my not so well ML270cdi

donithediver

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Hope someone can help here. I have a 2001 ML270cdi ( Auto) that is really draining all my knowledge. Few weeks ago when driving it suddely dropped off power. It seems to be going into a safe mode and only returns to normal after engine is switched off and back on. I first thought it was air mass meter and change it but to no avail. so i replaced with old one. I then noticed the air filter was pretty dirty so changed that. still the same. I had the car looked at by a merc specialist and he spent three hours on it ....siad the air flow meter was only reading -4 and replaced it with the new one i bought earlier. still not going properly. He says now that he suspects the catalyst and says it is giving back pressure. I sometimes here a strange noise almost like a whrrr when revving but it is quite quiet. any advise would be greatful
 

television

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I think that a pipe is split if you have a noise.
What make was the MAF that you fitted.
Welcome to the forum
 
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donithediver

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my ml

Hi,
Thanks for your reply. I bought the maf from ebay and it did not have any details on it however it did list my part number on the advert. I did change it back to the old one when it did not make a differnce. when it went to the merc guy yesterday he diagnosed the maf as problem changed it with the one I had bought and thought that was it. it does it a lot more often since he has changed it. I am after reading a thread tonight leaning towards the auto box. I have Mercedes comming out on Monday to give it a going over to give it a go over....so we will see by then. Many thanks again for your imput
doni
 

Cosworth

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Seems you have a gearbox problem.

When you car goes in limp mode, is it stuck in the same gear. ie 2nd
 
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donithediver

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my ml

not 100% sure. I know I can move it manually but i have never noticed if the gears dont move in auto. will check that out tomorrow.
thanks for your imput
doni
 

television

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Most Ebay MAF's only last a few weeks
 

LOTTY

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I have a similar sort of problem.....when i drive along after about 10min the car goes into limp mode. There are no warning lights on, i have noticed there's no kick down. However, if i turn it off then restart it seems better for a while. Its been plugged in and no faults come up. So if you get to the bottom of your fault let me know.
 

Alex Crow

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hello lotty, there WILL be fault codes logged in either the cdi or etc modules, possibly both.
 

panason1c

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Blocked primary cat is a known problem on ML's, disconnect the clamp on the exhaust downpipe where it connects to the turbo and see if the problem still exists.

As television states, ebay mafs are not always reliable, a genuine maf from MB is only circa £60.
 
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donithediver

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This site is so helpful. Was out in it yesterday and the gears are going up and down as they should. I did have a look at the exhaust system and there looks to me like a cat under the air intake in the area of the turbo..... however there looks like a smaller cat further along the exhaust before the silencer.... would this be correct. I suspect it is going to be really noisy disconnecting from the back of the turbo but at least I would now if it is blocked or not. Do these clamps that are on the exhaust go back on easy or should I buy new ones before I start removing the old ones? Anyway thanks again for for all your help you have gave me some good ideas
doni
 

Alex Crow

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yes, 2x cats. clamps come off and go on very easily, yours should be fine to re-use. obviously you cannot drive for long like this, and it will only be diagnostic if the fault is constant before you remove the clamp. i should point out that there are many things that can cause a lack of power, the common blocked cat scenario is only one. where are we with fault codes? and if the fault is constant you really want to have the live data (boost pressure etc) checked on a roadtest - just hunt out a local specialist.

where are you located??
 

panason1c

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"it is going to be really noisy disconnecting from the back of the turbo but at least I would now if it is blocked or not".


Yes, it will be noisy but it is the easiest/quickest way to diagnose a blocked cat............if the cat is blocked it is likely to be only be the primary cat that is affected as it acts almost like a filter protecting the 2nd cat situated nearer to the back of the car.

If it is blocked i would just 'de-cat' it.....(hit out the cat innards) .........cats are not reqiured on diesels for the mot test and you might even find a slight performance increase.
 

Alex Crow

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cat removal seconded, if it needs it, easily done and cheap!! will make a different noise though but not too intrusive. beware the second cat getting blocked when the first rattles about creating debris. if needed just backflush the second cat, usually works great and nothing to loose.
 
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donithediver

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my not so well ml270 latest update....

Hi all,

The latest in the cure to my ML problems is... Today I removed the air filter box. I then removed the primary cat. I could not determin any blockage but I did think about decating it but as Mercedes are coming out tomorrow thought I would give them a chance to pinpoint the defect first. Anyway the job went alright so I continued on to the secodary cat. This is when it became interesting. There is a loud rattle in the secondary cat that sound as if the whole insides are moving around. but not as easy to remove due to the shape of the pipework at either end. So I have replaced all the bits and after Mercedes have been to visit tomorrow I will remove it again cut it open and reweld it shut or just buy a new one. Anyway It is going to need seen to regardless of tomorrows visit. One more thing I need to ask... what is the adjuster on the air filter box for... you know the twist knob that reads 75 or 100 %. I suspect it is a winter summer thing but not sure.
thanks again
doni
 

panason1c

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"what is the adjuster on the air filter box for"

That is a guage to monitor the restriction (blockage) of the air filter......ie..100% is a totally blocked filter.....the knob is to reset the guage after fitting a new filter.
 

Alex Crow

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^^^and if it shows any red, the filter will be filthy! change if any reading is shown whatsoever.
 
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donithediver

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Well I am quite impressed. Mercedes came out today and this is the offical defect list.
No 3 glow plug electrical fault. Causing Light to stay on longer than norm
Cat has broken up causing charge pressure to be to low
egr rate to low
hfm signal to low
Still to speak to mercedes to find out what egr and hfm are. But cat issue will definatley need sorted
 

Alex Crow

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hfm signal = maf sensor signal = mass air flow sensor signal. egr = eghaust gas recirculation, could be many causes, but egr rate is checked using hfm signal so go for that first, only about £65 for new MB maf sensor.
 

panason1c

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"Cat has broken up causing charge pressure to be to low"

egr rate too low and hfm signal too low could be symptoms of the cat blockage which is causing low turbo boost and should correct themselves when the cat fault is sorted.
 


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