say, the vacuum pipe is disconnected to disable the egr function then the ecu will spot this and trigger fault codes and linited performance.

your suggestion to allow the egr valve to draw in fersh air is a good one, and i look forward to hearing how that goes. perhaps you could duct it from the air filter housing somehow? or just use a seperate filter - the flow rate will not be high - but you must try to avoid any pressure drop from atmospheric obviously.

as for the pcv before the turbo, some supercharged petrols have two systems, with nozzles just before the intake ports which are fitted with a one-way-valve. obviously they also have another breather plumbed in before the compressor which takes over under boost. sadly on the mercedes 111 engine these nozzles and valve are prone to clog, such is the way of complications.

 

[oigle]

hello oigle, nice to see you have a good grasp of the issues here.

the question 'how does the ecu know i have disabled my egr valve?' is answered thus; the ecu watches air mass at idle, and expects it to ba almost halved when the egr valve is open. if, say, the vacuum pipe is disconnected to disable the egr function then the ecu will spot this and trigger fault codes and linited performance.

your suggestion to allow the egr valve to draw in fersh air is a good one, and i look forward to hearing how that goes. perhaps you could duct it from the air filter housing somehow? or just use a seperate filter - the flow rate will not be high - but you must try to avoid any pressure drop from atmospheric obviously.

as for the pcv before the turbo, some supercharged petrols have two systems, with nozzles just before the intake ports which are fitted with a one-way-valve. obviously they also have another breather plumbed in before the compressor which takes over under boost. sadly on the mercedes 111 engine these nozzles and valve are prone to clog, such is the way of complications.

Thanks Alex.
Have been throwing this idea around a bit with my local techie mate. Looked at the setup today and it looked a bit hard to divert fresh air in unless I took off the whole metal block that the EGR attaches to. Not impossible but looked a bit problematical. Wondered it I could achieve the same end result by removing the oil contaminant out of the equation - a dry exhaust shouldn't gum up the works. Was looking at disconnecting the PCV hose from the inlet tract, fitting an old fashioned oil separator to it and venting the remaining gases to a catch tank. I know it is wrong environmentally but, if I use some sort of catch tank for any oil spillage, it would probably work OK. Be an easy one to put back to normal too for a mot.
I would have to seriously clean out all the inlet tubing first to start dry but I reckon it might work. Your thoughts?

 

[Alex Crow]

yup, sounds great and easier than the egr mod.

 

[oigle]

I'll let you know how I finish up. That goo is ****** hard to get out of the manifold. Using a high pressure hot alkali sprayer and it is still stubborn. I'll get there eventually.
Cheers.

 

[oigle]

http://forums.mercedesclub.org.uk/showthread.php?t=65225

Looking at the above thread, admittedly on a different cdi engine, it would appear that removing the actuator of the EGR allowed the engine to run well but allowing the EGR to open caused excessive black smoke. Seems illogical to have extra air entering the manifold causing the mixture to get richer ????? Thought it would work the other way.
Does the same thing apply to my ML270 motor?? I would love to be able to prevent my EGR operating without causing ecu hiccups.
Just looking at all my options before commiting to one.
You seem to be knowledgeable on this front Alex. Any further comments?

 

[Alex Crow]

bear in mind that the egr valve will not allow significantly more or less air into the manifold under zero boost, but if open under any positive boost it will rob the manifold of pressure and consequently air mass, causing an overfuelling situation. note that air mass is measured before the turbo, so any down stream leaks of air mass will not be accounted for in fueling. it is quite common for some egr valves to stick (eg the one on the 613 engine), and we will see black smoke forming at high/full throttle as the egr will be losing air mass into the exhaust system. if your egr valve is functioning correctly i see no reason why allowing it to draw fresh air would give black smoke problems - remember diesels are not throttled anyway, and 99% of the time run with excess air. certainly when egr is open the engine should be in an excess air situation.

 

[dieselman]

You can disable the EGR valve and make a small electrical circuit to fool the MAF, I've done this on my car.

Basically as the EGR transducer is shunted to Gnd by the ECU, that drags the MAF sensor voltage down by about 0.5v so the ECU believes the EGR is working.

You would need to check the connection numbers as this was for a different car but should work ok.

 

[oigle]

Thanks Guys.
Have made the decision to blank off the exhaust from entering the EGR. Have removed the cooler entirely and blanked off exhaust. Have left EGR in place and operational and have mounted a small air filter on to the open end of same.
This should keep the air/fuel mix where it should be, prevent the EGR and manifold from fouling up and consequently sticking and hopefully improve performance by having an unimpeded manifold, a cooler inlet charge and introducing more oxygenated air through the EGR. Hope the theory works out in practice. Will have it going this afternoon so will report on the immediate effects - long term is another issue (hopefully positive).
Thanks for all the advice.

 

[oigle]

bear in mind that the egr valve will not allow significantly more or less air into the manifold under zero boost, but if open under any positive boost it will rob the manifold of pressure and consequently air mass, causing an overfuelling situation. note that air mass is measured before the turbo, so any down stream leaks of air mass will not be accounted for in fueling. it is quite common for some egr valves to stick (eg the one on the 613 engine), and we will see black smoke forming at high/full throttle as the egr will be losing air mass into the exhaust system. if your egr valve is functioning correctly i see no reason why allowing it to draw fresh air would give black smoke problems - remember diesels are not throttled anyway, and 99% of the time run with excess air. certainly when egr is open the engine should be in an excess air situation.

Thanks for that Alex.
I was thinking the valve was sticking closed - not open. Sticking open would surely do what you say. That clarified things.
Am I right in assuming that the EGR only opens on idle or very light throttle and backoff throttle? On cruise, I would think there would be a constant small amount of boost running which would not allow the EGR to operate. What creates the vacuum to operate the EGR? With no butterfly, the manifold would not create any noticeable vacuum.

 

[Alex Crow]

correct that egr does and can only work on zero boost, ie never when cruising. vacuum is created with a dedicated pump mounted on the front of the exhaust cam.

one point i ought to also mention, exhaust gas coming to the egr valve will be at slightly above atmospheric pressure, due to exhaust/turbo back pressure at idle. i would expect this increase above atmospheric to be absolutely minimal, but it could just have a bearing vs MAF values with 'fresh air'.

and DIESELMAN, that is a fantastic solution!! - really impressed. i have pondered this idea before but would not have gone so far as to make it work! glad to hear that it does work though - you should be selling the kits with dedicated plugs and instructions.

 

[oigle]

You can disable the EGR valve and make a small electrical circuit to fool the MAF, I've done this on my car.

Basically as the EGR transducer is shunted to Gnd by the ECU, that drags the MAF sensor voltage down by about 0.5v so the ECU believes the EGR is working.

You would need to check the connection numbers as this was for a different car but should work ok.

Sounds like a simple way of doing it. I have gone the other way but, if it doesn't work out, I'll give that a try.
Thanks
Ian.

 

[dieselman]

and DIESELMAN, that is a fantastic solution!! - really impressed. i have pondered this idea before but would not have gone so far as to make it work! glad to hear that it does work though - you should be selling the kits with dedicated plugs and instructions.

Being fair I didn't design the circuit a poster called Kartech on peachparts did, although I was very aware of what effect the EGR had on the MAF values, having already measured it.
The only bit I hadn't got was whether the feed to the EGR transducer would work because it is modulated.

I'll probably do the VAG car we have as well now as they really filth the manifolds up.

 

[oigle]

correct that egr does and can only work on zero boost, ie never when cruising. vacuum is created with a dedicated pump mounted on the front of the exhaust cam.

one point i ought to also mention, exhaust gas coming to the egr valve will be at slightly above atmospheric pressure, due to exhaust/turbo back pressure at idle. i would expect this increase above atmospheric to be absolutely minimal, but it could just have a bearing vs MAF values with 'fresh air'.

and DIESELMAN, that is a fantastic solution!! - really impressed. i have pondered this idea before but would not have gone so far as to make it work! glad to hear that it does work though - you should be selling the kits with dedicated plugs and instructions.

OK. Job basically done. Quite easy to do once manifold cleaned and replaced. I seem to have a distinct drop in power at this stage - not sure why. Off the mark lag hasn't increased at all (ecu is chipped) but general lowish rev performance seems dull. Once the revs are rocking - over 3000, it seems to be about normal. Thought it might be that the swirl flaps hadn't been hooked up but a visual observation confirmed movement when the throttle is opened. Can't see any bits and pieces not hooked up properly but could have missed something. Wondering if the extra volume of oxygen through the EGR has had an effect on mixture. We always talk about air/fuel mixture but I wonder if it should be called oxygen/fuel mixture. With the quite high volume of oxygen now being introduced through the EGR at idle and low revs, perhaps things have leaned off substantially. If I can't find any other obvious thing put together incorrectly, will try to reduce the input through the EGR - put something in the hole to make it smaller.

Any thoughts as to what else may have been done incorrectly to cause a loss of overall grunt in the lower revs?